JP2000013149A - Amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an amplifier circuit by which a high output dynamic range is obtained even in the case that the output range of an amplifier is deteriorated due to the dispersion of operating ambient temperature of element characteristics. SOLUTION: A capacitor 2 is connected to an input terminal 1 and a clamp circuit 4 is connected to the capacitor 2. Furthermore, an amplifier 6 that receives a signal outputted from the clamp circuit 4 is connected to the clamp circuit 4. An output terminal 3 is connected to the amplifier 6. A signal outputted from the amplifier 6 is given to the output terminal 3 and fed back to the clamp circuit 4 as a feedback signal 9. That is, a feedback clamp circuit is composed of the clamp circuit 4 and the amplifier 6. Moreover, an electric potential 10 decided at an output stage of the amplifier 6 becomes a clamp potential of the clamp circuit 4. Furthermore, a constant voltage source 5 is connected to the amplifier 6 to decide the reference potential 8 of the amplifier 6 by the source 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit having a feedback clamp circuit for clamping and outputting a signal while feeding it back, and more particularly to an amplifier circuit capable of obtaining a large effective output dynamic range.

[0002]

2. Description of the Related Art In recent years, there are various amplifier circuits, and there is an amplifier having a feedback clamp circuit for outputting an amplified signal by clamping the potential of an output signal while applying feedback. FIG. 4 is a block diagram showing a conventional amplifier circuit.

In a conventional amplifier having a feedback clamp circuit, a capacitor 32 is connected to an input terminal 31, and a clamp circuit 34 is connected to the capacitor 32. Further, an amplifier 36 to which a signal output from the clamp circuit 34 is input is connected to the clamp circuit 34. The output terminal 33 is connected to the amplifier 36. The signal output from the amplifier 36 is output to an output terminal 33.
, And is fed back to the clamp circuit 34 as a feedback signal 39. That is, the clamp circuit 34 and the amplifier 36 constitute a feedback clamp circuit. Further, a constant voltage source 35 is connected to the clamp circuit 34 and the amplifier 36, and the clamp potential 37 of the clamp circuit 34 and the reference potential 38 of the amplifier 36 are determined by the constant voltage source 35.

In an amplifier circuit having a conventional feedback clamp circuit configured as described above, an amplifier 3
The constant voltage source 35 determines the reference potential 38 of No. 6. The clamp circuit 34 converts the signal input thereto into a constant voltage source 35
Is clamped (held) to the potential 37 determined by the above and output. The amplifier 36 amplifies the signal output from the clamp circuit 34 and outputs the amplified signal to the output terminal 33 as an output signal. At this time, the amplifier 36 feeds back a part of the output signal to the clamp circuit 34 as a feedback signal 39. In this manner, the conventional amplifier circuit outputs the output signal clamped at the predetermined potential 37 from the output terminal 33.

[0005]

However, when the power supply voltage, operating environment temperature, element characteristics, and the like of the amplifier 36 vary, the output dynamic range remarkably fluctuates, and an effective output dynamic range cannot be obtained. Therefore, there is a problem that a sufficiently large gain cannot be obtained and an output signal having a sufficiently large amplitude cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an amplifying circuit capable of obtaining a large output dynamic range even when the output range of an amplifier is degraded due to variations in operating environment temperature or element characteristics. The purpose is to provide.

[0007]

SUMMARY OF THE INVENTION An amplifier circuit according to the present invention includes a clamp circuit for holding an input signal at a clamp potential and outputting the same, amplifying a signal output from the clamp circuit, and feeding back the signal to the clamp circuit. Wherein the clamp potential is determined in relation to an output potential at an output stage of the amplifier.

In the present invention, since the clamp potential is determined in relation to the output potential at the output stage of the amplifier, the clamp potential is always optimal even if the power supply voltage of the amplifier, the operating environment temperature or the device characteristics vary. Is determined. Therefore, an effective output dynamic range can be obtained. Therefore, it is possible to obtain a sufficiently large gain and an output signal having a sufficiently large amplitude.

The amplifier includes first and second bipolar transistors differentially connected to each other, and the first and second bipolar transistors.
And an emitter resistor connected between the emitters of the second bipolar transistor, a first output buffer connected to the collector of the first bipolar transistor, and a second output buffer connected to the collector of the second bipolar transistor. An output buffer, and first and second bias resistors connected in series between an output side of the first output buffer and an output side of the second output buffer. A connection point between a bias resistor and the second bias resistor may be connected to the clamp circuit.

The amplifier includes first and second bipolar transistors differentially connected to each other, and the first and second bipolar transistors.
An emitter resistor connected between the emitters of the second bipolar transistor, a first emitter follower having a third bipolar transistor connected to the collector of the first bipolar transistor, and an emitter resistor connected to the second bipolar transistor. A second emitter follower having a fourth bipolar transistor connected to the collector; first and second emitter followers connected in series between the emitter of the third bipolar transistor and the emitter of the fourth bipolar transistor; Having a bias resistance of
A connection point between the first bias resistor and the second bias resistor may be connected to the clamp circuit.

Further, the amplifier has a first constant current source connected to the emitter of the third bipolar transistor, and a second constant current source connected to the emitter of the fourth bipolar transistor. be able to.

Further, the potential at the connection point between the first bias resistor and the second bias resistor is determined by the collector potential of the first bipolar transistor and the second bias resistor.
May be an intermediate potential with respect to the collector potential of the bipolar transistor.

Further, the base of the first bipolar transistor may be connected to the clamp circuit, and the base of the second bipolar transistor may be held at a constant potential.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive experiments and research conducted by the present inventors to solve the above problems, the clamp potential is determined in relation to the output potential at the output stage of the amplifier, and the clamp potential is appropriately optimized. Power supply voltage,
It has been found that a sufficiently large output dynamic range can be obtained even when the operating environment temperature and device characteristics vary. On the other hand, in the conventional amplifier circuit shown in FIG. 4, a clamp potential 37 for holding (clamping) an output signal is used.
Is determined by the constant voltage source 35, the output signal of the amplifier circuit is clamped at a constant potential and output. For this reason, even when the operating environment temperature or the like fluctuates, the clamp potential 37 is constant and a sufficiently large output dynamic range cannot be obtained.

Hereinafter, an amplifier circuit according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a block diagram showing an amplifier circuit according to an embodiment of the present invention.

In this embodiment, a capacitor 2 is connected to an input terminal 1 and a clamp circuit 4 is connected to the capacitor 2.
Is connected. Further, an amplifier 6 to which a signal output from the clamp circuit 4 is input is connected to the clamp circuit 4. The output terminal 3 is connected to the amplifier 6.
The signal output from the amplifier 6 is output to the output terminal 3 and is fed back to the clamp circuit 4 as a feedback signal 9. That is, the clamp circuit 4 and the amplifier 6 constitute a feedback clamp circuit. The amplifier 6
The potential 10 determined in association with the output potential at the output stage is the clamp potential of the clamp circuit 4. Further, a constant voltage source 5 is connected to the amplifier 6, and the constant voltage source 5
, The reference potential 8 of the amplifier 6 is determined.

In this embodiment configured as described above, the reference voltage 8 of the amplifier 6 is determined by the constant voltage source 5. Further, the clamp circuit 4 converts the signal input thereto into an amplifier 6.
(Hold) at potential 10 determined by the output stage of
And output. The amplifier 6 amplifies the signal output from the clamp circuit 4 and outputs the amplified signal to the output terminal 3 as an output signal. At this time, the amplifier 6 feeds back a part of the output signal to the clamp circuit 4 as a feedback signal 9. Thus, the amplifier circuit of the present embodiment outputs the output signal clamped at the predetermined potential from the output terminal 3.

Although the output dynamic range of the amplifier circuit fluctuates depending on the power supply voltage, operating environment temperature, variations in element characteristics, and the like, in this embodiment, the clamp potential of the clamp circuit 4 Since it is determined in association with the output potential in the stage, it is possible to optimize the aforementioned fluctuation characteristics. Therefore, even when the output range of the amplifier 6 is deteriorated, a larger effective output dynamic range can be obtained.

Next, the amplifier 6 constituting the amplifier circuit according to the present embodiment will be described more specifically. FIG. 2 is a circuit diagram showing a first specific example of the amplifier constituting the embodiment of the present invention.

In the first specific example of the amplifier 6, a transistor 15 is connected to a terminal 11 connected to the clamp circuit 4.
And 16, the emitter resistor 17, the collector resistors 18 and 1
9, constant current sources 12 and 13, constant voltage source 14, and power supply V
_A differential amplifier circuit composed of _CC is connected. Voltage followers (buffer amplifiers) 20 and 21 are connected to the output terminals of the differential amplifier circuit. Bias resistors 22 and 23 are connected in series between the output terminal of the voltage follower 20 and the output terminal of the voltage follower 21, and the connection point between the bias resistor 22 and the bias resistor 23 is connected to the clamp circuit 4. The terminal 24 to be connected is connected. Thus, the amplifier 6 is configured.

In the amplifier 6 thus configured, the voltage followers 20 and 21 function as output buffers (buffer amplifiers), and the collector potential of the transistor 15 determined by the bias resistors 22 and 23 and the transistor 16 Is output to the terminal 24. Therefore, the clamp circuit 4
Is the intermediate potential of the output dynamic range of the amplifier circuit. Therefore, a large effective output dynamic range can always be obtained even when the operating environment temperature or the like fluctuates.

Next, a second specific example of the amplifier 6 will be described. FIG. 3 shows the second embodiment of the amplifier constituting the embodiment of the present invention.
FIG. 3 is a circuit diagram showing a specific example of the embodiment. In the second specific example shown in FIG. 3, the same components as those in the first specific example shown in FIG.

In the second specific example, a differential amplifier circuit is provided as in the first specific example. The NPN transistors 25 and 26 are connected to the output terminals of the differential amplifier circuit.
The base is connected. Transistors 25 and 26
Are connected to a power supply _Vcc , and the emitters are connected to constant current sources 27 and 28, respectively. Thus, the transistor 25 or 26 forms an emitter follower. Further, bias resistors 22 and 23 are connected between the emitter of the transistor 25 and the emitter of the transistor 26, and a clamp is provided at the connection point between the bias resistors 22 and 23 as in the first specific example. A terminal 24 connected to the circuit 4 is connected. Thus, the amplifier 6 is configured.

In the amplifier 6 configured as described above, a potential intermediate between the collector potential of the transistor 15 and the collector potential of the transistor 16 determined by the bias resistors 22 and 23 is output to the terminal 24. . Therefore, the clamp potential of the clamp circuit 4 becomes an intermediate potential of the output dynamic range of the amplifier circuit.
Therefore, a large effective output dynamic range can always be obtained even when the operating environment temperature or the like fluctuates.

[0025]

As described in detail above, according to the present invention,
The clamp potential is optimized even if the power supply voltage, operating environment temperature, element characteristics, etc. of the amplifier vary, so that a large effective output dynamic range can be obtained. Therefore, an output signal having a sufficiently large gain and a sufficiently large amplitude can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an amplifier circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a first specific example of an amplifier constituting an embodiment of the present invention.

FIG. 3 is a circuit diagram showing a second specific example of the amplifier constituting the embodiment of the present invention.

FIG. 4 is a block diagram showing a conventional amplifier circuit.

[Explanation of symbols]

 1, 3, 11, 24, 31, 33; terminals 2, 32; capacitors 4, 34; clamp circuits 5, 14, 35; constant-voltage sources 6, 36; amplifiers 8, 10, 37, 38; A feedback signal 12, 13, 27, 28; a constant current source 15, 16, 25, 26; a transistor 17, 18, 19, 22, 23; a resistor 20, 21, a voltage follower.

Claims (6)

[Claims] A clamp circuit that holds an input signal at a clamp potential and outputs the signal, and an amplifier that amplifies a signal output from the clamp circuit and outputs the amplified signal while feeding back the signal to the clamp circuit. An amplifier circuit, wherein a clamp potential is determined in association with an output potential at an output stage of the amplifier. 2. The amplifier according to claim 1, wherein the first and second bipolar transistors are differentially connected to each other, an emitter resistor is connected between emitters of the first and second bipolar transistors, and the first and second bipolar transistors are connected to each other. A first output buffer connected to the collector of the bipolar transistor, a second output buffer connected to the collector of the second bipolar transistor, an output side of the first output buffer, and the second output buffer And a first and a second bias resistor connected in series between the first and second output terminals.
2. The amplifier circuit according to claim 1, wherein a connection point between the first bias resistor and the second bias resistor is connected to the clamp circuit. 3. 3. The amplifier includes first and second bipolar transistors that are differentially connected to each other, an emitter resistor connected between emitters of the first and second bipolar transistors, and the first and second bipolar transistors. A first emitter follower having a third bipolar transistor connected to the collector of the bipolar transistor; a second emitter follower having a fourth bipolar transistor connected to the collector of the second bipolar transistor;
First and second bias resistors connected in series between the emitter of the third bipolar transistor and the emitter of the fourth bipolar transistor, wherein the first bias resistor and the second bias resistor are connected in series. The amplifier circuit according to claim 1, wherein a connection point with a bias resistor is connected to the clamp circuit. 4. The amplifier comprises: a first constant current source connected to an emitter of the third bipolar transistor;
4. The amplifier circuit according to claim 3, further comprising: a second constant current source connected to an emitter of the fourth bipolar transistor. 5. A potential at a connection point between the first bias resistor and the second bias resistor is an intermediate potential between a collector potential of the first bipolar transistor and a collector potential of the second bipolar transistor. The amplifier circuit according to claim 2, wherein: 6. The device according to claim 2, wherein a base of the first bipolar transistor is connected to the clamp circuit, and a base of the second bipolar transistor is held at a constant potential. 2. The amplifier circuit according to claim 1.