JPH10117124A - Amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the amplifier whose dynamic range is wide regardless of an input current amplitude and from which a signal amplified with higher quality at a high gain is obtained. SOLUTION: A collector of a transistor(TR) 1 is connected to a base of a TR 2 via a gain adjustment section 13 and Feedback resistors Rf1 , Rf2 are connected between the base of the TR 1 and the gain adjustment section 13. The gain adjustment section 13 has a differential amplifier circuit 13A. Both one-terminals of the feedback resistors Rf1 , Rf2 are connected to the base of the TR 1. Furthermore, the other terminal of the feedback resistor Rf1 connects to an emittgr of a TR 5 and a base of a TR 7 and the other terminal of the feedback resistor Rf2 connects to an emitter of a TR 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier for converting an input current into a voltage in accordance with the magnitude of an input signal current, amplifying and outputting the voltage, and particularly to a preamplifier for optical communication.

[0002]

2. Description of the Related Art Information devices using light are increasing as a new means of information communication. An optical receiver on the light receiving side of this information device is provided with a light receiving element for converting an optical signal into an electric signal (current). The amount of light received by the light receiving element is weak, and tends to become weaker as the device becomes smaller, lighter, and lower in power consumption. In the optical receiver, a preamplifier is provided after the light receiving element to amplify the weak output from the light receiving element.
The preamplifier is a current / voltage converter that outputs an output signal from the light receiving element as a voltage corresponding to the magnitude of the current.
Generally, a preamplifier is required to have characteristics such as low noise, a wide dynamic range, a wide band, and a high gain.

[0003] An example of such a preamplifier is an impedance type amplifier. In this preamplifier, the output signal _Vout from the preamplifier is, for example, a current to be an input signal to the preamplifier I _in , and the base of the first-stage transistor indicating the gain of the pre-amplifier-the next stage. If the resistance value placed between the emitters of the transistor is _Rf ,

[0004]

## EQU1 ## V _out = −R _f · I _in (1) This type of preamplifier converts the input current into a voltage based on equation (1).

[0005]

By the way, the transmitting device emits light to the receiving device with a constant light intensity. However, for example, when the transmission distance of the information device is short, the device on the receiving side receives strong light. As a result, the light receiving element of the optical receiver on the receiving side generates a large current, and a large current is supplied from the light receiving element to a preamplifier provided downstream of the light receiving element. Even if such an input current is input to the preamplifier, it is necessary to prevent the first-stage transistor from performing a saturation operation so that the output voltage from the preamplifier becomes an accurate output. It is known that the gain, that is, the resistance value _Rf, should be reduced for this purpose, as is apparent from the equation (1).
When the gain is kept low and the input current is small, the output voltage from the preamplifier becomes small.

On the other hand, at the time of operation of the preamplifier, the amplifier itself emits noise of a certain level or more regardless of the magnitude of the input current, for example. Therefore, when the output voltage is small as described above, the level of noise with respect to the output signal relatively increases. Further, such a decrease in the amplitude of the output signal in the preamplifier is greatly affected by noise (particularly, thermal noise) generated in a peripheral circuit of the preamplifier. This means that the preamplifier degrades the S / N ratio of the output signal on the low input current side. If the gain is set so as to satisfy the amplification of the input signal from the large current region, the signal quality of the output signal obtained from the small input current region deteriorates and becomes unusable. However, the usable dynamic range of the preamplifier is reduced.

The present invention solves the above-mentioned drawbacks of the prior art, and provides an amplifier capable of obtaining a signal having a wide dynamic range, a high gain and a higher quality signal irrespective of the magnitude of an input current. The purpose is to do.

[0008]

According to the present invention, there is provided an amplifying device for converting an input current into a voltage in accordance with the magnitude of the input current, amplifying the output, and outputting the amplified voltage. The device includes a first transistor to which an input current is supplied, a second transistor connected to a collector of the first transistor, a collector resistor provided between a collector of the first transistor and a power supply, , A first feedback resistor for applying a negative feedback to the base of the first transistor, the collector of the first transistor being connected to the base of the second transistor, the device further comprising a base of the second transistor. Has a gain adjusting means connected in parallel to adjust the magnitude of the gain according to the magnitude of the input current,
The first feedback resistor is connected between the gain adjustment means and the base of the first transistor, and the device further comprises a second feedback resistor connected in parallel with the first feedback resistor. And

According to the amplifier of the present invention, the first transistor, the second transistor, the gain adjusting means and the first transistor
And the second feedback resistor is connected in parallel, the collector of the first transistor is connected to the base of the second transistor, and the gain adjusting means connected in parallel with the base of the second transistor is connected to the input terminal. The setting is such that the magnitude of the gain changes according to the current and is selected. Thereby, for example, the gain adjustment means selects at least a large gain when the input current is small, and reduces the gain when the input current is large, and adjusts the magnitude of the output voltage output from the amplifier. I am adjusting. With this adjustment, the amplifier device can be operated so that the output voltage is not buried in noise and the first transistor does not saturate.
A high-quality output voltage in which the influence of noise is suppressed over the input current range can be obtained. As a result, the amplifying device can have a wide dynamic range of the output voltage corresponding to the input current range.

Here, the gain adjusting means has a third transistor and a fourth transistor for alternately amplifying, and the emitter of the third transistor and the emitter of the fourth transistor are grounded at one end. A differential amplifier connected to the other end of the constant current source, a fifth transistor vertically connected to a third transistor of the differential amplifier, and a vertically connected fourth transistor of the differential amplifier. A sixth transistor, and a seventh transistor for applying an output to the base of the third transistor. One end of the first and second feedback resistors is connected to the base of the first transistor. The other end of the first feedback resistor is connected to the output of the fifth transistor and the base of the seventh transistor, and the other end of the second feedback resistor is connected to the output of the sixth transistor. Is connected, it is preferable that the base of the fourth transistor is configured as a reference voltage is applied.

With this configuration, the gain adjusting means divides the range of the input current into three current regions and selectively sets and adjusts the gain in accordance with the operation of the differential amplifying means in the gain adjusting means. ing. The gain of each region is determined by a relationship based on the values of the first feedback resistor and the second feedback resistor in accordance with the on / off state of the differential amplifier and the change in the impedance state of the fifth and sixth transistors. .
The value of each feedback resistor is preferably selected so that the gain of each region of the input current is appropriate. That is, for example, it is preferable to set a large gain in a region where the input current is small and to set a small gain in a region where the input current is large.

Further, in the amplifying device, the gain adjusting means is connected in multiple stages between the first transistor and the second transistor,
Two feedback resistors provided for each stage of the gain adjusting means may be connected to the base of the first transistor. According to this configuration, the range in which the input current can be handled can be expanded, and the dynamic range of the output voltage can be expanded accordingly. In addition, an amplification device that narrows and finely sets an input current range divided by each gain adjusting means and outputs the output current as an output voltage that is more accurately amplified with respect to the input current than a single-stage configuration when configured in multiple stages. Can be provided.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an amplifying apparatus according to the present invention.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the amplifying device according to the present invention. The amplifying device according to the present invention is used, for example, as a preamplifier of an optical receiver for optical communication. In this embodiment, a case will be described in which an amplifying device is applied as the preamplifier. This preamplifier has a current / voltage conversion function of outputting a voltage proportional to a current supplied as an input signal. A circuit that provides this function includes a so-called transimpedance amplifier circuit. As an example of a transistor circuit, the basic configuration of this circuit includes two transistors Tr1 and T
and r2, and the collector resistor R1, and the feedback resistor R _f1, the emitter
A follower emitter resistor R4 is included. The output impedance of the transistor Tr2 is reduced by performing an emitter follower operation.

The preamplifier 10 of the present embodiment further includes a gain adjuster 13 for adjusting the magnitude of the gain in accordance with the magnitude of the input current, in addition to the configuration of the transimpedance amplifier circuit.
And a feedback resistor _Rf2 newly provided to generate a gain corresponding to the adjustment of the gain adjustment unit 13.

The connection relationship will be described more specifically.
The preamplifier shown in the figure has a photodiode for photoelectric conversion.
The input current from PD is applied to transistor Tr1 via input terminal 11.
Is supplied to the base. The transistor Tr1 is an NPN transistor in the present embodiment, and its transistor
One end of a feedback resistor _Rf1 is connected to the base of Tr1. Similarly, an NPN transistor Tr2 is connected to the collector of the transistor Tr1. Collector resistance
R1 is provided between the collector side of the transistor Tr1 and the power supply terminal 12. The feedback resistor R _f1 is the transistor Tr1
Apply negative feedback to the base side of. Furthermore, the transistor Tr
1 is connected to the base of the transistor Tr2, and the gain adjuster 13 is arranged in parallel with the base of the transistor Tr2, and adjusts the magnitude of the gain according to the magnitude of the input current. Another feedback resistor _Rf2 is connected in parallel with the feedback resistor _Rf1 connected between the gain adjustment unit 13 and the base side of the transistor Tr1.

The gain adjuster 13 has an emitter of an NPN transistor Tr3 and an emitter of an NPN transistor Tr4 connected to the other end of a constant current source 13a having one end grounded via resistors R3 and R4, respectively. A differential amplifier circuit 13A,
NP vertically connected to transistor Tr3 of differential amplifier circuit 13A
An N-type transistor Tr6 vertically connected to an N-type transistor Tr5 and a transistor Tr4 of the differential amplifier circuit 13A.
And an NPN transistor Tr7 for applying an emitter follower output to the base of the transistor Tr3. A reference power supply _Vref for applying a reference voltage BV is connected to the base side of the transistor Tr4 of the differential amplifier 13A.

The feedback resistors R _f1 and R _f2 that determine the gain of the preamplifier 10 have one ends connected to the base of the transistor Tr1, as described above. Also, feedback resistor
The other end of R _f1 is connected to the emitter of transistor Tr5 and the base of transistor Tr7, while the feedback resistor R
The other end of _f2 is connected to the emitter of transistor Tr6.

Here, a more detailed connection between the elements will be described. The emitter of the transistor Tr1 - Between the ground, without greatly changing the signal voltage, the level shift diode D _n to shift the DC potential of the signal line is provided. Level shifting diode D _n is allowed to plural vertical connection toward the ground side of the cathode side. Level shifting diode D _n is the anode of the zener diode in view of the displacement amount of DC potential may be disposed toward the ground. The level shift diode D _n is set the offset voltage for the output voltage. Therefore, this offset voltage defines the lower limit of the dynamic range of the output voltage. Further, one ends of emitter resistors R4 and R5 are connected to the emitters of the transistors Tr2 and Tr7, respectively. The other ends of the emitter resistors R4 and R5 are both grounded. The preamplifier 10 is a circuit operable with a single power supply, and the power supply terminal 12 includes a cathode of a photodiode PD, one end of a collector resistor R1, and a transistor.
Connected to the collectors of Tr2, Tr5, Tr6.

Next, the operation of the preamplifier 10 will be described with reference to FIG.
This will be briefly described with reference to FIG. Here, the offset voltage to the output voltage by the level shift diode D _n denotes the output voltage with respect to current inputted ignored. In the preamplifier 10, the magnitudes of the feedback resistors R _f1 and R _f2 are set so as to have a relationship of R _{f1 ≫R f2} . When light enters the photodiode PD, the photodiode PD converts the light into a current according to the intensity of the incident light.

[0021] When the input current corresponding to the input signal is small, for example in the range of the current I ₁ from zero, firstly,
The transistor Tr7 of the gain adjustment unit 13 is turned on. The transistor Tr7 functions as a switching element for starting the operation of the differential amplifier circuit 13A. When the transistor Tr7 is turned on, the transistor of the differential amplifier circuit 13A is turned on.
Tr3 turns on. At this time, the transistor Tr5 vertically connected to the transistor Tr3 has a low impedance. On the other hand, the transistor Tr4 is still in the off state, and the transistor vertically connected to the transistor Tr4
Tr6 has high impedance. Current equal to the input current I _in is to flow only feedback resistor R _f1 by the negative feedback effect in this situation. Therefore, the input current
When I _in is _in the range of 0 <I _in <I ₁ , the gain (transimpedance gain Z _t ) by the operation of the gain adjustment unit 13 is R _f1 (see FIG. 2A). Therefore, the output voltage V
_out is obtained by substituting R _f1 selected by the gain adjustment unit 13 for the input current I _in and the gain Z _t .

[0022]

## EQU2 ## V _out = −R _f1 · I _in (2) Expressed in absolute value of the output voltage obtained from the relationship of formula (2), the input current I _in of FIG. 2 (b) 0 <output voltage in the range of I _in <I ₁ is larger the slope of the line to the right up Is represented.

[0023] Referring now current I _in is greater than the current value _{I 1 (I 1 <I in} ), the transistors Tr3, Tr4 is both turned on. At this time, a current equal to the input current I _in flows through the feedback resistors R _f1 and R _f2 toward the base of the transistor Tr1.
Thus, the transimpedance gain Z _t by the negative feedback effect of the feedback resistor R _f1, R _f2 which is connected in parallel R _f1 ‖R _f2,
That is, R _f1 R _f2 / (R _f1 + R _f2 ). Also, the output voltage V
_out is the reference voltage V applied to the base of the transistor Tr4
It becomes the same voltage as _ref . The output voltage becomes constant output amplitude both transistors are turned on until the current value I ₂ followed (see Figure 2 (b)).

Next, when an input current I _in larger than the current value I ₂ is input (I ₂ <I _in ), the transistor of the gain adjustment unit 13
The base voltage of Tr3 becomes lower than _Vref . As a result, the operation of the transistor Tr3 is turned off, and the transistor Tr3 is turned off.
Tr5 becomes high impedance. On the other hand, at this time, the transistor Tr4 remains on, and the vertically connected transistor Tr6 has a low impedance. Transistor Tr
Current equal to the input current I _in toward the first base flows only feedback resistor R _f2. Therefore, this input current I _in
The gain adjustment section is caused by the negative feedback effect of the feedback resistor R _f2 through which
13 selected gain, i.e., the transimpedance gain Z _t becomes R _f2. As described above, since the gain is small with R _f2 (the relationship is R _{f1 ≫R f2} ), as is clear from FIG. 2, the slope of the output voltage V _out is such that the input current range is 0 <I _in <I ₁ . The output voltage slope is smaller than R _f1 . However, since the input current _Iin is large, the absolute value of the output voltage _Vout is obtained as a large value as shown in FIG.

As a result, the input current is in a smaller range (I _in <I ₁ ) than in the case of the circuit configuration in which the voltage is converted corresponding to the entire current range input with one gain. However, since the gain adjustment unit 13 selects the gain R _f1 and obtains a large output voltage, the output voltage can be set to a high S / N ratio with respect to noise generated in the preamplifier 10. By lowering the lower limit of usable input current,
The dynamic range of the output signal can be extended downward. Further, in a range where the input current is large (I ₂ <I _in ), the gain adjustment unit 13 can select the gain to be a small value of R _f2 so that the transistor Tr1 is not saturated.
Therefore, an appropriate output signal can be obtained even if a large input current is input, and the output signal can be extended to the upper limit side of the dynamic range.

As described above, by selecting an appropriate gain in accordance with the magnitude of the input current, the input range of the input current is widened, and the dynamic range of the output voltage with respect to the input current is widened, and the output is obtained. Signal S /
The N ratio can also be improved. The preamplifier 10 can output a high-quality signal.

Next, a modified example of the preamplifier 10 is shown in FIG.
This will be described with reference to the circuit configuration of FIG. In this case, the preamplifier 10 includes n gain adjustment units 131, 131 between the transistor Tr1 and the transistor Tr2.
132, ..., 13n are connected vertically (n is a natural number). The circuit elements of the gain adjustment units 131, 132,..., 13n use the same elements as the circuit elements of the gain adjustment unit 13 shown in FIG. The reference numerals of the circuit elements in each stage are the same as those of the common circuit elements, and are indicated by the suffix indicating the number of stages. The difference between the configurations of the gain adjustment units 131, 132,..., 13n in each stage will be described. For example, transistors Tr4 ₁ , Tr4 ₂ ,.
_n (not shown) applied to the bases BV ₁ , B
V ₂ ,..., BV _n (not shown) are reference voltages V _ref1 ,
V _ref2 ,..., V _refn (not shown). The magnitude of this reference voltage increases in the order of V _ref1 <V _ref2 <..., V _refn . In addition, each gain adjuster 131, 13
2, ..., two feedback resistors to 13n (R _f11 and R _f21), (R _f12
And R _f22 ),..., (R _f1n and R _f2n ) (not shown) are connected in parallel. The size of the feedback resistors of each stage, R _f11 >> R
_{f21, R f21 = R f12 »R} f22, is set so as to maintain a relationship that ....

[0028] Therefore, the operation of the general gain controller and the previous feedback resistor pairs are longitudinally connected preamplifier 10, transimpedance gain with increasing input current I _in through each stage as shown in FIG. 4 tends to Z _t is gradually decreased (see Figure 4 (a)). On the other hand, the output voltage V _out as the input current I _in increases gradually increases every time through the respective stages (see Figure 4 (b)). In more detail, when the input current I _in the transistors used in the differential amplifier circuit of the gain adjusting section in general there stage is both turned on is supplied, the input current I _in transimpedance gain Z with increasing _t decreases due to the effect of the feedback resistors connected in parallel. At this time, the output voltage _Vout becomes the same as the reference voltage set in this stage, and a constant level voltage is output. In FIG. 4B, for example, the current values I ₁ -I ₂ , I ₃ -I ₄ ,
The output voltages V _out for the sections of I ₅ -I ₆ , I ₇ -I _8, ... _Are V _ref1 , V _ref2 , V _ref3 , V _ref4,. When the transistors in the differential amplifier circuit are in other states,
Although not described in detail by taking the transimpedance gain Z _t is one value of the feedback resistor is set in each stage in accordance with the state of the transistor in the differential amplifier circuit, the output voltage V
_out is increased to the _upper right.

By the way, a small input current I _in, for example, to convert a range from zero to the current value I ₁ to a voltage,
It is preferable that the value R _f11 of the feedback resistor that exhibits the effect of the feedback resistor by the first-stage gain adjustment unit 131 be set to a particularly large value, as in the above-described embodiment. As a result, even if the noise of the preamplifier 10 and the thermal noise around the circuit occur, the input signal having a small signal is transimpedance gain _Zt.
The signal can be sufficiently amplified twice, and the S / N ratio of the output signal can be improved. The value of the feedback resistor provided for each of the following stages should be set while paying attention so that the transistor Tr1 in FIG. 3 is not saturated.

By setting a plurality of sets of gain adjusters and feedback resistors in this manner, the preamplifier 10 expands the dynamic range of the output voltage _Vout , and outputs an output signal corresponding to an input signal more than in the above-described embodiment. Can be treated as a smooth relationship, and a more accurate output can be obtained.

In these embodiments described above, the NPN
Although a transistor of the type is used, the present invention is not limited to this, and a PNP transistor, a field effect transistor (FET), or the like may be used, and the same effects as those of the embodiments can be obtained. Further, in the present embodiment, the configuration example in which the photodiode PD and the preamplifier 10 are combined as the light receiving element has been described, but the present invention is not limited to the present embodiment, and the configuration in which the photodiode PD is combined with the amplifying device is used. Can be applied. As another application example, there is a combination with an amplifying device using an avalanche photodiode APD instead of the photodiode PD by adding an external high voltage generating circuit. By this combination, an optical receiver having an ultra-high sensitivity and a wide dynamic range and an optical receiving system using the optical receiver can be configured.

[0032]

As described above, according to the present invention, the gain according to the input current is selected by the operation of the gain adjusting means, and the value of the feedback resistor connected in parallel according to the selection is used as the gain.
By obtaining the output voltage as a product of the input current and the gain according to the setting, an output voltage adjusted with respect to the input current is obtained. Also, for example, by using a large gain in a region where the input current is small and using a small gain in a region where the input current is large, an output signal from this amplifying device has a wide dynamic range and a high S / N ratio. Can be a signal.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of an amplifying device according to the present invention.

FIG. 2 is a graph showing a relationship between a transimpedance and an output voltage with respect to an input current in the circuit shown in FIG.

FIG. 3 is a circuit diagram showing a configuration of a modified example of the amplifying device shown in FIG.

FIG. 4 is a graph showing a relationship between a transimpedance and an output voltage with respect to an input current in the circuit shown in FIG. 3;

[Explanation of symbols]

10 Preamplifier 13 Gain adjuster 13A Differential amplifier 13a Constant current source BV Reference power supply Tr1 to Tr7 NPN transistor R _f1 , R _f2 Feedback resistance

Claims (3)

[Claims] 1. An amplifying device for converting an input current into a voltage according to the magnitude of the input current, amplifying and outputting the voltage, the device comprising: a first transistor to which the input current is supplied; A second transistor connected to a collector of the first transistor, a collector resistor provided between a collector of the first transistor and a power supply, and a second transistor for applying a negative feedback to a base of the first transistor. 1
Wherein the collector of the first transistor and the base of the second transistor are connected, and the device is further connected in parallel to the base of the second transistor to reduce the magnitude of the input current. The first feedback resistor is connected between a base of the gain adjustment unit and a base of the first transistor, and the device further includes a gain adjustment unit that adjusts a magnitude of the gain in accordance with the gain. An amplifying device having a second feedback resistor connected in parallel to the first feedback resistor. 2. The amplifying device according to claim 1, wherein said gain adjusting means includes a third transistor and a fourth transistor for alternately amplifying.
Differential amplifying means having an emitter of the third transistor and an emitter of the fourth transistor connected to the other end of a grounded constant current source at one end; A fifth transistor vertically connected to the third transistor, a sixth transistor vertically connected to the fourth transistor of the differential amplifying means, and an output applied to a base of the third transistor. The seventh
And one end of the first and second feedback resistors is connected to the first feedback resistor.
The other end of the first feedback resistor is connected to the output of the fifth transistor and the base of the seventh transistor, and the other end of the second feedback resistor is connected to the base of the fifth transistor. An amplifier device connected to an output of a sixth transistor, wherein a reference voltage is applied to a base of the fourth transistor. 3. The amplifying device according to claim 1, wherein said gain adjusting means is connected in multiple stages between said first transistor and said second transistor, and provided for each of said gain adjusting means in each stage. 2. An amplifying device, wherein two feedback resistors are connected in parallel with a base of the first transistor.