JPH01149603A - Negative feedback amplifier circuit - Google Patents

Abstract

PURPOSE:To realize a band compensating characteristic against a wide band by connecting drains of two FETs in parallel with each other and impressing input signals upon the gate of one of the two FETs and feedback signals upon the gate of the other FET and, at the same time, connecting band compensating circuits respectively composed of a resistance and capacity and inductance and resistance to the gates of the FETs. CONSTITUTION:FETs 31 and 32 are connected in parallel with each other and input signals and feedback signals are respectively inputted to the gates of the FETs 31 and 32. Therefore, an input signal path and feedback path can be separated from each other and input impedance and feedback quantities can be set independently to desired values. The input impedance value is nearly decided by a resistance 53, since the input impedance of an FET is usually extremely high. Moreover, two band compensating circuits and an impedance matching circuit are provided. As a result, the band compensating capacity of each band compensating circuit is reduced and the compensating range of each circuit can be changed. Accordingly, the circuit can be designed easily and the compensating band can be set at a higher level.

Description

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

[Conventional technology]

FIG. 4 is a circuit diagram showing a conventional negative feedback amplifier circuit.

Figure 4 shows a gallium arsenide (hereinafter referred to as GaAs) FE as a field effect transistor (hereinafter referred to as FET).
This figure shows the configuration of a source-grounded-stage AC-coupled negative feedback amplifier circuit using T.

For this example, see Volume 17, No. 10 of MAICROWAVES, October 1978.
The paper in the issue, “Use Negative Feedback,
Toe Slash Wideband Buinis Double R J (UseNegative Feedback
kT.

5lash Wideband VSWR, MIC
ROWAVES OCT 1978. Vol17N
o, 10). G used in this circuit
aAs-FET has characteristics 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 a microwave band oscillation circuit. It is widely used. In addition, since the electron mobility is high, the mutual conductance gm is also large, and the series resistance and parasitic capacitance are small, so there are advantages 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 gate potential of the FET 3 is set by the resistor 5.
A DC power supply VOG is applied from a terminal 58 through a bias circuit constituted by a resistor 53 and a resistor 53 . If there is no feedback resistor 54, the signal input to FET3 is
The voltage is amplified by a voltage amplification value determined by the product of the mutual conductance gm of No. 3 and the resistance value of the load resistor 56, and is output from the output end 2 via a DC cutoff capacitor 57 provided on the output side. In general, applying negative feedback to amplifier circuits is widely used for the purpose of improving stability against power supply fluctuations, absorbing characteristic fluctuations due to transistor variations, improving nonlinear distortion, and further widening the band. As shown in FIG. 4, a circuit type is known in which a feedback resistor 54 is inserted to provide a feedback path for controlling the voltage period from the drain to the gate of the FET 3. The capacitor 55 is for blocking the direct current component of the return path. The feedback amount 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.

[Problem that the invention seeks to solve]

In the conventional feedback amplifier circuit described above, it is difficult to widen the band 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 input impedance of the feedback amplifier circuit is Since it is impossible to set the input impedance and the amount of feedback independently, it takes time and effort to design the circuit, and the range in which the input impedance and the amount of feedback can be set is severely restricted. 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, in order to improve this point, an equalization circuit consisting of C and R was inserted in connection with the amplifier circuit shown in Fig. 4.
They took measures to further amplify it. However, this method has drawbacks such as deterioration of characteristics due to multi-stage connection of amplifier circuits and an increase in the number of amplification stages. Another method is to insert an inductance 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 value of inductance is increased in order to ensure good characteristics, stray capacitance increases, which in turn causes a decrease in the self-resonant frequency, making it impossible to obtain good characteristics. There is. Also, GB/S band (~
When considering the realization of a wideband amplifier up to 10GH2),
The (S21) characteristics of the transistor are approximately 6DB10C.
Since the frequency decreases with T, it is impossible to secure a sufficient bandwidth with a simple C-R coupled amplifier. Furthermore, even if negative feedback is applied, the band will be widened but the gain will be reduced. Furthermore, even if a peaking circuit is used, it only works to raise the upper limit band, so it has many drawbacks, such as making it difficult to significantly extend the band to the high frequency side.

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. Another object of the present invention is to provide a negative feedback amplifier circuit that has two band compensation circuits and divides the band compensation characteristics to realize band compensation for a high band, and has a wide frequency characteristic.

A second object of the present invention is to eliminate the above-mentioned drawbacks and to
It is an object of the present invention to provide a negative feedback amplifier circuit which can be used in a wide band and whose gain can be varied by varying the gate voltage of a field effect transistor to which a feedback signal is applied without changing the resistor voltage division ratio that determines the amount of feedback.

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.

[Means for solving problems]

The negative feedback amplifier circuit of the first invention includes a first band compensation circuit formed by connecting a first resistor and a capacitor in parallel, a second band compensation circuit formed by series connection of a second resistor and an inductance, and an input A low-pass microwave band impedance matching/conversion circuit configured to receive a signal and comprising a distributed constant line and a third resistor, and a gate at the output end of the low-pass microwave band impedance matching/conversion circuit. connected to input the output signal of the low-pass type microwave band impedance matching/conversion circuit; the drain is connected to the power supply terminal via the second band compensation circuit; and the source is connected to the power supply terminal via the first band compensation circuit. a second field effect transistor whose drain is connected to the train of the first field effect transistor and whose source is grounded; and a feedback circuit connected between the gates of the second field effect transistor.

Further, the negative feedback amplifier circuit of the second invention includes a first band compensation circuit by connecting a first resistor and a capacitor in parallel, a second band compensation circuit by connecting a second resistor and an inductance in series, A low-pass microwave band impedance matching/conversion circuit that receives an input signal and is composed of a distributed constant line and a third resistor, and a gate at the output end of the low-pass microwave band impedance matching/conversion circuit. is connected to the low-pass microwave band impedance matching/
a first field effect transistor, which receives the output signal of the conversion circuit, has a drain connected to a power supply terminal via the second band compensation circuit, and has a source grounded via the first band compensation circuit; a second field effect transistor connected to the train of the first field effect transistor and having a grounded source; 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; and a feedback circuit having a variable DC power supply that changes the gate potential of the second field effect transistor.

Furthermore, the negative feedback circuit of the third invention includes a first band compensation circuit formed by connecting a first resistor and a capacitor in parallel, a second band compensation circuit formed by series connection of a second resistor and an inductance, and an input A low-pass microwave band impedance matching/conversion circuit configured to receive a signal and comprising a distributed constant line and a third resistor, and a gate at the output end of the low-pass microwave band impedance matching/conversion circuit. The output signal of the low-pass microwave band impedance matching/conversion circuit is connected to the power supply terminal via the second band compensation circuit, and the source is connected to the power supply terminal via the first band compensation circuit. a first field effect transistor whose drain is connected to the train of the first field effect transistor and whose source is grounded; and a drain input of the first field effect transistor. and a feedback circuit having a variable resistor connected between the gates of the second field effect transistor and changing the amount of signal input to the gate of the second field effect transistor.

〔Example〕

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

FIG. 1 is a circuit diagram showing an embodiment of the first invention. The embodiment of FIG. 1 includes first and second field effect transistors FET31. The drains of the FETs 32 are connected in parallel, and the gate of the FET 31 is connected to a capacitor 51.
An input signal is applied via a low-pass microwave band impedance matching/conversion circuit 5o, a part of the output signal is applied to the gate of FET 32 via a feedback circuit 10, and the source of FET 31 is connected to a capacitor. A band compensation circuit 1000 as a first band compensation circuit consisting of a parallel connection of a resistor 101 and a resistor 102 as a first resistor is removed and grounded, and the drains and voltages of FET31 and FET32 connected in parallel are connected to the ground. (2) A terminal 1001 connected to the oD DC power supply is provided and serves as a load for FET31 and FET32. In Figure 1, FET
A DC bias of 31.32 is applied from terminal 59 via resistor 56 and inductance 103. 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. Capacitors 51, 57, and 55 are all DC-blocking capacitors. In the figure, as an example of the configuration of the feedback circuit 10, an example using AC coupling is shown. The input signal input to the input terminal 1 has its DC component cut off by the capacitor 51 and is input to the gate of the FET 31 . The low-pass microwave band impedance matching circuit 511 in the low-pass microwave band impedance matching/conversion circuit 50 is a lossless matching circuit, and the impedance looking toward the signal source side at the upper limit of the band is complex in any cut plane. The conditions are set such that there is a conjugate relationship and the power reflection coefficient [S]2 becomes zero. The resistor 53 determines the input impedance, but in the microwave band, it is converted to a high impedance by a low-pass microwave band impedance conversion circuit 531 and has almost no effect on the main line. Therefore, impedance matching by the lossless circuit is sufficiently performed, and the maximum available power gain of the FET 31 can be changed at the upper limit of the band. The DC gate potential of the FET 31 is given by a bias circuit composed of a resistor 52 connected via a terminal 58 to a DC power source 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 capacitor 101 and resistor 102 of the band compensation circuit 1000 and the inductance 1 of the band compensation circuit 1001.
It has a peaking characteristic determined by 03 and resistance 56,
This results in improved broadband characteristics. Inductance 103, resistance 56, capacitor 1
01, and the value of the resistor 102 can be appropriately selected according to desired characteristics. On the other hand, a part of the output signal is input to the gate 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 R9 of the feedback resistor 54. In addition, in the case of the circuit configuration shown in Fig. 1, the FET
31 and FET 32 are connected in parallel, so the FE
The load resistance value of T31 is determined by the resistor 56, the input resistance of the feedback circuit 10, the mutual conductance gm of FET31, and the FET3
It is determined by the relationship with the load resistance value of 1.

The circuit shown in FIG.
The configuration is such that a feedback signal is input to each of the 32 gates. 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, which facilitates circuit design. In this case, the value of the input impedance is determined by the resistor 53 since the input impedance of the FET is usually very high. Furthermore, since the circuit shown in FIG. 1 has two band compensation circuits and an impedance matching circuit, the band compensation capability of each circuit is reduced.
In addition, the scope of compensation can be changed and configured.
The compensation band can also be set high.

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

FIG. 2 is a circuit diagram showing an embodiment of the second invention. In the embodiment shown in FIG. 2, the drains of FETs 31 and 32 are connected in parallel, and the gate of FET 31 is connected to a capacitor 51.
An input signal is applied through a low-pass microwave band impedance matching/conversion circuit 50, and a part of the output signal is applied to the gate of the FET 32 through a feedback resistor 54, and a voltage is applied as a gate bias DC voltage of the FET 32. v
A cori'r variable DC voltage source 13 is provided, and an FET
The source of FET 31.
A band compensation circuit 1001 consisting of an inductance 103, a resistor 56, and a series circuit is provided between the drain of the FET 32 and the DC power supply 59 of the voltage DD.
It is configured as two loads.

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 have a peaking characteristic determined by the band compensation circuits 1000 and 1001 and a broadband characteristic whose band is improved by the low-pass type microwave band impedance matching/conversion circuit 50.

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 FET32 is the voltage VCON
The output voltage of variable DC power supply 13 of T is set by resistor 11 and resistor 1.
It is the value obtained by dividing the pressure by 2. In addition, in the circuit of Fig. 2, F
Since ET31 and FET32 are connected in parallel,
The load resistance value of the FET 31 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 the FET
The DC operating point of FET 32 changes and therefore the transconductance of FET 32 changes. Therefore, the voltage transfer function of the negative feedback circuit, in other words, the amount of feedback can be changed. That is, by using the variable DC power supply 13, 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 cause parasitic impedance, so it has the feature that the gain can be varied 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 wider-band negative feedback amplifier circuit capable of Another feature is that circuit design is easy.

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

FIG. 3 is a circuit diagram showing an embodiment of the third invention. The embodiment shown in FIG. 3 includes FET 31. The drain of FET32 is connected, and the gate of FET31 is connected to a capacitor 51.
An input signal is applied through a low-pass microwave band impedance matching/conversion circuit 50, a part of the output signal is applied to the gate of the FET 32 through a variable feedback circuit 30, and a band compensation circuit 1000 is applied. , band compensation circuit 1
001 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 to 2 is transmitted through the variable resistor 541 of the variable feedback circuit 30.
applied via. The amount of feedback at this time is applied via the variable resistor 541 of the variable feedback circuit 30. The feedback amount at this time is the resistance value Rfv 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 changes, and the gain of the amplifier circuit can be made variable. The DC gate potential of FET32 is resistor 11 and resistor 12.
Therefore, even if the variable resistor 541 is changed, the DC gate potential of the FET 32 is kept constant. Third
In the circuit shown in the figure, band compensation circuits 1000, 1001, . The low-pass microwave band impedance matching/conversion circuit 50 provides a wider frequency characteristic. Further, the input signal path and the feedback path can be separated, and a wideband negative feedback amplifier circuit can be obtained in which the input impedance and the amount of feedback can be set independently. Furthermore, by using the circuit shown in FIG. 3, it is possible to construct a so-called AGC circuit that changes the gain in response to fluctuations in the input level and always obtains a constant output signal level.

In the above explanation, a case has been described in which a GaAs-FET is used as a FET suitable for configuring a wideband amplifier circuit, but the scope of the present invention is not limited to this, and it can also be applied to a case where a silicon FET is used. Needless to say, the same applies.

〔Effect of the invention〕

As explained above, according to the first invention, two FET trains are connected in parallel as a broadband amplifier circuit using FETs, and a low-pass microwave band impedance matching is provided at the gate of one FET. /The input signal is applied through the conversion circuit, the feedback signal is applied to the gate of the other FET, and a band compensation circuit consisting of a resistor and capacitor is connected between the source of the FET to which the input signal is applied and the ground. Furthermore, by connecting and using a band compensation circuit consisting of an inductance and a resistance between the connected drains of the two FETs and the DC voltage source, the input impedance and feedback amount can be set independently. This has the advantage that it is possible to realize a band compensation characteristic for a wide band, and to obtain a negative feedback amplifier circuit that has a wide band characteristic and has good stability.

Further, according to the second invention, by changing the DC gate bias voltage of the FET to which the feedback signal is applied in the circuit of the first invention using a variable DC voltage source, the gain is variable and the input impedance and the amount of feedback can be adjusted. This has the effect of being able to be set independently and replacing the negative feedback amplifier circuit with good frequency characteristics.

Furthermore, according to the third invention, by using a variable resistor as 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 set independently and stabilized. This has the effect of providing a negative feedback amplifier circuit with excellent frequency characteristics.

[Brief explanation of the drawing]

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. 4 is a circuit diagram showing a conventional negative feedback amplifier circuit. 1... Input end, 2... Output end, 13... Variable DC power supply, 3, 31. 32... FET, 52, 53, 11
．． 12,56,102...Resistor, 54...Feedback resistor, 541...Variable resistor, 51.57,55,101...
... Kendansa, 103 ... Inductance, 100
0...First band compensation circuit, 1001...Second band compensation circuit, 50...Low pass type microwave band impedance matching/conversion circuit, 511...Low pass type microwave band Impedance matching circuit, 531...Low-pass type microwave band impedance conversion circuit. Agent Patent Attorney Uchihara Otoyo 1 Kuchi 2 Tsukasa 3rd Inquiry 4

Claims (3)

[Claims] (1) A first band compensation circuit by connecting a first resistor and a capacitor in parallel, a second band compensation circuit by connecting a second resistor and an inductance in series, and a distributed constant line to which an input signal is input. A gate is connected to the output terminal of a low-pass type microwave band impedance matching/conversion circuit composed of a third resistor, and an output signal of the low-pass type microwave band impedance matching/conversion circuit is inputted to the drain. a first field effect transistor connected to a power supply terminal via the second band compensation circuit, a source of which is grounded via the first band compensation circuit; and a train connected to the drain of the first field effect transistor. a second field effect transistor whose source is grounded; and a feedback circuit connected between the drain of the first field effect transistor and the gate of the second field effect transistor, A negative feedback amplifier circuit, characterized in that a band-compensated and amplified output signal is obtained from the drain of the first field effect transistor. (2) A first band compensation circuit by connecting a first resistor and a capacitor in parallel, a second band compensation circuit by connecting a second resistor and an inductance in series, and a distributed constant line to which an input signal is input. a low-pass type microwave band impedance matching/conversion circuit comprising a third resistor, and a gate connected to the output end of the low-pass type microwave band impedance matching/conversion circuit, A first electric field is connected to the output signal of the waveband impedance matching/conversion circuit, the drain is connected to the power supply terminal via the second band compensation circuit, and the source is grounded via the first band compensation circuit. a second field effect transistor having a drain connected to the drain of the first field effect transistor and a source grounded; a drain of the first field effect transistor and a gate of the second field effect transistor; and a feedback circuit having a variable DC power supply connected between the drain and the drain of the first field-effect transistor to change the gate potential of the second field-effect transistor. A negative feedback amplifier circuit characterized in that it obtains from (3) A first band compensation circuit by connecting a first resistor and a capacitor in parallel, a second band compensation circuit by connecting a second resistor and an inductance in series, and a distributed constant line to which an input signal is input. a low-pass type microwave band impedance matching/conversion circuit comprising a third resistor, and a gate connected to the output end of the low-pass type microwave band impedance matching/conversion circuit, The output signal of the waveband impedance matching/conversion circuit is inputted, the drain is connected to the power supply terminal through the second band compensation circuit, and the source is connected to the first electric field grounded through the first band compensation circuit. an amount of signal input to the gate of the second field effect transistor connected between the effect transistor and the gate of the second field effect transistor whose drain is connected to the drain of the first field effect transistor and whose source is grounded. a feedback circuit having a variable resistance to be changed, and an output signal obtained by band-compensating and amplifying the input signal is obtained from the drain of the first field effect transistor.