JPH0630413B2 - Wideband negative feedback amplifier circuit - Google Patents

Description

The present invention relates to a wide band negative feedback amplifier circuit.

(Prior Art) FIG. 5 is a circuit showing a conventional wideband negative feedback amplifier circuit. The figure shows a configuration example of a source-grounded one-stage wide band AC coupled negative feedback amplifier circuit using a gallium arsenide (hereinafter abbreviated as GaAs) FET as a field effect transistor (hereinafter abbreviated as FET). (References: Use Negative Feedback To Sash Wide Band VSW)
R), MICROWAVES Magazine, 197
October 7 (OCT.1977), Volume 17 (Vol.1)
7), N10). The GaAs-FET used in this circuit has the characteristics that the maximum oscillation frequency is much higher than the silicon bipolar transistor, the maximum effective power gain is large, and the noise is low. Widely used in microwave band oscillator circuits. In addition, since the electron mobility is high, the mutual conductance g _m
The advantages are that it operates at high speed and consumes less power because of its small series resistance and small parasitic capacitance. In FIG. 5, the DC component of the signal input to the input terminal 1 is cut off by the capacitor C ₁ , and F
Input to the gate of ET3. The gate potential of the FET 3 is applied from the DC power supply V _GG via a bias circuit constituted by the resistors R ₁ and R ₂ . Feedback resistor R
_When there is no _f , the signal input to FET3 is FET3
Is amplified by a voltage amplification degree determined by the product of the mutual conductance g _m of the load resistance _RL and the load resistance R _L , and is output from the output end 2 via the DC blocking capacitor C ₂ provided on the output side. In general, it is widely used to provide negative feedback to 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 further broadening the band. As the fifth
As shown in the figure, there is known a circuit type in which a resistor R _f for performing voltage feedback from the drain of the FET 3 to the gate is inserted to form a feedback path. The capacitor C _f is for blocking the DC component of the feedback path. The feedback amount is substantially determined by the voltage division ratio between the feedback resistor R _f and the impedance value in which the resistors R ₁ and R ₂ are parallel to the output impedance of the input signal source.

(Problems to be solved by the invention) However, in such a conventional feedback amplifier circuit, it is difficult to increase the bandwidth to a certain extent or more due to the capacitance of the field effect transistor itself, and further, the feedback path is an input signal path. Therefore, it is impossible to set the input impedance and the feedback amount of the feedback amplifier circuit independently of each other, and it takes a lot of time to design the circuit, and the input impedance and the feedback amount can be set within the settable range. It had the drawback of being significantly constrained.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks and to provide a wideband negative feedback amplifier circuit in which the input impedance and the feedback amount can be set independently, and the wideband and the circuit design are easy.

(Means for Solving the Problems) In order to solve the above-mentioned problems, a wideband negative feedback amplifier circuit provided by the present invention provides an input circuit for transmitting a first signal corresponding to an input signal and a drain to each other. An amplifier circuit having two connected field effect transistors as active elements, a feedback circuit for receiving a signal sent by the amplifier circuit and sending a feedback signal, and an output signal corresponding to the signal sent by the amplifier circuit An output circuit for applying the first signal to one of the gates of the two field effect transistors and the feedback signal to the other gate of the two field effect transistors. A band compensating circuit including a series circuit of an inductance and a resistance is provided to serve as the load impedance of the two field effect transistors.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. In this embodiment, the drains of the FETs 31 and 32 are connected in parallel with each other, and the gate of the FET 31 has a capacitor C.
_The input signal is applied via ₁ and a part of the output signal is applied to the gate of the FET 32 via the feedback circuit 10. Furthermore, the drains of the FET 31 and FET 32 connected in parallel and the DC power supply V _DD are connected. Inductance L _P and resistance R
_A band compensation circuit 100 including a series circuit of _L
31 and the load of the FET 32.

In this embodiment, the DC bias of the FETs 31 and 32 is applied from the DC power supply V _DD via the resistor R _L and the inductance L _P. The resistor R _L and the inductance L _P form a series peaking circuit. The resistor R _L may be a passive element like a normal resistor or an active element including a FET. The capacitors C ₁ , C ₂ and C _f are all capacitors for DC blocking. In this embodiment, the feedback circuit 10 is an example of a circuit using AC coupling.

The input signal input to the input terminal 1 has its DC component blocked by the capacitor C ₁ and is input to the gate of the FET 31. The DC gate potential of the FET 31 is applied from the DC power supply V _GG via the bias circuit composed of the resistors R ₁ and R ₂ . The signal amplified by the FET 31 and output to the drain has its DC component blocked by the capacitor C ₂ and is output from the output terminal 2. The frequency characteristic of the output signal is a wide band characteristic in which the band is improved by the peaking characteristic determined by the inductance L _P and the resistance R _L of the band compensation circuit 100. This inductance L _P
It is necessary to properly select the values of the resistance R _L and the resistance R _L according to the desired characteristics. On the other hand, at the gate of FET 32,
A part of the output signal is input via the feedback resistor R _f of the feedback circuit 10. 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 applied from the DC power supply V _GG via the bias circuit formed by the resistors R ₃ and R ₄ of the feedback circuit 10. FE
The magnitude of the signal fed back to T32 depends on the resistances R ₃ and R _3.
It is almost determined by the ratio between the resistance value of ₄ and the resistance value of the feedback resistance R _f . In the case of the circuit configuration of FIG.
Since the FET 31 and the FET 32 are connected in parallel, the load resistance value of the FET 31 is equal to the resistance R _L of the feedback circuit 1.
The input resistance of 0 and the operating resistance of the FET 32 are connected in parallel. Therefore, the open circuit voltage gain is FET3
It is determined by the relationship between the transconductance g _{m of} 1 and the load resistance value of the FET 31.

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, since the input impedance of the FET is usually extremely high, the value of the input impedance is determined by the resistance R ₁ and the resistance R ₂ in parallel.

Next, a second embodiment of the present invention will be described with reference to FIG.

In the embodiment of FIG. 2, the drains of the FETs 31 and 32 are connected in parallel, an input signal is applied to the gate of the FET 31, and a part of the output signal is applied to the gate of the FET 32 via a feedback resistor and the FET 32 is applied. A variable DC voltage source V _CONT is provided as the gate bias DC voltage of, and the drains of the FET 31 and FET 32 connected in parallel and the DC power source V
The band compensation circuit 100 comprising a series circuit of inductance _{L P} and resistor _{R L} between the _DD provided FET31 and FET3
There is a load of 2.

The signal input to the input terminal 1 is amplified by the FET 31, the DC component is blocked by the capacitor C ₂ , and is output from the output terminal 2. The frequency characteristic of the output signal is a wide-band characteristic in which the band is improved by the peaking characteristic determined by the inductance L _P and the resistance R _L of the band compensation circuit 100. This inductance L _P
It is necessary to select appropriate values for the resistance and the resistance R _{L according} to the desired characteristics. In the gate of FET32,
A part of the output signal of the FET 31 is input via the feedback resistor R _f . The DC gate bias voltage of the FET 32 is a value obtained by dividing the output voltage of the variable DC voltage source V _CONT 13 by the resistors R ₃ and R ₄ . Since the FET 31 and the FET 32 are connected in parallel in the circuit of FIG. 2, the load resistance value of the FET 31 is such that the input resistance of the variable feedback circuit 20 and the operating resistance of the FET 32 are connected in parallel to the load resistance R _L 56. It will be what you did.

Now, when the output voltage of the variable DC power supply V _CONT 13 is changed, the FET determined by the voltage division ratio of the resistors R ₃ and R ₄
The DC gate bias voltage of 32 changes. As a result, the DC operating point of the FET 32 changes, and therefore the FET 3
The transconductance of 2 changes. Therefore, the voltage transfer function of the negative feedback circuit, in other words, the amount of feedback can be changed. That is, the gain of the negative feedback amplifier circuit can be made variable by using the variable DC voltage source V _CONT 13. Since this variable gain amplifier circuit does not use a variable resistance element that easily causes parasitic impedance, it has a characteristic that the frequency characteristic of the gain can be kept almost flat even if the gain amount is largely changed.

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 set the input impedance and the feedback amount independently of each other. A possible wideband negative feedback amplifier circuit is obtained. Furthermore, there is a feature that the circuit design is easy.

Next, a third embodiment of the present invention will be described with reference to FIG.

In the embodiment shown in FIG. 3, the drains of the FETs 31 and 32 are connected in parallel, and an input signal is applied to the gate of the FET 31, and F
A part of the output signal is fed to the variable feedback circuit 3 at the gate of ET32.
0, and the band compensation circuit 100
Is the load of the FET 31 and the FET 32.

The configuration of FIG. 3 uses a variable resistor R _fv instead of the feedback resistor R _f in the circuit of FIG. FET32
The feedback signal to the variable feedback circuit 30 is applied via the variable resistance R _fv of the variable feedback circuit 30. The feedback amount at this time is determined by the ratio between the resistance value of the variable resistor R _fv and the parallel connection value of the resistors R ₃ and R ₄ .

Therefore, in the embodiment of FIG. 3, the amount of feedback is changed by changing the variable resistance R _fv, and the gain of the amplifier circuit can be made variable. The DC gate potential of the FET 32 is also set by the resistors R ₃ and R _4, so the variable resistor R
_{Even if fv} is changed, the DC gate potential of the FET 32 is kept constant. In the circuit of FIG. 3 as well, as in the circuit of FIG. 1, the band widening of the frequency characteristic can be obtained by the band compensation circuit 100. Further, the input signal path and the feedback path can be separated, and a wideband negative feedback amplifier circuit in which the input impedance and the feedback amount can be independently set can be obtained. Further, there is a feature that the circuit design is easy. Further, by using the circuit of FIG. 3, it is possible to configure a so-called AGC circuit in which the gain is changed in response to the fluctuation of the input signal level to always obtain a constant output signal level.

FIG. 4 is a circuit diagram showing a modification of the embodiment shown in FIG. 3 (third embodiment). In the circuit of FIG. 3, a variable resistor R _fv is provided between the output signal path and the gate of the FET 32 to form a capacitor C _f.
The variable resistor R _{fv of} FIG. 3 is a fixed resistor R _f as in the circuit of FIG. 4, and the capacitor C is connected between the gate of the FET 32 and the ground. _Even if the variable feedback circuit 40 that connects the variable resistor R _fv via ₅ to make the feedback amount variable is used, the gain variable wide band negative feedback amplifier circuit can be obtained as in the circuit of FIG.

(Effects of the Invention) As described above, according to the present invention, a wide band amplifier circuit using FETs as active elements is used. In this wide band amplifier circuit, the drains of two FETs are connected to each other and one of the F
The input signal is applied to the gate of ET and the feedback signal is applied to the gate of the other FET.
By connecting and using a band compensation circuit consisting of an inductance and a resistance between the drain DC power supply connected to and, the input impedance and the feedback amount can be set independently of each other, and a wide band characteristic is provided. Moreover, a wideband negative feedback amplifier circuit with good stability can be 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 particularly described, but the scope of the present invention is not limited to this, and a case where a silicon FET is used is also described. It goes without saying that the same applies.

[Brief description of drawings]

1 to 3 are circuit diagrams respectively showing first to third embodiments of the present invention, FIG. 4 is a circuit diagram showing a modification of the embodiment of FIG. 3, and FIG. 5 is a conventional wide band. It is a circuit diagram which shows a negative feedback amplifier circuit.

Claims (3)

[Claims] 1. An input circuit which sends out a first signal corresponding to an input signal, an amplifier circuit which uses two field effect transistors whose drains are connected to each other as active elements, and a signal which is sent out by the amplifier circuit. A feedback circuit for sending a feedback signal and an output circuit for sending an output signal corresponding to the signal sent by the amplifier circuit, and one of the two field effect transistors has the gate of the first The feedback signal is applied to the other gate of each signal, and a band compensating circuit including a series circuit of an inductance and a resistance is provided between the drain and the DC power source to set the load impedance of the two field effect transistors. A wideband negative feedback amplifier circuit characterized in that. 2. The feedback circuit comprises a variable voltage DC power supply,
The broadband negative feedback amplifier circuit according to claim 1, wherein the output of the variable voltage DC power supply is applied as a gate bias DC voltage to the gate to which the feedback signal is applied. 3. The feedback circuit according to claim 1, wherein a level ratio between the amplification circuit transmission signal and the feedback signal is determined by a resistance value of a variable resistor which receives the amplification circuit transmission signal. A wideband negative feedback amplifier circuit according to the item.