JPH05183362A - Alc circuit - Google Patents

Abstract

PURPOSE:To prevent a level fluctuation of an output signal due to a change in the ambient temperature in the ALC circuit employing a diode for its detector. CONSTITUTION:The ALC circuit provided with a variable gain amplifier 1, a detector 7 including a diode 2, a reference voltage source 5 and a differential amplifier circuit 6 is provided with a diode 9 of the same quality as the diode 2 of the detector 7 and with an analog adder 8 extracting a junction voltage of the diode 9 and adding it to the voltage detected by the detector 7. The fluctuation in the junction voltage of the diode 2 is cancelled by adding the junction voltage of the diode 9 to an output voltage of the detector 7 to eliminate level fluctuation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ALC circuit which keeps the output level of an amplifier constant regardless of the gain fluctuation of the amplifier and the input signal level. It relates to an ALC circuit that keeps it constant.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram of an example of a conventional ALC circuit. This ALC circuit amplifies an input signal e _in and outputs an output signal e _out, and a variable gain amplifier 1 capable of controlling a gain by a control voltage or a current,
A detector 7 configured by a diode 2 (junction voltage V _F ), a capacitor 3 and a resistor 4 for detecting the level of the output signal e _out as a voltage E ₁ , and a reference voltage source 5 for generating a reference voltage E ₂ . Potential difference Δ between voltage E ₁ and reference voltage E ₂
The differential amplifier 6 controls the gain of the variable gain amplifier 1 by the output voltage E ₃ or the output current I ₁ based on E ₀ .

Here, the voltage E ₁ is a voltage appearing across the capacitor 3 forming the detector 7. The detector 7 charges the capacitor 3 after the output signal e _out is rectified by the diode 2. As a result, the peak voltage E _P of the output signal e _out is held at both ends of the capacitor 3, but the electric charge of the capacitor 3 is gradually discharged by the resistor 4 and output to both ends of the capacitor 3 due to the balance between charging and discharging. Signal e
The peak voltage E _{P of out} appears successively, and this is the output signal e _out.
It is detected as a level sensitive voltage E ₁ . However, due to the junction voltage V _F of the diode 2, the capacitor 3 is actually
Of the output signal e _out is lower than the peak power E _P of the output signal e _out by the junction voltage V _F of the diode 2, and E ₁ = E _P −V _F (1)

Now, when the level of the output signal e _out fluctuates due to the fluctuation of the level of the input signal e _in , the voltage E ₁ changes accordingly, so that the potential difference ΔE ₀ changes. Then, the differential amplifier 6 obtained by amplifying this potential difference ΔE ₀
Output voltage E ₃ or output current I ₁ of this output signal e
Variable gain amplifier 1 so as to mitigate fluctuations in _out level
Is controlled to return the level of the output signal e _out to the preset target value, the balance is maintained at the point where the potential difference ΔE ₀ and the gain of the variable gain amplifier 1 are balanced.

Here, there is always a potential difference ΔE ₀ between the input terminals of the differential amplifier 6 in order to obtain the voltage E ₃ or the current I ₁ that determines the gain of the variable gain amplifier 1, but the differential amplifier 6 If the gain of is sufficiently large, the potential difference ΔE ₀ becomes a value that is sufficiently small with respect to the voltages E ₁ and E ₂ , so E ₁ −E ₂ = ΔE ₀ ≈0 and always consider E ₁ = E ₂ (2) can be made to (1) and _{(2) E P -V F =} E 2 ... (3) becomes the state is always maintained from the equation. That is, the output signal e
The level of _out is always maintained at a value (target value) at which the peak voltage E _P of the output signal e _out becomes E _P = E ₂ + V _F.

[0006]

[Problems to be Solved by the Invention] Such a conventional AL
The C circuit, the level of the output signal e _out is the output signal e _out
Is maintained at a value such that the peak voltage E _P thereof is equal to the sum of the reference voltage E ₂ and the junction voltage V _F of the diode 2. On the other hand, in general, the junction voltage of the diode has a property of remarkably changing due to the temperature change. Therefore, when the ambient temperature changes, the junction voltage V _{F of the} diode 2 changes, which causes the output signal e _out to be kept constant. This causes a problem that the peak voltage E _{P of the} output signal E _out fluctuates. An object of the present invention is to provide an ALC circuit that can prevent the level fluctuation of the output signal even when the ambient temperature changes.

[0007]

According to the present invention, an ALC circuit including a variable gain amplifier, a detector including a diode, a reference voltage source, and a differential amplifier is the same as the diode forming the detector. A diode of a type and an analog adder for taking out a junction voltage value of the diode and adding it to the voltage value detected by the detector are additionally provided.

[0008]

[Function] By adding the junction voltage of the diode of the same type as the diode forming the detector to the output voltage of the detector, the fluctuation of the junction voltage of the diode forming the detector is canceled and the output signal Eliminates level fluctuations in.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the ALC circuit of the present invention, and the same parts as those of the ALC circuit shown in FIG. In this configuration, in addition to the configuration of FIG.
Analog adder 8 and diode 2 that constitutes detector 7
The same type of diode 9 is added, and a resistor 10 and a voltage source 11 for generating a junction voltage are added to both ends of the diode 9. The cathode of the diode 9 is the voltage source 1
1 to the negative terminal of which the anode is connected to the resistor 10
The other end of 0 is connected to the positive terminal of the voltage source 11. As a result, a current flows through the diode 9 and a junction voltage V _F0 is generated across the diode 9. Further, the analog adder 8 adds the junction voltage V _F0 to the voltage value output from the detector 7 and outputs it to the differential amplifier 6.

Next, the operation of this embodiment will be described. Also in this circuit, the ALC operation is maintained as in the circuit of FIG. 2 by the equation (2), that is, the state of E ₁ = E ₂ (2). However, here, E ₁ is equal to the voltage value (E _P −V _F ) output from the detector 7 by the diode 9
Since it has a value obtained by adding the junction voltage V _F0 of, the following is obtained: E ₁ = (E _P −V _F ) + V _F0 (4)

From the equations (2) and (4), E _P −V _F + V _F0 = E _{2, that} is, in the present embodiment, E _P = E ₂ + (V _F −V _F0 ) (5) Is dripping

Here, since the diode 2 and the diode 9 are of the same type, the characteristics of changes in the junction voltages V _F and V _F0 with respect to temperature are the same, and V _F −V _F0 = 0 ( 6) holds. Therefore, from equations (5) and (6), E _P = E ₂ .

[0013] That is, the level of the output signal e _out in the present embodiment is kept at a level such as peak voltage E _P of the output signal e _out becomes equal to the reference voltage E ₂ generated by the reference voltage source 5 , The junction voltage V _{F of the} diode as the ambient temperature changes
Output signal e _out caused by a change in
Level fluctuations are eliminated.

[0014]

As described above, according to the present invention, the junction voltage generated in the diode of the same type as the diode constituting the detector is added to the output voltage of the detector. There is an effect that it is possible to obtain an ALC circuit in which the fluctuation of the output signal level due to the change is extremely small.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of an ALC circuit of the present invention.

FIG. 2 is a block diagram of an example of a conventional ALC circuit.

[Explanation of symbols]

 1 variable gain amplifier 2 diode 5 reference voltage source 6 differential amplifier 7 detector 8 analog adder

Claims (1)

[Claims] 1. A variable gain amplifier capable of controlling gain by voltage or current, a detector including a diode, a resistor, and a capacitor for detecting an output signal level of the variable gain amplifier as a voltage value, and the detector. , A diode of the same type as that of the diode, an analog adder that extracts the junction voltage value of this diode and adds it to the voltage value detected by the detector, a reference voltage source, and one input terminal The output voltage from the analog adder is applied to the other input terminal, the reference voltage from the reference voltage source is applied to the other input terminal, and the output voltage or current obtained by amplifying the potential difference between the two causes the variable gain amplifier A differential amplifier for controlling gain
LC circuit.