JPH0624296B2 - Negative feedback amplifier circuit - Google Patents

Description

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.
FIG. 4 shows gallium arsenide (hereinafter abbreviated as GaAs) F as a field effect transistor (hereinafter abbreviated as FET) F
1 shows a configuration of a source grounded one-stage AC coupled negative feedback amplifier circuit using ET.

Regarding this example, Vol. 17, No. 17 of Microwaves, published in October 1978.
The article in the issue "Use negative feedback
To Slash Wideband Biese Double Earl "(Use Negative Feedback
To Flash Wideband VSWR. MI
CROWAVES OCT 1978, Vol17N
o. 10). G used in this circuit
The aAs-FET has a characteristic that the maximum oscillation frequency is much higher than that of the silicon bipolar transistor, the maximum available power gain is large, and the noise is low. Therefore, the wide band low noise amplifier or the microwave band oscillation circuit is used. It is widely used for Further, since the electron mobility is high, the mutual conductance gm is also large, and there are advantages that it operates at high speed and consumes less power because of its small series resistance and small parasitic capacitance. 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 the resistance 5
The DC power supply V _GG is applied from the terminal 58 via the bias circuit constituted by 2 and the resistor 53. Feedback resistor 5
When there is no 4, the signal input to FET3 is FET3
Is amplified by the voltage amplification degree determined by the product of the mutual conductance gm of the load resistance 56 and the resistance value of the load resistance 56, and is output from the output terminal 2 via the DC blocking capacitor 57 provided on the output side. Generally, negative feedback is widely used in an amplifier circuit for the purpose of improving stability against power supply fluctuations, absorbing characteristic fluctuations due to transistor variations, improving non-linear distortion, and broadening the bandwidth. As shown in FIG. 4, a circuit type is known in which a feedback resistor 54 for performing voltage feedback from the drain to the gate of the FET 3 is inserted to form a feedback path. The capacitor 55 is for cutting off the DC component of the feedback path. The amount of feedback is resistance 5
It is almost determined by the voltage division ratio of the impedance value obtained by paralleling the output impedance of the input signal source 2 with the resistor 53 and the resistance value of the feedback resistor 54.

[Problems to be solved by the invention]

In the above-described conventional feedback amplifier circuit, it is difficult to make the bandwidth wider than a certain amount due to the capacitance of the field effect transistor itself, and further, since the feedback path is connected to the input signal path, the input impedance of the feedback amplifier circuit is increased. Since it is impossible to independently set the feedback amount and the feedback amount, it takes a lot of time to design the circuit, and the range in which the input impedance and the feedback amount can be set is considerably restricted. Further, when the negative feedback amplifier circuit as shown in FIG. 4 is used as the front end amplifier of the high-speed optical receiver circuit, the band characteristic of the output signal of the amplifier circuit is deteriorated by the time constant of the capacitance and load resistance of the photodetector. It is a characteristic. Conventionally, in order to improve this point, a means has been taken in which an equalization circuit composed of C and R is connected to the amplification circuit shown in FIG. 4 and further amplified. However, in the case of this means, there are drawbacks such as characteristic deterioration due to multistage connection of amplifier circuits and increase in the number of amplification stages. As another means, an inductance is inserted between the load resistor 56 of the amplifier circuit of FIG. 4 and a terminal 59 to which a DC power source of the voltage V _DD is supplied to form a series peaking circuit with the inductance, and a band is formed. There is a means of compensation. However, even with this means, the stray capacitance is increased by using in the direction of increasing the inductance value in order to secure good characteristics, and as a result, the self-resonant frequency is lowered, and good characteristics cannot be obtained. is there. Also, when considering the realization of a wide band amplifier up to the GB / S band (-10 GHz), the [S21] characteristic of the transistor is approximately 6 DB /
Since it decreases with OCT, it is impossible to secure a sufficient band with only a CR coupling amplifier. Also,
Even if negative feedback is applied, the band is widened but the gain is reduced. Furthermore, even if a peaking circuit is used, it only works to raise the upper limit band, and therefore there are many drawbacks in that it is difficult to extend the band to the high frequency side.

An object of the first invention is to eliminate the above-mentioned drawbacks and to provide a negative feedback amplifier circuit in which the input impedance and the feedback amount can be set independently of each other and which has a wide band and is easy in circuit design. Another object of the present invention is to provide a negative feedback amplifier circuit which has two band compensation circuits and realizes band compensation for a high band by dividing the band compensation characteristic and has a wide frequency characteristic.

A second object of the present invention is to eliminate the above-mentioned drawbacks and to make the gate voltage of the field effect transistor to which the feedback signal is applied variable without changing the resistance voltage division ratio that determines the feedback amount, and yet to achieve a wide band. An object of the present invention is to provide a negative feedback amplifier circuit whose gain can be changed.

A third object of the present invention is to provide a negative feedback amplifier circuit which eliminates the above-mentioned drawbacks and which allows a part of the feedback path to be variably gained so that the gain can be varied over a wide band.

[Means for solving problems]

A negative feedback amplifier circuit according to a first aspect of the present invention includes a first band compensating circuit formed by connecting a first resistor and a capacitor in parallel, a second resistor and an inductor connected in series, and inputting together with the first band compensating circuit. A second band compensation circuit for compensating the band characteristic for the signal, a first distributed constant line for impedance matching with the input signal, and a second distributed constant line for performing impedance conversion for setting the impedance for the input signal and a third line. And a low pass microwave impedance matching / converting circuit having the resistance of, and the output of the low pass microwave impedance matching / converting circuit being input to the gate, and the drain being the second band compensating circuit. A first field effect transistor having a source connected to the power supply terminal 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 output signals from the drains of the first and second field effect transistors. A feedback circuit for negatively feeding back the gate of the field effect transistor.

A negative feedback amplifier circuit according to a second aspect of the present invention comprises a first band compensation circuit formed by connecting a first resistor and a capacitor in parallel, and a second resistor and an inductance connected in series, together with the first band compensation circuit. A second band compensation circuit that compensates the band characteristic for the input signal, a first distributed constant line that performs impedance matching for the input signal, and a second distributed constant line that performs impedance conversion for setting the impedance for the input signal and a second distributed constant line. A low-pass microwave band impedance matching / converting circuit having three resistors;
The output of the low pass microwave impedance matching / converting circuit is input to the gate, and the drain is connected to the power supply terminal via the second band compensation circuit and the source is connected to the first band compensation circuit. A first field-effect transistor grounded via a drain, a second field-effect transistor having a drain connected to the drain of the first field-effect transistor and a source grounded, and the first and second field-effect transistors A feedback circuit having a variable DC power source for negatively feeding back the output signal from the drain of the second field effect transistor to the gate of the second field effect transistor and changing the gate potential of the second field effect transistor.

Furthermore, the negative feedback circuit of the third invention comprises a first band compensating circuit formed by connecting a first resistor and a capacitor in parallel, and a second resistor and an inductance connected in series, and is input together with the first band compensating circuit. A second band compensation circuit for compensating the band characteristic for the signal, a first distributed constant line for impedance matching with the input signal, and a second distributed constant line for performing impedance conversion for setting the impedance for the input signal and a third line. And a low pass microwave impedance matching / converting circuit having the resistance of, and the output of the low pass microwave impedance matching / converting circuit being input to the gate, and the drain being the second band compensating circuit. A first field effect transistor connected to a power supply terminal via the source and 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 output signals from the drains of the first and second field-effect transistors. And a variable feedback circuit having a variable resistance that negatively feeds back to the gate of the field effect transistor and changes the amount of the negative feedback.

〔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. In the embodiment of FIG. 1, the first and second field effect transistors FET31 and FET32 are connected in parallel with each other in parallel, and receive a input signal to perform impedance matching with respect to the input signal. A low-pass microwave band impedance matching circuit 511 as a constant line, and a second low-pass microwave band impedance conversion circuit 531 as a second distributed constant line having a microstrip line configuration for performing impedance conversion on an input signal. A low pass microwave band impedance matching / converting circuit 50 having a resistor 53 as a third resistor is connected to apply an input signal via a capacitor 51, and an output signal is applied to the gate of the FET 32 via a feedback circuit 10. Of the FET 31 The over scan be grounded to the ground through a band compensation circuit 1000 as the first band compensation circuit constituted by parallel connection of the resistor 102 as a first resistor and a capacitor 101, and further connected in parallel FET
A second band compensation circuit 1001 in which a second resistor 56 and an inductance 103 are connected in series is provided between the drains of 31 and ET32 and the DC power supply V _DD, and FET 31 and FET 3 are provided.
The load is 2. In FIG. 1, FETs 31 and 3
The second DC power supply V _DD is applied from the terminal 59 via the resistor 56 and the inductance 103. The resistor 56 and the inductance 103 form a series peaking circuit. The resistor 56 may be a passive element like a normal resistor or an active element including a FET. Capacitor 5
Reference numerals 1, 57 and 55 are capacitors for cutting off direct current. In the figure, an example of AC coupling is shown as an example of the configuration of the feedback circuit 10. The DC signal of the input signal input to the input terminal 1 is blocked by the capacitor 51, and the FE
Input to the gate of T31. The low-pass microwave band impedance matching circuit 511 in the low-pass microwave band impedance matching / converting circuit 50 is a lossless matching circuit, and the impedance looking into the signal source side at the upper limit of the band is complex at any cutting plane. The condition is set so that the power reflection coefficient [S] ² becomes zero due to the conjugate relation. The resistor 53 determines the input impedance, but in the microwave band, it is converted to high impedance by the low pass microwave band impedance conversion circuit 531 and has almost no effect on the main line. Therefore, the impedance matching by the lossless circuit is sufficiently performed, and the maximum available power gain of the FET 31 is obtained at the upper limit of the band. The DC gate potential of the FET 31 is the terminal 5
_Provided by a bias circuit consisting of a resistor 52 connected via 8 to a DC power supply of voltage V _GG . FET3
The signal amplified by 1 and output to the drain has its DC component blocked by the capacitor 57 and is output from the output terminal 2. The frequency characteristic of the output signal has a peaking characteristic determined by the capacitor 101 and the resistor 102 of the band compensation circuit 1000 and the inductance 103 and the resistor 56 of the band compensation circuit 1001, and the band is further improved by this. Has wideband characteristics. The values of the inductance 103, the resistor 56, the capacitor 101, and the resistor 102 can be appropriately selected according to desired characteristics. On the other hand, the gate of the FET 32 has a feedback circuit 10
A part of the output signal is input through the feedback resistor 54.
The phase of this signal is the inversion of the phase of the input signal at the input end 1.

The gate potential of the FET 32 is supplied to the terminal 5 via the bias circuit composed of the resistor 11 and the resistor 12 of the feedback circuit 10.
8 is supplied from a current source connected to the power source. The magnitude of the signal fed back to the FET 32 is substantially determined by the ratio between the resistance value of the resistors 11 and 12 arranged in parallel and the resistance value R ₅ of the feedback resistor 54. In the case of the circuit configuration shown in FIG.
Since 31 and FET 32 are connected in parallel, FE
The load resistance value of T31 is the resistance 56 in which the input resistance of the feedback circuit 10 and the operating resistance of the FET 32 are connected in parallel.

In the circuit shown in FIG. 1, the FET 31 and the FET 32 are connected in parallel, and the input signal is fed to the gate of the FET 31 by the FET.
The gate of 32 has a configuration in which a feedback signal is input respectively. Therefore, the input signal path and the feedback path can be separated, and the input impedance and the feedback amount can be independently set to desired values, which facilitates circuit design. In this case, the value of the input impedance is generally determined by the resistor 53 because the input impedance of the FET is usually extremely high. Further, since the circuit shown in FIG. 1 has two band compensation circuits and an impedance matching circuit, each band compensation capability is reduced,
In addition, because the compensation range can be changed,
The compensation band can 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 the FETs 31 and 32 are connected in parallel, and the gate of the FET 31 has a capacitor 51,
An input signal is applied via the low pass microwave impedance matching / converting circuit 50, a part of the output signal is applied to the gate of the FET 32 via the feedback resistor 54, and a voltage is applied as the gate bias DC voltage of the FET 32. V
A variable direct-current voltage source 13 of _CONT is provided, and the source of the FET 31 is grounded to the ground via a band compensation circuit 1000 composed of a capacitor 101 and a resistor 102 connected in parallel, and the FET 31 and FET 3 are connected in parallel.
A band compensating circuit 1001 including an inductance 103, a resistor 56 and a series circuit is provided between the drain of 2 and the DC power source 59 of the voltage V _DD , and is configured as a load of the FET 31 and the FET 32.

The signal input to the input terminal 1 is amplified by the FET 31, the direct current component is blocked by the capacitor 57, and is output from the output terminal 2. The frequency characteristic of the output signal is a peaking characteristic determined by the band compensating circuits 1000 and 1001 and a wide band characteristic in which the band is improved by the low pass microwave band impedance matching / converting circuit 50.

The FET of the FET 32 is connected to the gate of the FET 32 via the feedback resistor 54.
A part of the output signal of 31 is input. The DC gate bias voltage of the FET 32 is the variable DC power supply 13 of the voltage V _CONT.
It becomes a value obtained by dividing the output voltage of 1 by the resistance 11 and the resistance 12. In the circuit of FIG. 2, FET31 and FET32
Is connected in parallel, the load resistance value of the FET 31 is the load resistance 56, the input resistance of the variable feedback circuit 20 and the F
It is connected in parallel with the operating resistance of ET32.

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 of the resistors 11 and 12, changes. With this FET
The DC operating point of 32 changes, which changes the transconductance of FET 32. 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. Since this variable gain amplifier circuit does not use a variable resistance element that easily causes parasitic impedance, it has a feature that the gain can be changed without degrading the frequency characteristic of the gain even if the gain amount is largely changed. According to this embodiment, it is possible to configure a so-called AGC circuit which always obtains a constant output signal level by changing the gain in response to the fluctuation of the input signal level, and the input impedance and the feedback amount are independently set. It is possible to obtain a wider-band negative feedback amplifier circuit capable of Furthermore, there is a feature that the circuit design is easy.

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

FIG. 3 is a circuit diagram showing an embodiment of the third invention. In the embodiment shown in FIG. 3, the drains of the FET 31 and the FET 32 are connected, and the capacitor 51,
An input signal is applied through the low pass microwave impedance matching / converting circuit 50, and a part of the output signal is applied to the gate of the FET 32 through the variable feedback circuit 30, and the band compensating circuit 1000 is further provided. , Band compensation circuit 1
001 is provided.

The configuration of FIG. 3 uses a variable resistor 541 instead of the feedback resistor 54 in the circuit of FIG. FET3
The feedback signal to 2 is the variable resistor 541 of the variable feedback circuit 30.
Is applied via. The feedback amount at this time is applied via the variable resistor 541 of the variable feedback circuit 30. The amount of feedback at this time is determined by the ratio between the resistance value R _fv of the variable resistor 541 and the parallel connection value of the resistors 11 and 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 the FET 32 is the resistance 11 and the resistance 12
Therefore, even if the variable resistor 541 is changed, the DC gate potential of the FET 32 is kept constant. Third
Also in the circuit shown in the figure, as in the circuit shown in FIG. 1, the band compensation circuit 1000, 1001 and the low pass microwave band impedance matching / converting circuit 50 provide a wider frequency characteristic. Further, the input signal path and the feedback path can be separated from each other, and the wideband negative feedback amplifier circuit in which the input impedance and the feedback amount can be independently set can be obtained. Further, by using the circuit of FIG. 3, it is possible to configure a so-called AGC circuit in which the gain is changed corresponding to the fluctuation of the input level and a constant output signal level is always obtained.

In the above description, the case where a GaAs-FET is used as an FET suitable for forming a wide band amplifier circuit has been described, but the scope of the present invention is not limited to this, and a case of using a silicon FET is also possible. It goes without saying that the same applies.

〔The invention's effect〕

As described above, according to the first aspect of the invention, the drains of two FETs are connected in parallel as a wide band amplification circuit using FETs, and the gate of one FET is matched with a low pass microwave band impedance. / Applying an input signal via the conversion circuit, applying a feedback signal to the gate of the other FET, and connecting a band compensation circuit consisting of a resistor and a capacitor between the source of the FET to which the input signal is applied and the ground. In addition, the input impedance and the feedback amount can be set independently by connecting and using the band compensation circuit including the inductance and the resistance between the drain connected to the two FETs and the DC voltage source. Therefore, it is possible to obtain a negative feedback amplifier circuit which realizes a band compensation characteristic for a wide band, has a wide band characteristic, and has good stability.

According to the second invention, the gain is variable and the input impedance and the feedback amount are changed by changing the DC gate bias voltage of the FET that applies the feedback signal in the circuit of the first invention by using the variable DC voltage source. There is an effect that a negative feedback amplifier circuit that can be set independently and has good frequency characteristics can be obtained.

Further, according to the third invention, by using a variable resistor as a feedback resistor in the feedback path of the wideband negative feedback amplifier circuit according to the first invention, the gain is variable and the input impedance and the feedback amount can be set independently and stable. There is an effect that a negative feedback amplifier circuit having excellent frequency characteristics and excellent in frequency characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the first invention, FIG. 2 is a circuit diagram showing one embodiment of the second invention, and FIG. 3 is a diagram showing one 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 ... Resistance, 54 ... Feedback resistance, 541 ...
Variable resistance, 51, 57, 55, 101 ... Kendanser,
103 ... Inductance, 1000 ... First band compensation circuit, 1001 ... Second band compensation circuit, 50 ... Low pass microwave impedance matching / converting circuit,
511 ... Low-pass microwave impedance matching circuit 531 ... Low-pass microwave impedance conversion circuit.

Claims (3)

[Claims] 1. A first band compensating circuit comprising a first resistor and a capacitor connected in parallel, and a second resistor and an inductor connected in series to compensate the band characteristic for an input signal together with the first band compensating circuit. A second band compensation circuit that
A low-pass microwave band impedance matching / having a first distributed constant line for impedance matching with respect to an input signal, a second distributed constant line for impedance conversion for setting impedance with respect to the input signal, and a third resistance The output of the conversion circuit and the low-pass microwave band impedance matching / conversion circuit is input to the gate, the drain is connected to the power supply terminal through the second band compensation circuit, and the source is the first band. A first field effect transistor grounded through a compensation circuit; a second field effect transistor having a drain connected to the drain of the first field effect transistor and a source grounded; and the first and second field effect transistors. The output signal from the drain of the field effect transistor is applied to the gate of the second field effect transistor. And a feedback circuit for negatively feeding back, the negative feedback amplifier circuit, characterized in that the output signal obtained by amplifying the input signal by band compensation and to obtain from the connecting drains of said first and second field-effect transistor. 2. A first band compensation circuit formed by connecting a first resistor and a capacitor in parallel, and a second resistor and an inductance connected in series to compensate the band characteristic for an input signal together with the first band compensation circuit. A second band compensation circuit that
A low-pass microwave band impedance matching / having a first distributed constant line for impedance matching with respect to an input signal, a second distributed constant line for impedance conversion for setting impedance with respect to the input signal, and a third resistance The output of the conversion circuit and the low-pass microwave band impedance matching / conversion circuit is input to the gate, the drain is connected to the power supply terminal through the second band compensation circuit, and the source is the first band. A first field effect transistor grounded through a compensation circuit; a second field effect transistor having a drain connected to the drain of the first field effect transistor and a source grounded; and the first and second field effect transistors. The output signal from the drain of the field effect transistor is applied to the gate of the second field effect transistor. A feedback circuit having a variable DC power source that negatively feeds back and changes the gate potential of the second field effect transistor, and outputs an output signal obtained by band-compensating the input signal and amplifying the output signal. A negative feedback amplifier circuit characterized by being obtained from the connection drain of a transistor. 3. A first band compensating circuit formed by connecting a first resistor and a capacitor in parallel, and a second resistor and an inductance connected in series to compensate the band characteristic for an input signal together with the first band compensating circuit. A second band compensation circuit that
A low-pass microwave band impedance matching / having a first distributed constant line for impedance matching with respect to an input signal, a second distributed constant line for impedance conversion for setting impedance with respect to the input signal, and a third resistance The output of the conversion circuit and the low-pass microwave band impedance matching / conversion circuit is input to the gate, the drain is connected to the power supply terminal through the second band compensation circuit, and the source is the first band. A first field effect transistor grounded through a compensation circuit; a second field effect transistor having a drain connected to the drain of the first field effect transistor and a source grounded; and the first and second field effect transistors. The output signal from the drain of the field effect transistor is applied to the gate of the second field effect transistor. A variable feedback circuit having a variable resistance for performing negative feedback and changing the amount of the negative feedback, and outputting an output signal obtained by band-compensating and amplifying the input signal from a connection drain of the first and second field effect transistors. A negative feedback amplifier circuit characterized by being obtained.