JPS62136114A - Negative feedback amplifier circuit - Google Patents

Abstract

PURPOSE:To set independently an input impedance and a feedback quantity and to realize a broad band characteristic by providing two FETs whose drains are connected in parallel, inpressing an input signal to one gate, inpressing a feedback signal to the other gate and providing the 1st and 2nd band compensation circuits. CONSTITUTION:A DC bias of the FETs 31, 32 whose drains are connected in parallel is fed from a terminal 59 having a voltage VDD via a band compensation circuit 1001. A resistor 56 and an inductance 103 of the circuit 1001 constitute a series peaking circuit. The input signal is inputted to a gate of the FET 31 and the DC gate potential is given by a bias circuit comprising resistors 52, 53 connected to a voltage VGG. The frequency characteristic of a signal outputted while being amplified by the FET 31 has a peaking characteristic depending on the inductance 103 and the resistance 56 of the circuit 1001 and a capacitor 101 and a resistor 102 of a band compensation circuit 1000 so as to attain a wide band characteristic. Since the input signal is given to the gate of the FET 31 and a feedback signal is inputted to the gate of the FET 32 as the constitution, the input impedance and the feedback quantity are set independently to facilitate the circuit design.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a negative feedback amplifier circuit.

[Conventional technology]

FIG. 11 shows a conventional negative feedback amplifier circuit.

The figure shows an example of the configuration of a single-stage AC-coupled negative feedback amplifier circuit using a gallium arsenide (hereinafter referred to as GaAs) FET as a field effect transistor (hereinafter referred to as FET). It is. For this example, see Microwaves (MI) published in October 1978.
CROWAVE), Vol. 17, No. 10, the paper ``Use I Gotta Feedback Totsu Slash Wideband VS Double You'' (
Use Negative Feedback
o S 1 a s h W i cl e b
a n d V S XV R.

MICROWAVES OCT 1978. V.

)'17 No. 10). The GaAs-FET used in this circuit has features such as a very high maximum oscillation frequency, large maximum available power gain, and low noise compared to silicon bipolar transistors, so it can be used as a wideband low-noise amplifier or Widely used in microwave band oscillation circuits, etc. In addition, since the mobility of electrons is high, the mutual conductance gm also increases1,
Due to the small series resistance and small parasitic capacitance, it has the advantage of high speed operation and low power consumption. In FIG. 4, the DC component of the signal input to the input terminal 1 is blocked by the capacitor 51, and the signal is input to the gate of the FET 3. The gate potential of the FET 3 is applied from a terminal 58 to a DC power supply VGG via a bias circuit constituted by a resistor 52 and a resistor 53. Feedback resistor 54
If there is no signal, the signal input to the FET 3 is amplified by the voltage amplification variation determined by the product of the mutual conductance g111 of the FET 3 and the resistance value of the load resistor 56, and the signal is amplified by the voltage amplification variation determined by the product of the mutual conductance g111 of the FET 3 and the resistance value of the load resistor 56, and then the signal is amplified by the voltage amplification variation determined by the product of the mutual conductance g111 of the FET 3 and the resistance value of the load resistor 56. It is output from the output end 2. In general, improved stability against power fluctuations,
Applying negative feedback to amplifier circuits is widely used for the purpose of absorbing characteristic fluctuations due to transistor variations, improving nonlinear distortion, and achieving even wider bandwidth.An example of this is shown in Figure 4. A circuit type in which a resistor 54 is inserted to provide a feedback path for voltage feedback from the drain to the gate of the FET 3 is known. The capacitor 55 is for blocking the direct current component of the return path. The amount of return is
It is approximately determined by the voltage division ratio between the impedance value of the resistor 52, the resistor 53, and the output impedance of the input signal source in parallel, and the resistance value of the feedback resistor 54.

However, in such conventional feedback amplifier circuits, it is difficult to increase the bandwidth beyond a certain level due to the capacitance of the field effect transistor itself, and furthermore, since the feedback path is connected to the input signal path, the feedback Since it is impossible to set the input impedance and feedback amount of the amplifier circuit independently, it takes time and effort to design the circuit, and there are considerable restrictions on the range in which the input impedance and feedback amount can be set. Ta. Furthermore, when using a negative feedback amplifier circuit as shown in Fig. 4 as a front-end amplifier of a high-speed optical receiver circuit, the band characteristics of the output signal of the amplifier circuit deteriorate due to the time constant of the photodetector capacitance and load resistance. It has become a characteristic. Conventionally, to improve this point, the fourth
In addition to the amplifier circuit shown in the figure, a circuit consisting of C and R was inserted into the b-C group to further increase and expand the circuit. However, this method has drawbacks such as poor characteristics due to the multistage connection of amplifier circuits and an increase in the number of amplification stages. In addition, as a means for compensating for bandwidth compensation, an inductance is inserted between the load resistor 56 of the amplifier circuit shown in FIG. There is a way to do this. However, even with this method, if the inductance value is increased in order to ensure good characteristics, the stray capacitance will increase, and the self-resonant frequency will decrease, making it impossible to obtain good characteristics. had.

[Purpose of the invention]

A first object of the invention is to eliminate the above-mentioned drawbacks and to provide a negative feedback amplifier circuit that can independently set the input impedance and the amount of feedback, has a wide band, and is easy to design. In addition, it is equipped with two band compensation circuits and divides the band compensation characteristics to achieve band compensation for high bands.
The purpose of the present invention is to provide a negative feedback amplifier circuit 3 having a wide frequency characteristic.

A further object of the present invention is to eliminate the above-mentioned drawbacks and to provide feedback (2
An object of the present invention is to provide a negative feedback amplifier circuit which can be used in a wide band and whose gain can be varied by making the voltage of a field effect transistor to which a signal is applied variable.

A third object of the present invention is to provide a negative feedback amplifier circuit which eliminates the above-mentioned drawbacks and allows a wide band and variable gain by making a part of the feedback path variable gain.

[Structure of the invention]

According to the present invention, a first band compensating circuit is formed by connecting a first resistor and a capacitor in parallel, a second band compensating circuit is formed by connecting a second resistor and an inductance in series, and an input signal is input to the gate. a first field effect transistor to which a signal is input, whose drain is connected to the power supply terminal via the second band compensation circuit, and whose source is grounded via the first band compensation circuit; a second field effect transistor connected to the drain of the field effect transistor and having its source grounded; and a feedback circuit connected between the drain of the first field effect transistor and the gates of the second field effect transistors. There is obtained a negative feedback amplifier circuit, characterized in that an output signal obtained by band-compensating and amplifying the input signal is obtained from the drain of the first field effect transistor.

Furthermore, according to the present invention, the first band compensation circuit is configured by connecting a first resistor and a capacitor in parallel, the second band compensation circuit is configured by connecting a second resistor and an inductance in series, and an input signal is input to the gate. a first field effect transistor to which a signal is input, whose drain is connected to the power supply terminal via the second band compensation circuit, and whose source is grounded via the first band compensation circuit; a second field effect transistor connected to the drain of the field effect transistor and having its source grounded; and a transistor connected between the drain of the first field effect transistor and the second field effect transistor transistor; a feedback circuit having a variable DC power supply that changes the potential of the gate of the second field effect transistor, and obtains an output signal obtained by band-compensating and amplifying the input signal from the drain of the first field effect transistor. A negative feedback amplifier circuit characterized by the following is obtained.

Furthermore, according to the present invention, the first band compensation circuit is configured by connecting a first resistor and a capacitor in parallel, the second band compensation circuit is configured by connecting a second resistor and an inductance in series, and an input signal is input to the gate. a first field effect transistor to which a signal is input, whose drain is connected to the power supply terminal via the second band compensation circuit, and whose source is grounded via the first band compensation circuit; a second field effect transistor connected to the drain of the field effect transistor and having its source grounded; and a second field effect transistor connected between the drain of the first field effect transistor and the gate I of the second field effect transistor. a feedback circuit having a variable resistor that changes the amount of signal input to the gate of the first field effect transistor, and a feedback circuit having a variable resistance that changes the amount of signal input to the gate of the first field effect transistor; A negative feedback enhancement circuit is obtained, which is characterized in that it is obtained from the following.

〔Example〕

Hereinafter, the first invention will be described in detail with reference to the drawings.

In FIG. 1, the drains of FET31 and FET32 are connected in parallel, an input signal is applied to the gate of FET31 via a capacitor 51, and FET31 and FET32 are connected in parallel.
E T 3 at the gate of 32? A part of the output signal is applied through the fJ & circuit 10, and further F E
The source of T31 is connected to the ground via a band compensation circuit 1000 consisting of a capacitor 1'01 and a resistor 102 connected in parallel, and an FET connected in parallel.
A band compensation circuit 1001 consisting of a series circuit of an inductance 103 and a resistor 56 is provided between the drains of FET 31 and FET 32 and a terminal 59 connected to a DC power supply of voltage DD. FIG. 3 is a diagram showing an embodiment of the invention. In the same figure, FET: 31
, 32 has a resistor 56 and an intance 103
It is added from five terminals via. The resistor 56 and the inductance 103 constitute a series peaking circuit.

The resistor 56 may be a passive element such as a normal resistor, or may be an active element including a FET. The capacitors 51, 57, and 55 are both DC cutoff capacitors. In the figure, as an example of the configuration of the feedback circuit 10, an example using AC coupling is shown. The input (No. 3) input to input terminal 1 is input to the gate of FET 31 after its DC component is blocked by capacitor 51. FET 31
The DC gate I potential is given by a bias circuit composed of resistors 52 and 53 connected via a terminal 58 to a DC power supply of voltage VGG. The DC component of the signal amplified by the FET 31 and output to the drain is blocked by the capacitor 57, and the signal is output from the output terminal 2. The frequency characteristics of this output signal are determined by the band compensation circuit 100.
It has a peaking characteristic determined by a capacitor 101 of zero, a resistor 102, an inductance 103 of a band compensation circuit 1001, and a resistor 56, and thereby has a wide band characteristic with an improved band. inductance 103
．． Resistance 56. Capacitor 101. It is necessary to appropriately select the value of resistor 102 according to the desired characteristics.

On the other hand, a part of the output signal is input to the gate L- of the FET 32 via the feedback resistor 54 of the feedback circuit 10. The phase of this signal is the inverted phase of the input signal at input terminal 1.

The gate potential of the FET 32 is applied to the terminal 5 via a bias circuit composed of a resistor 11 and a resistor 12 of the feedback circuit 10.
It is supplied from a DC power supply connected to 8. The magnitude of the signal fed back to the FET 32 is approximately determined by the ratio of the resistance value of the resistor 11 and the resistor 12 in parallel to the resistance value R5 of the feedback resistor 54.

In addition, in the case of the circuit configuration shown in Fig. 1, FET31 and FET
32, the load resistance value of FET 31 is determined by the input resistance of feedback circuit 10 and FE
This is what happens when the operating resistance of T32 is connected in parallel. Therefore, the open circuit voltage gain is determined by the relationship between the mutual conductance gm of the FET 31 and the load resistance value of the FET 31.

The circuit shown in FIG.
The configuration is such that a feedback signal is input to each gate of 32. Therefore, the input signal path and the feedback path can be separated, and the input impedance and feedback amount can be independently set to desired values, making circuit design easy. In this case, the value of the input impedance is determined by the parallel value of the resistor 52 and the resistor 53, since the input impedance of the FET is usually very high.

In addition, since the circuit shown in Figure 1 has two band compensation circuits, the band compensation ability of each circuit is reduced, and the compensation range can be changed, so the compensation band is also high. You can take it.

Next, the second invention will be described in detail with reference to the drawings.

In Figure 2, the drains of FET31 and FET32 are connected in parallel, an input signal is applied to the gate of FET31, and FET3
A part of the output signal is applied to the gate of FET 2 via a feedback resistor 54, and a variable DC voltage source 13 of voltage VCONT is provided as a gate bias DC voltage of FET 32, and the source of FET 31 is connected to a capacitor. 101
and a resistor 102 connected in parallel.
000 to the ground, and further connected in parallel with FET31. Drain of FET32 and voltage VD
A band compensation circuit 1001 consisting of a series circuit of an inductance 103 and a resistor 56 is provided between the five DC power supplies of D,
The second load was FET 31 and FET 32.
FIG. 3 is a diagram showing an embodiment of the invention.

The signal input to the input terminal 1 is amplified by the FET 31, the DC component is blocked by the capacitor 57, and the signal is output from the output terminal 2. The frequency characteristics of this output signal are wide-band characteristics that are improved by the peaking characteristics determined by the band compensation circuit 1000 and the band compensation circuit 1001.

A FET is connected to the gate of the FET 32 via a feedback resistor 54.
A part of the output signal of No. 31 is input. The DC gate bias voltage of the FET 32 is a value obtained by dividing the output voltage of the variable DC voltage source 13 of the voltage VCONT by the resistors 11 and 12. Note that in the circuit of FIG. 2, FET31 and FET32 are connected in parallel, so FET31
The load resistance value is obtained by connecting the load resistance 56, the input resistance of the variable feedback circuit 20, and the operating resistance of the FET 32 in parallel.

Now, when the output voltage of the variable DC power supply 13 is changed, the DC gate bias voltage of the FET 32, which is determined by the voltage division ratio between the resistors 11 and 12, changes. This allows FE
The DC operating point of T32 changes and therefore the transconductance of FET 32 changes. Therefore, by using the variable DC voltage source 13 that can change the voltage transfer function of the negative feedback circuit, in other words, the amount of feedback, the gain of the negative feedback amplifier circuit can be made variable.

This variable gain amplifier circuit does not use a variable resistance element that tends to generate parasitic impedance, so it has the advantage of being able to vary the gain without deteriorating the frequency characteristics of the gain even if the gain amount is changed significantly. . According to this embodiment, it is possible to configure a so-called AGC circuit that always obtains a constant output signal level by changing the gain in response to fluctuations in the input signal level, and also sets the input impedance and feedback amount independently. A wideband negative feedback amplifier circuit capable of Another advantage is that circuit design is easy.

Next, the third invention will be explained with reference to the drawings.

FIG. 3 shows FET31. The drain of FET32 is connected, the input signal is applied to the gate of FET31, and FET3
A part of the output signal is applied to the gate of 1000.2 via the variable feedback circuit 30, and a band compensation circuit 1000. FIG. 7 is a diagram showing an embodiment of the third invention in which a band compensation circuit 1001 is provided.

The configuration of FIG. 3 uses a variable resistor 541 in place of the feedback resistor 54 in the circuit of FIG. FET3
The feedback signal of 2/\ is a variable feedback port! 330 variable resistor 5
41. The feedback amount at this time is the resistance value Rrv of the variable resistor 541 and the resistor 11. It is determined by the ratio to the parallel connection value of the resistor 12.

Therefore, by changing the variable resistor 541, the amount of feedback can be changed, and the gain of the amplifier circuit can be made variable.The DC gate potential of the FET 32 is set by the resistors 11 and 12, so it can be made variable. Even if the resistor 541 is changed, the DC gate potential of the FET 32 remains constant at 1. In the circuit shown in Fig. 3, the frequency characteristics are widened by using the Bandura 1 old circuit 1000.1001, as in the circuit shown in Fig. 1. In addition, the input signal path and the feedback path can be separated, and a wideband negative feedback amplification circuit can be obtained in which the input impedance and the amount of feedback can be set independently. By using this circuit, it is possible to construct a so-called AGC circuit that changes the gain in response to fluctuations in the input signal level and always obtains a constant output signal level.

Although the above description has been made regarding the use of JAsFET as a PET suitable for constructing a wideband amplifier circuit, the scope of the present invention is not limited to this, and silicon Needless to say, the same applies when FETs are used.

〔Effect of the invention〕

As explained above, according to the first invention, as a broadband amplifier circuit using FETs, the drains of two FETs are connected in parallel, an input signal is applied to the gate h of one FET, and A feedback (No. 8) is applied to the gate of the FET, and a band compensation circuit (100
0), and by connecting and using a band compensation circuit (1001) consisting of an inductance and a resistance between the connected drains of the two FE and T and the DC voltage source, the input impedance and feedback can be adjusted. A broadband negative feedback amplifier circuit with good stability and wideband characteristics can be obtained.

Furthermore, according to the second invention, in the circuit of the first invention,
By varying the DC bias voltage of the FET to which the feedback signal is applied using a variable DC voltage source, the gain is variable, the large current conductance and the 4m feedback can be set independently, and the frequency characteristics are A wideband negative feedback amplifier circuit with good performance can be obtained.

Furthermore, according to the third invention, by using a variable resistor at 1° with the feedback resistor in the feedback path of the broadband negative feedback amplifier circuit in the first invention, the gain is variable and the input impedance and feedback amount can be adjusted. A wideband negative feedback amplifier circuit that can be set independently and has good stability and excellent frequency characteristics can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the first invention, FIG. 2 is a circuit diagram showing an embodiment of the second invention, and FIG. 3 is a diagram showing an embodiment of the third invention. FIG. 11 is a circuit diagram showing a conventional wideband negative feedback amplifier circuit. 3.31.32...FET, 52, 53, 11°12
．． 56.102...Resistance, 54...Feedback resistance, 54
1... Variable resistance, 51.57, 55, 101... Capacitor, 103... Inductance, 1000.
...First band compensation circuit, 1001...Second band compensation circuit, 1...Input end, 2...Output end, 13...
Variable DC power supply. [-/ Meat 1 figure Haya 3 figure

Claims (1)

[Claims] 1. A first band compensation circuit formed by a parallel connection of a first resistor and a capacitor, a second band compensation circuit formed by a series connection of a second resistance and an inductance, and a gate a first field effect transistor to which an input signal is input, a drain connected to a power supply terminal via the second band compensation circuit, and a source grounded via the first band compensation circuit;
a second field effect transistor whose drain is connected to the drain of the first field effect transistor and whose source is grounded; and a second field effect transistor connected between the drain of the first field effect transistor and the gate of the second field effect transistor. 1. A negative feedback amplification circuit, comprising: a feedback circuit that performs band compensation on the input signal and amplifies the output signal from the drain of the first field effect transistor. 2. A first band compensation circuit with a parallel connection of a first resistor and a capacitor, a second band compensation circuit with a series connection of a second resistor and an inductance, and a drain with an input signal input to the gate. a first field effect transistor connected to a power supply terminal via the second band compensation circuit and whose source is grounded via the first band compensation circuit;
a second field effect transistor whose drain is connected to the drain of the first field effect transistor and whose source is grounded; and a second field effect transistor connected between the drain of the first field effect transistor and the gate of the second field effect transistor. a feedback circuit having a variable DC power supply that changes the potential of the gate of the second field effect transistor, and an output signal obtained by band-compensating and amplifying the input signal from the drain of the first field effect transistor. A negative feedback amplifier circuit characterized in that the negative feedback amplifier circuit has the following characteristics: 3. A first band compensation circuit with a first resistor and a capacitor connected in parallel, a second band compensation circuit with a series connection of a second resistor and an inductance, and a gate with an input signal input to the drain. a first field effect transistor connected to a power supply terminal via the second band compensation circuit and whose source is grounded via the first band compensation circuit;
a second field effect transistor whose drain is connected to the drain of the first field effect transistor and whose source is grounded; and a second field effect transistor connected between the drain of the first field effect transistor and the gate of the second field effect transistor. a feedback circuit having a variable resistor that changes the amount of a signal input to the gate of the second field effect transistor; A negative feedback amplifier circuit characterized in that the feedback is obtained from the drain.