JPH1028023A - Variable gain amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To widen the variable gain width of an amplifier in the range of the low level of limited input signals by limiting the gain of the amplifier by limiting the maximum value of a control current by the second constant current of a second constant current source. SOLUTION: A first constant current 11 from a first constant current source 15 is branched into the output current of a function generator and the input of a first current mirror circuit 14 and supplied, the second constant current 12 is branched into the output of the first current mirror circuit 14 and the input of a second current mirror circuit 16 and supplied from the second constant current source 17 and the control current Icont of the amplifier 12 is taken out by the output of the second current mirror circuit 16. In this case, when the output of the first current mirror circuit 14 becomes 'O', the control current Icont becomes a value corresponding to the second constant current and the control current Icont becomes the maximum value. Thus, the maximum value of the control current Icont of the amplifier 12, thus the maximum value of the gain, is accurately set by the second constant current 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable gain amplifying apparatus, for example, an automatic gain control (abbreviated as A) of a radio receiver.
The present invention relates to a variable gain amplifying device which can be suitably implemented in a GC) circuit.

[0002]

2. Description of the Related Art A typical prior art is shown in FIG. The amplifier 1 has a pair of transistors 2 and 3 and resistors 4 and 5
The input signal Vin is input between the bases of these transistors 2 and 3, and the output signal Vout is derived from between the collectors. The gain is determined by transistors 2, 3
Corresponding to the control current Icont taken out via the line 6 from the commonly connected emitters.

In order to control the gain of the amplifier 1, a transistor 7 and a resistor 8 are provided, and an input control signal Vcont is given to a base of the transistor 7. The voltage of the input control signal Vcont, that is, the control current Icont flowing through the line 6 changes linearly. Amplifier 1
The transistors 2 and 3 constitute a differential amplifier.

[0004]

In the prior art shown in FIG. 27, if the variable width of the gain of the amplifier 1 is to be widened, the voltage of the input control signal Vcont must be changed within a range corresponding thereto. For example, assuming that the variable width of the gain is 60 dB, the voltage of the input control signal Vcont (in the following description, the reference numeral Vcont may represent the voltage) requires a 1000-fold voltage change. Assuming that the minimum value of the voltage of the input control signal Vcont is 10 mV, the maximum value is 10 V. Therefore, there is a problem that the power supply voltage must be increased in order to widen the variable width of the gain.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a variable gain amplifying device capable of widening the variable gain range of an amplifier in a small range of the level of an input control signal.

[0006]

According to the present invention, a control current Ic is provided.
an amplifier having a gain corresponding to ont, a function generator whose output current increases in accordance with a predetermined characteristic according to an increase in the level of the input control signal Vcont, a first current mirror circuit, and a predetermined first constant current Is supplied to the output of the function generator and the input of the first current mirror circuit, and a control current Icon of the amplifier.
a second current mirror circuit that derives t as an output,
A second predetermined value corresponding to the maximum value of the control current Icont
And a second constant current source that branches and supplies the constant current to the output of the first current mirror circuit and the input of the second current mirror circuit. The present invention according to claim 1 corresponds to an embodiment of the present invention shown in FIGS. 1 to 3 described later, and according to a predetermined characteristic of the function generator 13, for example, the voltage of the input control signal Vcont in a small change range. Depending on the level, the output current of the function generator is greatly changed, whereby the control current Icont of the amplifier 12 is changed in a large change range, so that the variable range of the gain of the amplifier can be widened. Therefore, the power supply voltage for input control signal Vcont may be low. According to the first aspect of the present invention, the maximum value of the gain of the amplifier can be accurately set. The first constant current I1 from the first constant current source 15 is branched and supplied to the output current of the function generator and the input of the first current mirror circuit 14, and
The second constant current I2 from the constant current source 17 is branched and supplied to the output of the first current mirror circuit 14 and the input of the second current mirror circuit 16, and the amplifier is controlled by the output of the second current mirror circuit. The current Icont is taken out. When the output current of the first current mirror circuit becomes zero, the control current Icont becomes a value corresponding to the second constant current,
The control current Icont has a maximum value. The amplifier has a gain corresponding to the control current Icont. Therefore, the control current I of the amplifier is controlled by the second constant current of the second constant current source.
The maximum value of cont, that is, the maximum value of gain can be set with high accuracy. Thus, according to the present invention, the gain of the amplifier is not limited by the voltage but is controlled by the control current Ico.
Since the maximum value of nt is limited by the second constant current of the second constant current source, the maximum value of the gain of the amplifier can be accurately set as described above. On the other hand, in the prior art described with reference to FIG. 27 described above, the amplifier 1 is controlled by the voltage between the terminals 9 and 10 of the DC power supply.
Is limited, and the fluctuation of the power supply voltage changes the gain. The present invention solves this problem.

Further, according to the present invention, a predetermined third constant current corresponding to the minimum value of the control current Icont is set to the control current Ic.
A third constant current source that is provided as a part of ont is provided. The present invention according to claim 2 corresponds to an embodiment shown in FIGS. 4 and 5 described later, and corresponds to a control current Icont taken out of the amplifier.
Is set by the third constant current source 59. Thus, according to the first and second aspects of the present invention, it is possible to prevent the maximum value and the minimum value of the gain of the amplifier from varying for each product.

According to the present invention, the mirror ratio of the first current mirror circuit is determined so that the output current I4 flowing when the input current of the first current mirror circuit is maximum is equal to or more than the second constant current I2. And According to the third aspect of the present invention, in the configuration of the second aspect, the output current Iout of the function generator becomes a minimum value, for example, zero, so that the input current I3 of the first current mirror circuit 14 becomes the first constant current source 15. In the state where the value becomes equal to the first constant current I1 and reaches the maximum value, the second constant current source 17
The constant current I2 is equal to the input current I of the second current mirror circuit 16.
5, the entirety of the second constant current I2 flows as the output current I4 of the first current mirror circuit 14. As a result, the control current Icont of the amplifier is not branched and extracted by the output of the second current mirror circuit 16. Thus, the minimum value of the control current Icont can be accurately set by the third constant current I6 from the third constant current source 59.

The present invention also provides an amplifier having a gain corresponding to the control current Icont, a function generator whose output current increases in accordance with a predetermined logarithmic function characteristic in response to an increase in the level of the input control signal Vcont, Icon
The predetermined constant current corresponding to the minimum value of t is controlled by the control current I
The variable gain amplifying device is provided with a constant current source which is taken out as a part of cont. The invention according to claim 4 corresponds to the embodiment of FIG. 6, and the control current Icont of the amplifier can be changed by a function generator having a logarithmic function characteristic.
The minimum value of cont can be accurately set by the constant current source 59. As a result, the minimum gain of the amplifier can be fixed, and the minimum gain of the variable gain amplifier of the present invention does not vary for each product sample. That is, even in a range where the function generator based on the input control signal Vcont does not operate, the control current Icont of the amplifier is drawn by the constant current source 59, so that the minimum gain is fixed.

According to the present invention, (a) a pair of transistors whose emitters are connected in common, an input signal to be amplified is applied between the bases of these transistors, and the amplified signal is amplified from the collector of the transistor. An amplifier whose output signal is derived and has a gain corresponding to the control current Icont drawn from said commonly connected emitters;
(B) a logarithmic conversion circuit comprising a first resistor R1 and a second resistor R2, one end of the first resistor R1 and a second resistor R2;
A second resistor R2 to which an input control signal Vcont is applied between the first resistor R1 and the other end of the first resistor R1, and an emitter connected to the other end of the second resistor R2. A first transistor Q1 to be connected, a base to which the base of the first transistor Q1 is connected, a collector connected to the commonly connected emitter of the amplifier,
A second emitter connected to the one end of the second resistor R2;
And a logarithmic conversion circuit having a transistor Q2. The invention of claim 5 corresponds to the embodiment of the invention shown in FIG. 7 and FIG. 8, and controls the control current Icont of the amplifier by:
The output can be controlled by the output of a logarithmic conversion circuit, and the output current of the logarithmic conversion circuit, that is, the control current Icont of the amplifier, changes in a logarithmic manner in response to the input control signal Vcont, thereby increasing the variable range of the gain. be able to.

According to the present invention, (a) a pair of transistors having emitters connected in common, an input signal to be amplified is provided between the bases of these transistors, and amplified from the collector of the transistor. An amplifier whose output signal is derived and has a gain corresponding to the control current Icont drawn from said commonly connected emitters;
(B) a current mirror circuit for extracting the control current Icont in accordance with an input current; and (c) a logarithmic conversion circuit, which is a first resistor R1, a second resistor R2, and one end of the first resistor R1. A second resistor R2 to which an input control signal Vcont is applied between the second resistor R2 and one end of the second resistor R2, a collector and a base are commonly connected to the other end of the first resistor R1, and an emitter is connected to the second resistor R2. The first connected to the other end of R2
A transistor Q1 has a base to which the base of the first transistor Q1 is connected, supplies the input current from a collector to a current mirror circuit, and has an emitter connected to a second resistor R2.
And a logarithmic conversion circuit having a second transistor Q2 connected to the one end of the variable gain amplifier. The present invention of claim 6 corresponds to the embodiment of FIGS. 9 and 10, and corresponds to the case where the logic of the input control signal Vcont in the configuration of claim 5 corresponding to FIGS. 7 and 8 is reversed. . In the configuration of the present invention, the input control signal Vcont
26 can be non-inverted, and the output of the detection circuit shown in FIG. 26 can be received with a high input impedance. Also, due to the configuration of the loop, when the voltage of the input control signal Vcont rises,
The characteristic is that the gain of the amplifier decreases.

According to the present invention, (a) a pair of transistors whose emitters are connected in common, an input signal to be amplified is given between the bases of these transistors, and amplified from the collector of the transistor. An amplifier whose output signal is derived and has a gain corresponding to the control current Icont drawn from said commonly connected emitters;
(B) a current mirror circuit for supplying an output current corresponding to the input control signal Vcont; and (c) a logarithmic conversion circuit, wherein a resistor, a collector and a base are commonly connected, and an output from the current mirror circuit is provided. A first transistor having a current supplied thereto, an emitter connected to one end of the resistor, a base connected to the base of the first transistor, a collector connected to the commonly connected emitter of the amplifier, And a logarithmic conversion circuit having a second transistor connected to the other end of the resistor. The present invention according to claim 7 corresponds to an embodiment of FIG. 11 described later, which has a configuration in which the connection mode of the current mirror circuit and the logarithmic conversion circuit in the above-described claim 6 is reversed.

The present invention also provides (a) a pair of transistors whose emitters are commonly connected, an input signal to be amplified is provided between the bases of these transistors, and the input signal is amplified from the collector of the transistor. An amplifier whose output signal is derived and has a gain corresponding to the control current Icont drawn from said commonly connected emitters;
(B) a current mirror circuit for extracting the control current Icont in accordance with an input current; (c) a control transistor; and (d) an operational amplifier, one input terminal to which an input control signal is supplied; An operational amplifier having the other input terminal connected to the emitter of the control transistor and an output terminal connected to the base of the control transistor; and (e) connecting between the other input terminal of the operational amplifier and one terminal of the power supply. (F) a logarithmic conversion circuit, a resistor having one end connected to the other terminal of the power supply, and a collector and a base commonly connected to the collector of the control transistor. , A first transistor having an emitter connected to the other end of the resistor, and a base connected to the base of the first transistor. Supplying a power current, a variable gain amplifier which comprises a logarithmic converter circuit having a second transistor whose emitter is connected to the other terminal of the power supply. The invention according to claim 8 corresponds to the embodiment of FIG. 12, and the base-emitter voltage of the first transistor Q1a provided in the logarithmic conversion circuit according to the invention corresponding to FIGS. 9 and 10 of claim 6. The variation in the gain of the amplifier due to the variation in V _BE is reduced. That is, in the configuration of the fifth aspect, the logarithmic conversion circuit has a low input impedance, and therefore cannot use an output voltage having a poor load characteristic as it is as the voltage of the input control signal Vcont. The variation in the voltage V _BE of the first transistor in the logarithmic conversion circuit is directly related to the control current Ic.
There is a problem that the variation in ont is caused, and therefore, the absolute value of the gain varies. In order to solve this problem, the invention according to claim 8 includes a control transistor 66, an operational amplifier 67, and a control resistor R3, and increases the input impedance of one input terminal to which the input control signal Vcont of the operational amplifier is applied. Thus, the variation in the gain of the product sample is suppressed.

According to the present invention, (a) a pair of transistors whose emitters are connected in common, an input signal to be amplified is applied between the bases of these transistors, and amplified from the collector of the transistor. An amplifier whose output signal is derived and has a gain corresponding to the control current Icont drawn from said commonly connected emitters;
(B) a current mirror circuit for supplying an output current corresponding to the input current; and (c) a logarithmic conversion circuit, wherein an emitter resistor, a collector and a base are commonly connected, and an output current from the current mirror circuit is provided. A first transistor having an emitter connected to one end of the emitter resistor, a base connected to the base of the first transistor, a collector connected to the commonly connected emitter of the amplifier, A logarithmic conversion circuit having a second transistor connected to the other end of the emitter resistor;
(D) a control transistor for flowing the input current of the current mirror circuit, and (e) an operational amplifier, one input terminal to which an input control signal Vcont is supplied, and the other connected to the emitter of the control transistor. (F) including an operational amplifier having an input terminal and an output terminal connected to the base of the control transistor, and (f) a control resistor R6 connected between the other input terminal of the operational amplifier and a power supply. This is a variable gain amplifying device. The ninth aspect of the present invention corresponds to the embodiment of FIG. 13 and changes the input format in the configuration of the seventh aspect of the present invention corresponding to FIG. Variation in gain of the amplifier due to variation in _BE can be reduced.

According to the present invention, (a) a pair of transistors whose emitters are connected in common, an input signal to be amplified is supplied between the bases of these transistors, and the amplified signal is amplified from the collector of the transistor. An amplifier whose output signal is derived and has a gain corresponding to the control current Icont drawn from said commonly connected emitters;
(B) a control resistor R4 having one end connected to one terminal of the power supply; (c) a logarithmic conversion circuit, an emitter resistor having one end connected to the other terminal of the power supply; a collector and a base. Are connected in common to receive an output current from the current mirror circuit, and have a first transistor whose emitter is connected to the other end of the emitter resistor, a base to which the base of the first transistor is connected, and a collector Is connected to the commonly connected emitter of the amplifier, and a logarithmic conversion circuit having a second transistor having the emitter connected to the other end of the emitter resistor; and (d) connected to the other end of the control resistor R4. A control transistor having an emitter connected to the collector of the first transistor of the logarithmic conversion circuit; and (e) an operational amplifier provided with an input control signal. A variable gain amplifying device having an operational amplifier having one input terminal connected to the control transistor, another input terminal connected to the emitter of the control transistor, and an output terminal connected to the base of the control transistor. It is. Claim 10 corresponds to the embodiment of FIG. 14 and, like the above-mentioned inventions, changes the input format of the input control signal Vcont and provides the first transistor Q provided in the logarithmic conversion circuit.
The variation in the gain of the amplifier due to the variation in the base-emitter voltage V _BE can be reduced.

According to the present invention, (a) a pair of transistors whose emitters are connected in common, an input signal to be amplified is applied between the bases of these transistors, and amplified from the collector of the transistor. An amplifier from which an output signal is derived and having a gain corresponding to a control current Icont extracted from the commonly connected emitter; (b) a current mirror circuit for extracting the control current Icont corresponding to an input current; and (c) a power supply. Having a collector connected to one terminal of the first
A control transistor, (d) a first operational amplifier, one input terminal to which an input control signal is supplied, another input terminal connected to an emitter of the first control transistor, and a first control transistor. A first operational amplifier having an output terminal connected to the base of (e), and (e) a plurality of gain switching circuits, each of the gain switching circuits being (e1) one end connected to the emitter of the first control transistor. (E2) a second control transistor having an emitter connected to the other end of the control resistor, and a collector for providing an input current to the current mirror circuit; and (e3) a reference voltage source. (E4) one input terminal to which the voltage of the reference voltage source is applied; the other input terminal connected to the emitter of the second control transistor; (E5) the voltage of the reference voltage source for each gain switching circuit includes a mutually different gain switching circuit. It is a variable amplification device. Claim 11 corresponds to the embodiment of FIGS. 15 to 18,
According to each of the gain switching circuits A1 to Au, the current value input to the current mirror circuit 16 is converted into a voltage / current (a current value corresponding to the input control signal Vcont flowing through the first control transistor) which changes in a plurality of stages. V / I) The variable width of the gain of the amplifier 12 is widened using the conversion characteristics. Since each gain switching circuit uses a second operational amplifier, V / I
The current value of the conversion characteristic can be set accurately, and the gain of the amplifier has high accuracy.

According to the present invention, (a) a pair of transistors whose emitters are connected in common, an input signal to be amplified is applied between the bases of these transistors, and the signal is amplified from the collector of the transistor. An amplifier from which an output signal is derived and which has a gain corresponding to the control current Icont drawn from the commonly connected emitter; and (b) the control current Icont corresponding to a first input current.
(C) a second current mirror circuit that outputs a first input current of the first current mirror circuit in response to a second input current; and (d) a second current mirror circuit that outputs a second current mirror circuit. (E) a first operational amplifier having a collector through which an input current flows; and (e) a first operational amplifier, one input terminal to which an input control signal is applied, and the other connected to an emitter of the first control transistor. (F) a plurality of gain switching circuits, wherein each of the gain switching circuits comprises (f1) a first operational amplifier. A control resistor having one end connected to the emitter of the control transistor, an emitter connected to the other end of the control resistor, and an input current to the second current mirror circuit. A second control transistor having a collector, (f3) a reference voltage source, and (f4)
One input terminal to which the voltage of the reference voltage source is applied;
(F5) a second operational amplifier having another input terminal connected to the emitter of the control transistor and an output terminal connected to the base of the second control transistor;
The voltage of the reference voltage source for each gain switching circuit includes a gain switching circuit different from each other, and (g) a gain operating resistor for branching and flowing a current from the emitter of the first control transistor. Variable gain amplifying device. The twelfth aspect of the present invention corresponds to the embodiment of FIGS. 19 to 21, and makes the voltage of the input control signal Vcont wider than that of the above-described embodiment shown in FIGS. Can be taken. In other words, according to the characteristics of FIGS. 16 and 18 corresponding to the eleventh aspect of the invention, when the reference voltage is less than the minimum reference voltage, the control current Icont of the amplifier becomes zero, whereby the gain of the amplifier becomes zero.
Therefore, in the twelfth aspect of the present invention, the first and second current mirror circuits 16, 10 are used by using the gain operation resistor R7.
0, and thus the control current Icont,
Even if cont is a small value, it is possible to take out and perform input control. Thus, the change range of the input control signal Vcont in which the gain of the amplifier can be controlled can be widened.

According to the present invention, (a) a pair of transistors whose emitters are connected in common, an input signal to be amplified is applied between the bases of these transistors, and the amplified signal is amplified from the collector of the transistor. An amplifier having an output signal derived and having a gain corresponding to the control current Icont extracted from the commonly connected emitter; (b) a current mirror circuit extracting the control current Icont corresponding to the input current; and (c) a current mirror circuit. A first control transistor having a collector for flowing an input current to the mirror circuit; and (d) an operational amplifier, one input terminal to which an input control signal is supplied, and the other connected to an emitter of the first control transistor. A first operational amplifier having an input terminal and an output terminal connected to the base of the first control transistor; (E) a plurality of gain switching circuits, each gain switching circuit comprising: (e1) a control resistor having one end connected to the emitter of the first control transistor; and (e2) the other end of the control resistor. A second control transistor having an emitter connected to the section, a collector for supplying an input current to the current mirror circuit, (e3) a reference voltage source, and (e4) one input terminal to which a voltage of the reference voltage source is supplied. And a second operational amplifier having another input terminal connected to the emitter of the second control transistor and an output terminal connected to the base of the second control transistor, and (e5) each gain switching A gain characterized in that the voltage of the reference voltage source for each circuit includes: a gain switching circuit different from each other; and (f) a gain operating resistor that branches and supplies a current to the emitter of the first control transistor. It is a variable amplification device. The present invention of claim 13 corresponds to the embodiment of FIGS. 22 and 23, and has a configuration in which the logic of the input control signal Vcont in the configuration corresponding to the embodiment of FIGS. And changes so that the gain of the amplifier decreases as the voltage of the input control signal Vcont increases.

According to the present invention, (a) a pair of transistors whose emitters are connected in common, an input signal to be amplified is given between the bases of these transistors, and the amplified signal is amplified from the collector of the transistor. An amplifier from which an output signal is derived and which has a gain corresponding to the control current Icont drawn from the commonly connected emitter; and (b) the control current Icont corresponding to a first input current.
(C) a second current mirror circuit that outputs a first input current of the first current mirror circuit in response to a second input current; (d) a first control transistor; (E) a first operational amplifier, one input terminal to which an input control signal is applied, the other input terminal connected to the emitter of the first control transistor, and the base connected to the first control transistor. (F) a plurality of gain switching circuits, wherein each gain switching circuit has one end connected to the emitter of the (f1) first control transistor. A second control transistor having a resistor, (f2) an emitter connected to the other end of the control resistor, and a collector for providing an input current to the current mirror circuit; and (f3) a reference voltage source. (F4) one input terminal supplied with the voltage of the reference voltage source, the other input terminal connected to the emitter of the second control transistor, and the output terminal connected to the base of the second control transistor. And (f5) a voltage of the reference voltage source for each gain switching circuit includes a gain switching circuit different from each other. The invention according to claim 14 corresponds to the embodiment of FIGS. 24 and 25, in which a saturation voltage between the collector and the emitter of the first control transistor 123, for example, an input control signal Vcont having a value of 0.2 V or more is used. The gain of the amplifier 12 can be controlled. 22 and 23 corresponding to claim 13 described above, the saturation voltage between the collector and the emitter of the first control transistor 107, for example, 0.2 V, and the first control transistor 107 Of the input control signal Vcont having a value of not less than the sum (= 0.2 + 0.7 V) of the base-emitter voltage V _BE of the transistor 32 of the current mirror circuit 16 to which the current of Can change the gain of the amplifier. On the other hand, according to the fourteenth aspect of the present invention, the input control signal V
The gain can be changed to a lower value to the left of FIG. 25 than the voltage of cont. Therefore, the range of the voltage of input control signal Vcont for changing the gain can be widened.

[0020]

FIG. 1 is an electric circuit diagram showing a configuration of an embodiment of the present invention. This variable gain amplifier basically includes an amplifier 12, a logarithmic conversion circuit 13, which is a function generator, a first current mirror circuit 14, a first constant current source 15, and a second current mirror circuit. Circuit 16
And a second constant current source 17. The amplifier 12 has a pair of transistors Q01 and Q02 whose emitters are connected to the connection terminal 18 and the line 19, and an input signal Vin to be amplified is given between the bases of the transistors Q01 and Q02. Transistors Q01, Q02
Are connected to a line R which is one terminal Vcc of the DC power supply.
The other terminal 23 of this DC power supply is indicated by line 21. An amplified output signal Vout is derived between the collectors of the transistors Q01 and Q02. The transistors Q01 and Q02 have the same characteristics and constitute a differential amplifier, and the resistors R01 and R02 have the same resistance value. The gain G of this amplifier 12 corresponds to the control current Icont drawn via line 19.

[0021]

(Equation 1)

Here, re is the transistors Q01, Q0
2 indicates the emitter resistance, k indicates Boltzmann's constant, T indicates temperature, and q indicates electric charge.

The gain G of the amplifier 12 in Equation 1 is equal to the control current I
It turns out that it is directly proportional to cont.

The logarithmic conversion circuit 13 receives the input control signal Vco
It has input terminals 22 and 23 to which nt is given. One end of the first resistor R1 is connected to the input terminal 22 and the second resistor R1
One end of 2 is connected to the input terminal 23. The collector and the base of the first transistor Q1 are commonly used as the first resistor R1.
And the emitter is connected to the other end of the second resistor R2. The second transistor Q2 has a base to which the base of the first transistor Q1 is connected, a collector connected to the connection point 24, and an emitter connected to the one end of the second resistor R2, and thus to the input terminal 23. .

The current mirror ratio γ in the logarithmic conversion circuit 13,

[0026]

(Equation 2)

Is determined as follows. Iin is the input current of the input terminal 22, and Iout is the output current Iout flowing through the collector of the second transistor Q2. Equation 4 holds for the potentials of the transistors Q1 and Q2.
Ln is a natural logarithm.

[0028]

(Equation 3)

Here, Is indicates a current flowing in the unit emitter area of the transistors Q1 and Q2, and n and m are coefficients of the current Is. Equation 5 holds for the current Iin.

[0030]

(Equation 4)

The base-emitter voltage V _BE of the transistor Q 1 is VT · Ln
Iin / n · Is, which is actually about 0.7V.
Equation 6 is established by substituting Equation 5 into Equation 4.

[0032]

(Equation 5)

Α and β are constants. Therefore, it is understood that the output current Iout in the logarithmic conversion circuit 13 increases in accordance with the characteristic of a predetermined logarithmic function as the voltage level Vcont of the input control signal Vcont increases. The reference sign Vcont is used to represent the input control signal and its voltage.

The first and second constant current sources 15 and 17 are realized by transistors 25 and 26 whose bases are commonly connected, and their bases are connected to the base of a transistor 27. The base and the collector of the transistor 27 are commonly connected, and the base of the transistor 27 is connected to the constant current source 28. A first constant current I1 is supplied from the collector of the transistor 25, and a second constant current I2 is supplied from the collector of the transistor 26.

The first current mirror circuit 14 has two transistors 27 and 28. The base of transistor 27 is connected to a collector, which is connected to line 29
To the connection point 24 via The base of transistor 27 is connected to the base of transistor 28. The collector of the transistor 28 is connected to a connection point 31, and the second constant current I 2 from the transistor 26 is connected to the connection point 31.
Is supplied. Transistors 27 and 28 have the same characteristics, so that current I3 flowing in line 29 may be equal to current I4 flowing in the collector of transistor 28, but may be different.

[0036] The second current mirror circuit 16 also has a transistor 32 whose base and collector are commonly connected, and another transistor 33, and the collector of the transistor 32 is connected to a connection point 31 via a line 34. The collector of the transistor 33 is connected to the line 19, and the control current Icont is taken out. The current I5 flowing in the line 34 may be equal to the control current Icont, but may be different.

For example, when the configuration is such that I3 = I4 and I5 = Icont, from Expressions 7 and 8, Expression 9 is satisfied. Icont = I2-I1 + Iout (9) Input control given to logarithmic conversion circuit 13 Signal Vcont
Accordingly, when the output current Iout becomes equal to the first constant current I1, I3 = I4 = 0, and the current I5,
Therefore, the control current Icont has a maximum value equal to the second current I2.

FIG. 2 is a graph showing the relationship between the voltage of the input control signal Vcont and the control current Icont. The control current Icont changes according to the characteristics of the line 35,
Accordingly, the gain G of the amplifier 12 changes. As the input control signal Vcont increases, the currents I3 and I4 decrease, as shown by line 36. The second constant current I2 by the transistor 26 can be changed by connecting an emitter resistor to the transistor 26 or changing its emitter area, which is the same for the transistor 25.

In the embodiment of the present invention shown in FIGS. 1 and 2, the maximum gain of the amplifier 12 is fixed by the second constant current I2 of the transistor 26 constituting the constant current source 17, whereby the product sample is obtained. By preventing the maximum gain from varying every time and by limiting the maximum value of the control current Icont, the maximum value of the gain can be set with high accuracy, and the DC power supply voltage between the lines 20 and 21 can be reduced. Thus, it is possible to prevent the gain of the amplifier 12 from varying. Therefore, in a configuration in which the change range of the input control signal Vcont is small using the logarithmic conversion circuit 13 and the gain G is changed widely, it is possible to prevent the gain G from greatly varying due to the variation of the DC power supply voltage.

In the prior art shown in FIG. 27, the control current Icont is controlled by the input control signal Vcont.
Varies as shown by line 38, but the present invention allows the control current Icont, and thus the maximum value of the gain of amplifier 12, to be fixed at a desired value.

FIG. 3 is a more specific electric circuit diagram of another embodiment of the present invention. 1 and 2 are denoted by the same reference numerals. The input signal Vin to be amplified is applied to the base of the transistor Q01 via the capacitor 39. The bias power supply B1 is connected to the base of the transistor Q02. Another bias power supply B2 is connected to the collector of the transistor Q02 via a resistor R03. The collector of the transistor Q02 is derived as the output signal Vout. Further, transistors 40 to 42 are connected in connection with transistors Q01 and Q02. In addition to the embodiment shown in FIG. 1, in the embodiment shown in FIG.
Are connected, and transistors 56 and 57 are provided.

FIG. 4 is an electric circuit diagram of still another embodiment of the present invention. This embodiment is similar to the embodiment shown in FIGS. 1 and 2 described above, and corresponding parts are denoted by the same reference numerals. It should be noted that a third constant current source 59 is provided in this embodiment. The third constant current source 59 has a third constant current source 59 corresponding to the minimum value of the control current Icont.
Is taken out as a part of the control current Icont.

When the control current Icont of the amplifier 12 is
In order to ensure that the current ratio is set by the third constant current I6 of the constant current source 59, the mirror ratio of the first current mirror circuit 14 is set such that when the input current I3 of the first current mirror circuit 14 is at a maximum, the transistor The output current I4 flowing through the second constant current 28 is determined to be equal to or more than the second constant current I2 (I4 ≧ I2). Therefore, by the input of the input control signal Vcont, all of the second constant current I2 flowing from the transistor 26 of the second constant current source 17 flows as the current I4 to the transistor 28 of the first current mirror circuit 14, thereby setting I5 to zero. That is, the current I7 flowing through the transistor 33 of the second current mirror circuit 16 can be made zero. As a result, the control current I of the amplifier circuit 12
cont can be fixed by the third constant current I6 of the third constant current source 59.

In another embodiment of the present invention, the mirror ratio of the first current mirror circuit 14 is determined by the output current I 3 flowing when the input current I 3 of the first current mirror circuit 14 is at the maximum.
4 is set to be less than the second constant current I2 (I4 <I2), whereby the control current Icont is set by the third constant current I6 and the non-zero current I7.
This is possible when the input control signal Vcont is minimum.

In the embodiment of FIG. 4, the control current Icont is set at the maximum value I2 and the minimum value I6 as shown by the line 60, as shown in FIG. The maximum and minimum values of the 12 gains are fixed.

FIG. 6 is an electric circuit diagram of another embodiment of the present invention. This embodiment is similar to each of the above-described embodiments, and corresponding parts are denoted by the same reference numerals. The amplifier 12 having a gain corresponding to the control current Icont is connected via a line 61 to a transistor Q2 of a logarithmic conversion circuit 13 which is a function generator. The constant current source 59 extracts a constant current I6 corresponding to the minimum value of the control current Icont as a part of the control current Icont.

FIG. 7 is an electric circuit diagram of another embodiment of the present invention. In the amplifier 12, an output signal Vout is derived from the collector of the transistor Q02. The logarithmic conversion circuit 13 is connected to the line 19.

FIG. 8 is a graph showing characteristics of the embodiment of the present invention shown in FIG. Input control signal Vcon
As the voltage at t is increased, the gain of amplifier 12 increases in a logarithmic function as shown by line 62. The line 63 shows the characteristic in the prior art described in connection with FIG. 27 described above, and only the gain proportional to the level of the input control signal Vcont is obtained, while the embodiment of FIG. The variable width ΔG of the gain can be increased.

FIG. 9 is an electric circuit diagram of another embodiment of the present invention. In this embodiment, the input control signal Vcon
The logic of t is reversed from the embodiment shown in FIGS. 7 and 8 described above. Portions corresponding to the above-described embodiment are denoted by the same reference numerals. The logarithmic conversion circuit 13a is connected to the amplifier 12 via the current mirror circuit 16. In FIG. 9, each component of the logarithmic conversion circuit 13 a is denoted by the same numeral with a suffix a added to a portion corresponding to each of the above-described embodiments.

FIG. 10 is a graph showing the operation of the embodiment shown in FIG. As shown by line 64,
As the voltage of the input control signal Vcont increases, the amplifier 1
The gain of 2 decreases with a logarithmic function. Reference numeral 65 indicates a characteristic in which the gain changes linearly in accordance with the level of the input control signal Vcont, as in the prior art described with reference to FIG. 27 described above. It is understood that, according to the embodiment of the present invention, the variable width ΔG of the gain can be made larger than the characteristic of the line 65.

FIG. 11 is an electric circuit diagram of another embodiment of the present invention. This embodiment is similar to the embodiment shown in FIGS. 9 and 10, and the corresponding parts are denoted by the same reference numerals, and current mirror circuit 16a corresponds to current mirror circuit 16 described above. The parts are indicated by the same numerals with the suffix a. Control current Ico of amplifier 12
The current nt is controlled by flowing a current through the line 34 of the logarithmic conversion circuit 13 according to the input control signal Vcont applied to the current mirror circuit 16a.

FIG. 12 is an electric circuit diagram of another embodiment of the present invention. This embodiment is similar to the embodiment described above with reference to FIGS. 9 and 10, and corresponding parts are denoted by the same reference numerals. It should be noted that, in this embodiment, the input format of the input control signal Vcont is changed from the configuration of FIG.
The variation in the gain of the amplifier 12 due to the variation in the base-emitter voltage V _{BE at} a can be reduced. For this reason, in the embodiment of FIG.
In addition to the current mirror circuit 16 and the logarithmic conversion circuit 13a, it further has a control transistor 66, an operational amplifier 67, and a control resistor R3. Operational amplifier 67
Has one input terminal 68 to which an input control signal Vcont is supplied, another input terminal 69 connected to the emitter of the control transistor 66, and an output terminal 70 connected to the base of the control transistor 66. An input control signal Vcont is provided between the connection terminal 23 and the connection terminal 71 of the input terminal 68 of the operational amplifier 67. The connection terminal 72 and the connection terminal 23 of the emitter of the control transistor 66, the input terminal 69 of the operational amplifier 67, and the control resistor R3
Is equal to the input control signal Vcont applied to the input terminal 68 (V1 = Vcont). Assuming that the current flowing from the logarithmic conversion circuit 13a to the collector of the control transistor 66 is I9 and the current flowing to the control resistor R3 is I8, Expression 10 is established.

I9 = I8 = Vcont / R3 (10) Accordingly, the current I9 of the logarithmic conversion circuit 13a depends on the voltage of the input control signal Vcont and the resistance value of the control resistor R3, and accordingly, the logarithmic conversion circuit The current I10 flowing through the collector of the transistor Q2a 13a is determined, and the control current Icont is determined by the current mirror circuit 16. Thus, in the embodiment shown in FIGS. 9 and 10 described above, the input impedance of the logarithmic conversion circuit 13a is low, so that an output voltage having poor load characteristics cannot be used as the input control signal Vcont as it is, but the embodiment shown in FIG. In the embodiment, the input impedance is increased by the operation of the operational amplifier 67, and the transistor Q
The gain of the amplifier 12 can be set without depending on 1a and the base-emitter voltage V _BE of the control transistor 66.

FIG. 13 is an electric circuit diagram of another embodiment of the present invention. The embodiment of FIG. 13 is the same as that of FIG.
By changing the order of the current mirror circuit 16 and the logarithmic conversion circuit 13a in the second embodiment, the current mirror circuit 1
The output of 6a is provided to the logarithmic conversion circuit 13.

FIG. 14 is an electric circuit diagram of another embodiment of the present invention. This embodiment is similar to the embodiment shown in FIGS. 7 and 8 described above, and corresponding parts are denoted by the same reference numerals. In this embodiment, the base-emitter voltage V _BE of the transistor Q1 of the logarithmic conversion circuit 13
The input form of the input control signal Vcont is changed in order to reduce the variation in the gain of the amplifier circuit 12 due to the variation in the input control signal Vcont. One end of a control resistor R4 is connected to one terminal Vcc of the DC power supply. Control transistor 74
Is connected to a connection point 75 at the other end of the control resistor R4.
Connected. The collector of the control transistor 74 is connected to the collector and base of the transistor Q1 of the logarithmic conversion circuit 13. Between the connection terminal 78 of one input terminal 77 of the operational amplifier 76 and the connection terminal 23,
An input control signal Vcont is provided. Operational amplifier 76
The other input terminal 79 is connected to the emitter of the control transistor 74 and thus to the connection point 75. The output terminal 80 of the operational amplifier 76 is connected to the base of the control transistor 74. By the operation of the operational amplifier 76,
The voltage V2 between the connection point 75 and the connection terminal 23 is equal to the voltage of the input control signal Vcont. Therefore, the voltage V3 between the connection point 75 and one terminal Vcc of the power supply is V3 = Vcc-V2 = Vcc. −Vcont (11) Therefore, the current flowing through the control resistor R4 is defined as I11.
The current flowing through the collector of the control transistor 74 is represented by I1
When it is set to 2, Expression 12 is established.

[0056]

(Equation 6)

The current I12 corresponds to the control current Icont, and thus the gain of the amplifier 12, by the operation of the logarithmic conversion circuit 13. Therefore, it is understood that the gain of the amplifier 12 does not depend on the variation of the base-emitter voltage V _BE of the transistor Q1.

FIG. 15 is an electric circuit diagram of still another embodiment of the present invention. Corresponding parts in the embodiments described above are denoted by the same reference numerals. The embodiment of FIG. 15 has the characteristics shown in FIG. 16, that is, the control current Icont changes in a plurality of stages according to the voltage of the input control signal Vcont, and the gain changes to a plurality of stages in accordance with this. , The control current Icont is determined by using an operational amplifier, and the accuracy of the gain can be increased.

A current mirror circuit 16 is connected to the amplifier 12 and extracts a control current Icont from a line 19. The collector of the first control transistor 83 is connected to the connection terminal 82 of one terminal Vcc of the power supply. The operational amplifier 84 has one input terminal 86 to which an input control signal Vcont is supplied from a connection terminal 85, and the other input terminal 87 is connected to the emitter of the first control transistor 83 at a connection point 88. Output terminal 84a of operational amplifier 84
Is connected to the base of the first control transistor 83.
A plurality of gain switching circuits A1 and A2 are interposed between the connection point 88 and the line 34 of the current mirror circuit 16. The gain switching circuit A1 includes a control resistor R11 and a second
It has a control transistor Q11, a reference voltage source VR1, and an operational amplifier AP1. One end of the control resistor R11 is connected to the emitter of the first control transistor 83, and thus to the connection point 88. Second control transistor Q1
One emitter is connected to the other end of the control resistor R11 at a connection point 89. This second control transistor Q11
Is connected to line 34 of current mirror circuit 16 to provide input current. The voltage of the reference voltage source VR1 is connected to one input terminal 90 of the second operational amplifier AP1, and the other input terminal 91 is connected to the second control transistor Q1.
Eleven emitters are connected at connection point 89. Output terminal 9
2 is connected to the base of the second control transistor Q11. Another gain switching circuit A2 has a configuration similar to the above-described gain switching circuit A1, and includes a control resistor R12.
And a second control transistor Q12, a reference voltage source VR2, and an operational amplifier AP2. In this embodiment, V
R1 <VR2.

Referring to the operating characteristics of the embodiment of FIG. 15 shown in FIG. 16, first, the operation of the first range W1 in which the voltage of the input control signal Vcont is 0 ≦ Vcont <VR1 (13) Will be described. Connection terminal 8
2 and 85, when an input control signal Vcont is applied, the connection point 88 associated with the operational amplifier 84 and the connection terminal 2
3 is equal to the voltage of the input control signal Vcont. Due to the operation of the operational amplifier AP1 of the gain switching circuit A1, the voltage between the connection point 89 and the connection terminal 23 is equal to the voltage of the reference voltage source VR1. Therefore, since the voltage at the connection point 88 is lower than the voltage at the connection point 89, the current I14 of the control resistor R11 is zero. Similarly, the voltage between the connection point 93 and the connection terminal 23 in the gain switching circuit A2 is equal to the reference voltage of the reference voltage source VR2, and the current I15 flowing through the control resistor R12 is also zero. Therefore, the current I16 (= I14 + I1) flowing through the line 34 of the transistor 32 of the current mirror circuit 16
5) is zero, the control current Icont is accordingly zero, and the gain of the amplifier 12 is zero.

Next, in the range W2 of FIG. 16, the following holds: VR1 ≦ Vcont <VR2 (14) Therefore, the current I14 of Expression 15 flows through the control resistor R11.

[0062]

(Equation 7)

In this range W2, the current I15 of the control resistor R12 is zero. Therefore, the control current Icont of the amplifier 12 is equal to the current I16 flowing through the line 34 by the operation of the current mirror circuit 16, and this current Icon
16 is a value equal to the current of Expression 15. This results in the characteristic shown by line 94 in FIG.

In the range W3 of FIG. 16, VR2 ≦ Vcont (16). At this time, the above equation 15 is satisfied, and equation 17 is also satisfied.

[0065]

(Equation 8)

The current I16 flowing through the line 34 of the current mirror circuit 16 is the sum of the currents I14 and I15. The control current Icont corresponding to the sum can be extracted from the amplifier 12. This results in line 9 in FIG.
5 are obtained.

According to the embodiment shown in FIG. 15, when the input control signal Vcont has an arbitrary value, for example, a desired gain G15 at V15, the base-emitter voltage of a large number of transistors 32, Q11, Q12 and the like used is changed. V
The advantage that the setting can be performed with high accuracy regardless of the characteristics of the _BE is achieved.

FIG. 17 is an electric circuit diagram of still another embodiment of the present invention. The embodiment of FIG. 17 is similar to the embodiment of FIGS. 15 and 16 described above, and corresponding portions are denoted by the same reference numerals. It should be noted that in this embodiment, three or more plural u gain switching circuits A1 to Au
Are interposed between the connection points 88 and 96. As a result, as shown in FIG. 18, the gain shown by lines 97, 98,... 99 can be changed for each of the reference voltage sources VR1 to VRu.

FIG. 19 is an electric circuit diagram of another embodiment of the present invention. The embodiment of FIG. 19 is similar to the embodiment of FIGS. 15 and 16 described above, and corresponding parts are denoted by the same reference numerals. In this embodiment, the first input current I17
In addition to the first current mirror circuit 16 for extracting the control current Icont of the amplifier 12 in response to the second input current Icon
A second current mirror circuit 100 that outputs a first input current I17 is provided in correspondence with. The second current mirror circuit 100 includes a pair of transistors 101 and 102
Having. An input control signal Vcont is provided between the input terminal 86 of the first operational amplifier 84 and the connection terminal 23. A plurality of (two in this embodiment) gain switching circuits A1 and A2 are interposed between the connection point 88 and the connection terminal 23.

In the embodiment shown in FIG. 19, a resistor R7 for gain operation is connected between connection point 88 and connection terminal 23.
Is connected. Thereby, the first control transistor 8
The current I18 from the emitter No. 3 branches and flows together with the plurality of gain switching circuits A1 and A2, and the flowing current is indicated by a reference numeral I19.

FIG. 20 is a graph showing characteristics of the embodiment shown in FIG. Each range W1, W2, W3 is the same as in FIG. In the range W1, the currents I14 and I15 do not flow through the gain switching circuits A1 and A2, but the current I19 always flows through the gain operating resistor R7.

[0072]

(Equation 9)

Therefore, the characteristic shown by line 103 in FIG. 20 is obtained.

In range W2 of FIG. 20, gain switching circuit A
1 flows through the control resistor R11, the current I14 of the current mirror circuit 100 is equal to the sum of the currents I14 and I19 (I18 = I1).
4 + I19), a current I17 corresponding to this is obtained, and a control current Icont is obtained.

In range W3 of FIG. 20, current I15 flows through control resistor R12 in another gain switching circuit A2, and thus current I1 of current mirror circuit 100 is supplied.
8 is the sum of these currents I14, I15 and I19 (I1
8 = I14 + I15 + I19), a current I17 corresponding to this flows, and a control current Icont is obtained, and the characteristic shown by the line 105 in FIG. 20 is obtained. Thus, the range W1 in which the voltage of the input control current Vcont is small
Also, the gain of the amplifier 12 can be changed. Therefore, the voltage range of the input control current for changing the gain can be widened.

FIG. 21 is an electric circuit diagram of still another embodiment of the present invention. This embodiment is similar to that of FIG.
20 and are similar to those in the embodiment of FIG. 20, and corresponding parts are denoted by the same reference numerals. In this embodiment, three or more u-th gain switching circuits A1 to Au are interposed between the connection point 88 and the connection terminal 23, and the characteristic shown by the broken line shown in FIG. Can be changed.

FIG. 22 is an electric circuit diagram of another embodiment of the present invention. This embodiment is similar to the embodiment shown in FIG. 15 and FIG. 16 described above, and corresponding portions are denoted by the same reference numerals. In this embodiment, the input control signal V in the embodiment shown in FIGS.
It has a configuration in which the logic of the voltage of cont is reversed, and as shown in FIG. 23, the gain is reduced as the input control signal Vcont increases. The control current Icon is applied to the line 19 of the amplifier 12 by the current mirror circuit 16.
t is extracted corresponding to the input current I25. A first control transistor 107 for flowing an input current I25 to the current mirror circuit 16 is provided. The collector of the control transistor 107 is connected to the commonly connected base and collector of the transistor 32 of the current mirror circuit 16 at a connection point 108. The operational amplifier 109
Input terminal 110 to which input control signal Vcont is applied
And another input terminal 111 connected to the emitter of the first control transistor 107, and an output terminal 112 connected to the base of the first control transistor 107. A plurality of (two in this embodiment) gain switching circuits B1 and B2 are interposed between the connection point 113 and the line 114 of one terminal Vcc of the power supply voltage, and a gain operation resistor R8 is interposed. . Gain switching circuit B1
Is a control resistor R21 having one end connected to the emitter of the first control transistor 107 at a connection point 113.
, A second control transistor Q21, and a reference voltage source VR.
1 and a second operational amplifier AP21. The second control transistor Q22 has an emitter connected to the other end of the control resistor R22, and has a collector connected to one terminal 114 of the DC power supply, and supplies an input current I25 to the current mirror circuit 16. In the second operational amplifier AP22,
The input terminal 115 is supplied with the voltage of the reference voltage source VR1, and the input terminal 116 is connected to the second control transistor Q2.
Connected to one emitter. The output terminal 117 is connected to the base of the second control transistor Q21.

Another gain switching circuit B2 is similarly constructed, and includes a control resistor R22, a second control transistor Q22, a reference voltage source VR2, and a second operational amplifier AP.
22. When the voltages of the reference voltage sources VR1 and VR2 are indicated by the same reference numerals, it is determined that VR1 <VR2 <Vcc.

In the current mirror circuit 16, in order for the transistor 32 to operate, the connection terminal 23 and the connection point 10
8 must be equal to or higher than the base-emitter voltage V _{BE of} the transistor 32. The base-emitter voltage V _BE is, for example, about 0.7V. First
The saturation voltage V _CE between the collector and the emitter of the control transistor 107 is, for example, about 0.2V.

The operation of the embodiment shown in FIG. 22 will be described with reference to FIG. When the input control signal Vcont is
The measurement is performed when it is in the range W11, that is, 0 ≦ Vcont <V _BE + V _CE (19). (V _BE + V _CE ) is, for example, about 0.9 V (= 0.7 + 0.2). The voltage at the connection point 113 is equal to the voltage of the input control signal Vcont by the operation of the operational amplifier 109. When the above expression 19 is satisfied, the first control transistor 107 and the transistor 32 of the current mirror circuit 16 do not operate, and therefore, the gain of the amplifier 12 cannot be obtained.

In the range W12 of FIG. 23, V _BE + V _CE ≦ Vcont <VR1 (20). At this time, the connection point 113 is connected to one terminal V of the DC power supply.
The voltage between cc and line 114 is (Vcc-Vco
nt). At this time, each gain switching circuit B1, B2
Currents I21, I2 flowing through the control resistors R21, R22
2 and the current I23 flowing through the gain operation resistor R8 are given by the following equation (2).
1 to 23.

[0082]

(Equation 10)

The current I 25 is supplied to the current mirror circuit 16.
(= I21 + I22 + I23), and the control current Icont is taken out of the amplifier 12 correspondingly.

In the range W13 of FIG. 23, VR1 ≦ Vcont <VR2 (24). At this time, equations (22) and (23) hold, and the input current I25 of the current mirror circuit 16 becomes (I22 + I2
3), the corresponding control current Icont is extracted.

In the range W14 of FIG. 23, the relationship is VR2 ≦ Vcont <Vcc (25). At this time, Expression 23 is established, the input current I25 of the current mirror circuit 16 corresponding to the current I23 flows, and the control current Icont is extracted corresponding to the current I23.

FIG. 24 is an electric circuit diagram of still another embodiment of the present invention. This embodiment is similar to FIG.
FIG. 19 is similar to the embodiment of FIG.
20 and are similar to those in the embodiment of FIG. 20, and corresponding parts are denoted by the same reference numerals. In this embodiment, the amplifier 12
A first current mirror circuit 16 for extracting the control current Icont corresponding to the first input current I17, and a second current mirror circuit 100 for outputting the first input current I17 corresponding to the second input current I18. Further, a first control transistor 123, a first operational amplifier 124, and a plurality (two in this embodiment) of gain switching circuits A1, A
2 are provided. The first operational amplifier 124 has one input terminal 125 to which the input control signal Vcont is supplied, the other input terminal 126 connected to the emitter of the first control transistor 123, and the first control transistor 1
23, and an output terminal 127 connected to the base.
The configuration of the gain switching circuits A1 and A2 is the same as in the above-described embodiment. The gain switching circuits A1 and A2 are interposed in parallel between a connection point 128 of the second current mirror circuit 100 and a connection point 129 of the emitter of the first control transistor 123. The voltage between the connection point 129 and the connection terminal 23 is equal to the input control signal Vc applied to the input terminal 125.
ont voltage. First control transistor 123
Saturation voltage V _CE between the collector and emitter of, for example, about 0.2V.

The operation of FIG. 24 will be described. Referring to the graph of FIG. 25, the voltage of input control signal Vcont is
When 11, that is, 0 ≦ Vcont <V _CE (26), the first control transistor 123 does not operate, and therefore the gain of the amplifier 12 cannot be obtained.

In the range W12 of FIG. It is. At this time, the current I26 flowing through the first control transistor 123 is the sum of the currents I21, I22, and I23 obtained in the same manner as in Expressions 21 to 23 described above. FIG.
Are the same as the ranges W13 and W14 described with reference to FIG.

In the embodiment shown in FIGS. 24 and 25, the voltage of input control signal Vcont used to change amplifier 12 is smaller than in the above-described embodiments of FIGS. 22 and 23. Can be extended to the range.

FIG. 26 is an electric circuit diagram when the variable gain amplifier 131 according to each embodiment of the present invention shown in FIGS. 1 to 25 is implemented as an AGC circuit in an intermediate frequency amplification stage in a radio receiver. is there. Input signal V
An intermediate frequency signal is provided as in, which is amplified and derived as an output signal Vout. This output signal Vo
ut is supplied to the detection circuit 132 and rectified, and an envelope waveform is obtained using the capacitor 133.
The signal is supplied to an inverting input terminal 136 of an operational amplifier 135 provided in 34. The reference voltage VR is applied to the non-inverting input terminal 137 of the operational amplifier 135. Operational amplifier 1
The output of the line 35 is supplied via the line 138 as the input control signal Vcont in each of the above-described embodiments.
8 is provided.

[0091]

According to the first aspect of the present invention, it is possible to widen the variable width of the gain of the amplifier using the function generator even if the change range of the voltage or current level of the input control signal Vcont is small. it can.

Further, according to the present invention, the maximum value of the control current Icont is limited by the second constant current of the second constant current source, so that the maximum value of the gain of the amplifier is accurately set. It is possible to prevent the gain from fluctuating due to the power supply voltage applied to the amplifier. Therefore, the maximum gain of the amplifier does not vary for each product sample of the variable gain amplifier.

According to the second aspect of the present invention, the minimum value of the control current Icont is limited by the third constant current of the third constant current source. To prevent the minimum gain from varying for each product sample of the variable gain amplifier.

According to the third aspect of the present invention, when the input current of the first current mirror circuit is maximum, the output current of the first current mirror circuit is equal to or more than the second constant current of the second constant current source. Since the mirror ratio of the first current mirror circuit, that is, the ratio between the output current and the input current of the first current mirror circuit, is set at the maximum, the input current of the first current mirror circuit is maximized. Output current I7 to zero, thereby controlling the amplifier control current Ic.
Ont is set to the third constant current I6 set by the third constant current source 59, and the minimum value can be reliably set.

According to the fourth aspect of the present invention, the input control signal Vcont is controlled by using a function generator having a logarithmic function.
, And the minimum value of the control current Icont is set by the constant current source. Therefore, even if the change range of the input control signal Vcont is small, the gain of the amplifier is controlled. Can be increased, and variation in the minimum gain for each product sample can be prevented.

According to the fifth aspect of the present invention, the logarithmic conversion circuit is connected to the amplifier, so that the variable width of the gain of the amplifier with respect to the change range of the level of the input control signal Vcont can be widened.

According to the sixth aspect of the present invention, it is possible to realize a variable gain amplifying apparatus in which the logic of the input control signal Vcont is inverted, as compared with the fifth aspect of the present invention. Is increased, the gain of the amplifier can be reduced. According to the present invention, as described with reference to FIG. 26 described above, the logic of the operational amplifier that supplies the input control signal Vcont to the variable gain amplifying device of the present invention can be configured to be non-inverted. The output of, for example, a radio circuit at the preceding stage can be received by the operational amplifier with high input impedance.

According to the seventh aspect of the present invention, a configuration is realized in which the order of the current mirror circuit and the logarithmic conversion circuit in the sixth aspect of the invention is reversed.

According to the eighth aspect of the present invention, the input control signal Vcont is supplied to one input terminal of the operational amplifier,
This makes it possible to reduce the variation in the gain of the amplifier due to the variation in the base-emitter voltage V _BE of the first transistor, as compared with a configuration in which the input control signal Vcont is directly applied to the first transistor of the logarithmic conversion circuit.

According to the ninth aspect of the present invention, a configuration is realized in which the order of the current mirror circuit and the logarithmic conversion circuit in the configuration of the eighth aspect is reversed.

According to the tenth aspect of the present invention, the input control signal Vcont is supplied to one input terminal of the operational amplifier, and the variation of the gain of the amplifier due to the variation of the base-emitter voltage V _BE of the first transistor of the logarithmic conversion circuit. Can be reduced.

According to the eleventh aspect of the present invention, by using a plurality of gain switching circuits, the input control signal Vco
The gain of the amplifier can be set with high accuracy at a slope corresponding to the voltage or current level of nt, and the gain of the amplifier can be largely changed even if the change range of the input control signal Vcont is small.

According to the present invention of claim 12, according to claim 11,
As compared with the present invention, the gain of the amplifier can be changed even in the range where the level of the input control signal Vcont is even smaller, and the input control signal that can be made variable in gain can be widened.

According to the thirteenth aspect of the present invention, a configuration in which the logic of the input control signal Vcont in the above-described twelfth aspect is reversed is realized, that is, the input control signal Vcot
As the level of nt is increased, the gain of the amplifier can be reduced.

According to the fourteenth aspect of the present invention, even if the input control signal Vcont is smaller than that of the thirteenth aspect of the present invention, the gain of the amplifier can be changed, and the input control signal can be varied. The signal level can be widened.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing a configuration of an embodiment of the present invention.

FIG. 2 shows a voltage of an input control signal Vcont and a control current Ic.
It is a graph which shows the relationship with ont.

FIG. 3 is a more specific electric circuit diagram of another embodiment of the present invention.

FIG. 4 is an electric circuit diagram of still another embodiment of the present invention.

FIG. 5 shows a voltage of an input control signal Vcont and a control current Ic.
It is a graph which shows the relationship with ont.

FIG. 6 is an electric circuit diagram of another embodiment of the present invention.

FIG. 7 is an electric circuit diagram of another embodiment of the present invention.

FIG. 8 is a graph showing characteristics of the embodiment of the present invention shown in FIG. 7;

FIG. 9 is an electric circuit diagram of another embodiment of the present invention.

FIG. 10 is a graph showing an operation of the embodiment shown in FIG. 9;

FIG. 11 is an electric circuit diagram of another embodiment of the present invention.

FIG. 12 is an electric circuit diagram of another embodiment of the present invention.

FIG. 13 is an electric circuit diagram of another embodiment of the present invention.

FIG. 14 is an electric circuit diagram of another embodiment of the present invention.

FIG. 15 is an electric circuit diagram of still another embodiment of the present invention.

FIG. 16 is a graph showing characteristics of the embodiment shown in FIG.

FIG. 17 is an electric circuit diagram of still another embodiment of the present invention.

FIG. 18 is a graph showing characteristics of the embodiment shown in FIG.

FIG. 19 is an electric circuit diagram of another embodiment of the present invention.

20 is a graph showing characteristics of the embodiment shown in FIG.

FIG. 21 is an electric circuit diagram of still another embodiment of the present invention.

FIG. 22 is an electric circuit diagram of another embodiment of the present invention.

FIG. 23 is a graph showing characteristics of the embodiment shown in FIG.

FIG. 24 is an electric circuit diagram of still another embodiment of the present invention.

FIG. 25 is a graph showing characteristics of the embodiment shown in FIG.

26 is an electric circuit diagram when the variable gain amplifying device 131 according to each embodiment of the present invention shown in FIGS. 1 to 25 is implemented as an AGC circuit in an intermediate frequency amplification stage in a radio receiver.

FIG. 27 illustrates a typical prior art.

[Explanation of symbols]

Reference Signs List 12 amplifier 13, 13a logarithmic conversion circuit 14 first current mirror circuit 15, 17 constant current source 16, 16a, 100 second current mirror circuit 23 the other terminal of DC power supply 27, 28, 30, 33 transistor 59 third Constant current source 66, 74 Control transistor 67, 76, 84, AP1, AP2 Operational amplifier 68, 86, 125 One input terminal 69, 87, 126 The other input terminal 70, 127 Output terminal 83, 107, 123 First Control transistor 124 First operational amplifier A1 to Au, B1, B2 Gain switching circuit AP21, AP22 Second operational amplifier I1 First constant current I2 Second constant current I6 Third constant current Icout Control current Q01, Q02 Transistor Vin input signal Vcc One terminal of DC power supply Vout output signal V out Input control signal VR1, VR2 Reference voltage source R1 First resistor R2 Second resistor R3 Third resistor R4, R11, R12, R21, R22 Control resistors R7, R8 Gain operation resistors Q1 First transistor Q2 Second transistor Q11 , Q12, Q21, Q22 Second control transistor

Claims (14)

[Claims] An amplifier having a gain corresponding to the control current Icont, a function generator whose output current increases according to a predetermined characteristic according to an increase in the level of the input control signal Vcont, a first current mirror circuit, A first constant current source for branching and supplying a predetermined first constant current to an output of the function generator and an input of the first current mirror circuit; and a second constant current source for deriving a control current Icont of the amplifier as an output.
And a second predetermined mirror circuit corresponding to the maximum value of the control current Icont.
And a second constant current source for branching and supplying the constant current to the output of the first current mirror circuit and the input of the second current mirror circuit. 2. The apparatus according to claim 1, further comprising a third constant current source that extracts a predetermined third constant current corresponding to the minimum value of the control current Icont as a part of the control current Icont. Variable gain amplifier. 3. The mirror ratio of the first current mirror circuit is:
3. The variable gain amplifying device according to claim 2, wherein the output current I4 flowing when the input current of the first current mirror circuit is maximum is equal to or larger than the second constant current I2. 4. An amplifier having a gain corresponding to the control current Icont, a function generator whose output current increases according to a predetermined logarithmic function according to an increase in the level of the input control signal Vcont, and a minimum value of the control current Icont. A variable gain amplifier, comprising: a constant current source for extracting a predetermined constant current corresponding to a value as a part of the control current Icont. 5. An input signal to be amplified is provided between the bases of a pair of transistors whose emitters are connected in common, and an output signal amplified from a collector of the transistor is provided between the bases of the transistors. A derived control current Icon from the commonly connected emitter
(b) a logarithmic conversion circuit, wherein the first resistor R1 and the second resistor R2 are one end of the first resistor R1 and one end of the second resistor R2. A second resistor R2 to which an input control signal Vcont is supplied, a collector and a base commonly connected to the other end of the first resistor R1, and an emitter connected to the other end of the second resistor R2. A second transistor having a base to which the base of the first transistor is connected, a collector connected to the commonly connected emitter of the amplifier, and an emitter connected to the one end of the second resistor. And a logarithmic conversion circuit having a transistor Q2. 6. A transistor having a pair of transistors whose emitters are commonly connected, an input signal to be amplified is provided between bases of these transistors, and an output signal amplified from a collector of the transistor is provided. A derived control current Icon from the commonly connected emitter
an amplifier having a gain corresponding to t; (b) a current mirror circuit for extracting the control current Icont according to the input current; and (c) a logarithmic conversion circuit, wherein a first resistor R1 and a second resistor R2 are provided. A second resistor R2 to which an input control signal Vcont is applied between one end of the first resistor R1 and one end of the second resistor R2; and a collector and a base commonly connected to the other end of the first resistor R1. A first transistor Q1 whose emitter is connected to the other end of the second resistor R2, and a base to which the base of the first transistor Q1 is connected. And a logarithmic conversion circuit having an emitter connected to the one end of the second resistor R2 and a second transistor Q2. 7. (a) A pair of transistors whose emitters are connected in common, an input signal to be amplified is provided between bases of these transistors, and an output signal amplified from a collector of the transistor is provided. A derived control current Icon from the commonly connected emitter
an amplifier having a gain corresponding to t; (b) a current mirror circuit for supplying an output current in response to the input control signal Vcont; and (c) a logarithmic conversion circuit, wherein a resistor, a collector and a base are common. , A first transistor having an emitter connected to one end of the resistor, a base connected to a base of the first transistor,
A logarithmic conversion circuit having a collector connected to the commonly connected emitter of the amplifier, and a second transistor having the emitter connected to the other end of the resistor. (A) An input signal to be amplified is provided between bases of a pair of transistors whose emitters are connected in common, and an output signal amplified from a collector of the transistor is provided between the bases of the transistors. A derived control current Icon from the commonly connected emitter
an amplifier having a gain corresponding to t; (b) a current mirror circuit for extracting the control current Icont in accordance with an input current; (c) a control transistor; and (d) an operational amplifier, wherein the input control signal , An input terminal connected to the emitter of the control transistor, and an output terminal connected to the base of the control transistor; and (e) the other of the operational amplifiers A control resistor R3 connected between the input terminal and one terminal of the power supply; (f) a logarithmic conversion circuit, a resistor having one end connected to the other terminal of the power supply; a collector and a base. A first transistor connected in common to the collector of the control transistor and having an emitter connected to the other end of the resistor; and a base connected to a base of the first transistor. ,
A variable gain amplifying device, comprising: a logarithmic conversion circuit that supplies the input current of the current mirror circuit from a collector and has a second transistor whose emitter is connected to the other terminal of the power supply. 9. A transistor having a pair of transistors whose emitters are commonly connected, an input signal to be amplified is provided between bases of these transistors, and an output signal amplified from a collector of the transistor is provided. A derived control current Icon from the commonly connected emitter
an amplifier having a gain corresponding to t; (b) a current mirror circuit for supplying an output current corresponding to the input current; and (c) a logarithmic conversion circuit, wherein the emitter resistance, the collector and the base are commonly used. A first transistor having an emitter connected to one end of the emitter resistor, a base connected to a base of the first transistor,
A logarithmic conversion circuit having a collector connected to the commonly connected emitter of the amplifier and an emitter connected to the other end of the emitter resistor; and (d) flowing the input current of the current mirror circuit. A control transistor; (e) an operational amplifier, one input terminal to which an input control signal Vcont is applied, the other input terminal connected to the emitter of the control transistor, and the base connected to the control transistor. And (f) a control resistor R6 connected between the other input terminal of the operational amplifier and a power supply. (A) A pair of transistors whose emitters are connected in common, an input signal to be amplified is provided between the bases of these transistors, and an output signal amplified from a collector of the transistor is provided. A control current Ico derived and taken out of said commonly connected emitter
(b) a control resistor R4 having one end connected to one terminal of the power supply; and (c) a logarithmic conversion circuit, one end of which is connected to the other terminal of the power supply. An emitter resistor connected in common, a collector and a base are connected in common, an output current from the current mirror circuit is applied, and a first transistor having an emitter connected to the other end of the emitter resistor; Has a base to which it is connected,
A logarithmic conversion circuit having a collector connected to the commonly connected emitter of the amplifier, and a second transistor having the emitter connected to the other end of the emitter resistor; and (d) connecting to the other end of the control resistor R4. A control transistor having an emitter connected thereto, and a collector connected to the collector of the first transistor of the logarithmic conversion circuit; and (e) one input terminal of the operational amplifier, to which an input control signal is applied; Variable gain amplifying device having an operational amplifier having the other input terminal connected to the emitter of the control transistor and an output terminal connected to the base of the control transistor. (A) An input signal to be amplified is provided between the bases of a pair of transistors whose emitters are connected in common, and an output signal amplified from a collector of the transistor is provided between the bases of the transistors. A control current Ico derived and taken out of said commonly connected emitter
an amplifier having a gain corresponding to nt; (b) a current mirror circuit for extracting the control current Icont corresponding to an input current; and (c) a first mirror having a collector connected to one terminal of a power supply.
A control transistor, (d) a first operational amplifier, one input terminal to which an input control signal is supplied, another input terminal connected to an emitter of the first control transistor, and a first control transistor. A first operational amplifier having an output terminal connected to the base of (e), and (e) a plurality of gain switching circuits, each of the gain switching circuits being (e1) one end connected to the emitter of the first control transistor. (E2) a second control transistor having an emitter connected to the other end of the control resistor, and a collector for providing an input current to the current mirror circuit; and (e3) a reference voltage source. (E4) one input terminal to which the voltage of the reference voltage source is applied; the other input terminal connected to the emitter of the second control transistor; (E5) the voltage of the reference voltage source for each gain switching circuit includes a mutually different gain switching circuit. Variable amplification device. 12. (a) A pair of transistors whose emitters are connected in common, an input signal to be amplified is provided between bases of these transistors, and an output signal amplified from a collector of the transistor is provided. A control current Ico derived and taken out of said commonly connected emitter
an amplifier having a gain corresponding to nt, and (b) the control current Icont corresponding to a first input current.
(C) a second current mirror circuit that outputs a first input current of the first current mirror circuit in response to a second input current; and (d) a second current mirror circuit that outputs a second current mirror circuit. (E) a first operational amplifier having a collector through which an input current flows; and (e) a first operational amplifier, one input terminal to which an input control signal is applied, and the other connected to an emitter of the first control transistor. (F) a plurality of gain switching circuits, wherein each of the gain switching circuits comprises (f1) a first operational amplifier. A control resistor having one end connected to the emitter of the control transistor, an emitter connected to the other end of the control resistor, and an input current to the second current mirror circuit. A second control transistor having a collector, (f3) a reference voltage source, and (f4)
One input terminal to which the voltage of the reference voltage source is applied;
(F5) a second operational amplifier having another input terminal connected to the emitter of the control transistor and an output terminal connected to the base of the second control transistor;
The voltage of the reference voltage source for each gain switching circuit includes a gain switching circuit different from each other, and (g) a gain operating resistor for branching and flowing a current from the emitter of the first control transistor. Variable gain amplifier. (A) An input signal to be amplified is provided between the bases of a pair of transistors whose emitters are connected in common, and an output signal amplified from a collector of the transistor is provided between the bases of the transistors. A control current Ico derived and taken out of said commonly connected emitter
an amplifier having a gain corresponding to nt, (b) a current mirror circuit for extracting the control current Icont corresponding to the input current, and (c) a first control transistor having a collector for flowing the input current to the current mirror circuit. (D) an operational amplifier, which is connected to one input terminal to which an input control signal is supplied, the other input terminal connected to the emitter of the first control transistor, and the base of the first control transistor. A first operational amplifier having an output terminal; and (e) a plurality of gain switching circuits, each gain switching circuit comprising: (e1) a control resistor having one end connected to the emitter of the first control transistor. And (e2) a second control transistor having an emitter connected to the other end of the control resistor and a collector for providing an input current to the current mirror circuit. (E3) a reference voltage source, (e4) one input terminal to which the voltage of the reference voltage source is applied, the other input terminal connected to the emitter of the second control transistor, and a second control transistor. (E5) the voltage of the reference voltage source for each gain switching circuit is different from each other, and (f) the first control And a gain operating resistor for branching and flowing a current to an emitter of the transistor. 14. (a) A pair of transistors whose emitters are commonly connected, an input signal to be amplified is provided between bases of these transistors, and an output signal amplified from a collector of the transistor is provided. A control current Ico derived and taken out of said commonly connected emitter
an amplifier having a gain corresponding to nt, and (b) the control current Icont corresponding to a first input current.
(C) a second current mirror circuit that outputs a first input current of the first current mirror circuit in response to a second input current; (d) a first control transistor; (E) a first operational amplifier, one input terminal to which an input control signal is applied, the other input terminal connected to the emitter of the first control transistor, and the base connected to the first control transistor. (F) a plurality of gain switching circuits, wherein each gain switching circuit has one end connected to the emitter of the (f1) first control transistor. A second control transistor having a resistor, (f2) an emitter connected to the other end of the control resistor, and a collector for providing an input current to the current mirror circuit; and (f3) a reference voltage source. (F4) one input terminal supplied with the voltage of the reference voltage source, the other input terminal connected to the emitter of the second control transistor, and the output terminal connected to the base of the second control transistor. And (f5) a voltage of a reference voltage source for each gain switching circuit includes a gain switching circuit different from each other.