JPS61210710A - Amplifying circuit for wide band negative feedback - Google Patents

Abstract

PURPOSE:To set respectively independently input impedance resistance and a feedback quantity and to obtain a wide band characteristic by connecting and using a band compensating circuit composed of a capacitor and a resistance between a source and a ground of an FET to impress an input signal. CONSTITUTION:The drains of FET 31 and 32 are respectively connected in parallel, an input signal is impressed through a capacitor C151 to a gate of the FET 31 and part of the output signal is impressed through a feedback circuit 10 to a gate of the FET 32. Further, a source of the FET 31 is earthed on the ground through a band compensating circuit 100 composed of the parallel connection with a capacitor CP101 and a resistance 102. Consequently, the device has the peaking characteristic determined by the capacitor CP101 and the resistance RP102 of the band compensating circuit 100, and thus, the wide band characteristic whose band is improved is obtained. In such a way, the FET 31 and the ET 32 are connected in parallel, and to the gate of the FET 31, the input signal is inputted and to the gate of the FET 32, a feedback loop is inputted respectively, and therefore, the input signal and the feedback loop can be separated, and the input impedance and the feedback quantity can be respectively independently set to the prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a broadband J-type feedback amplifier circuit.

(1 American Technology) FIG. 5 is a circuit diagram showing a conventional wideband r1 feedback amplifier circuit. The figure shows a field effect transistor (hereinafter Ii'
gallium arsenide (hereinafter referred to as G
This figure shows an example of the configuration of a single-stage broadband AC-coupled negative feedback amplifier circuit using FETs (abbreviated as aAs). (Reference “Use Negative Feedb
ack To 5lashWidebandVSWII
“MICROWAVESOCT1977, vo] 17
(Refer to NIO) The GaAs-FET used in this circuit has characteristics such as a much higher maximum oscillation frequency, a large maximum available power gain, and low noise compared to silicon bipolar transistors, so it has a wide band and low noise. It is widely used in amplifiers, microwave band oscillation circuits, etc.

Also, because the mobility of electrons is large, the mutual conductance gn
l is also large, and because of the small series resistance and small parasitic capacitance, there are advantages of high speed operation and low power consumption.

In FIG. 5, the DC component of the signal input to the input terminal 1 is blocked by the capacitor C151, and the signal is input to the gate of the FET3. The gate potential of FET3 is the resistor R1
52 and R253, it is applied to the DC power supply V from o. Feedback resistor R554
If there is no signal, the signal input to FET 3 is amplified by the voltage amplification value determined by the product of the mutual conductance gm of FET 3 and the load resistance R, 56, and is amplified by the voltage amplification value determined by the product of the mutual conductance gm of FET 3 and the load resistance R, 56, and is then amplified by the voltage amplification value determined by the product of the mutual conductance gm of FET 3 and the load resistance R, 56, and is then amplified by the voltage amplification value determined by the product of the mutual conductance gm of FET 3 and the load resistance R, 56. It is output from the output end 2. In general, applying negative feedback to amplifier circuits is widely used to improve stability against power supply fluctuations, absorb characteristic fluctuations due to transistor variations, improve nonlinear distortion, and further widen the bandwidth. However, as an example, as shown in FIG. 5, there is a known circuit type in which a resistor R54 is inserted to provide a feedback path for voltage feedback from the drain to the gate of the FET 3. The capacitor C, 55 is for blocking and analyzing the direct current component of the feedback path. The amount of feedback is approximately determined by the voltage division ratio between the impedance value obtained by connecting the resistor R152, the Jlk resistor R253, and the output impedance of the input signal source in parallel, and the feedback resistor R,54.

(Problems with the prior art) However, in such conventional feedback amplifier circuits, it is difficult to increase the bandwidth beyond a certain level due to field effects, the capacitance of the transistor itself, etc., and furthermore, the feedback path is connected to the input signal path. Because of this, it is impossible to independently set the input impedance and feedback amount of the feedback amplifier circuit, which requires a lot of effort in circuit design, and the range in which the input impedance and feedback amount can be set is quite limited. It had the disadvantage of being subject to restrictions.

(Objective of the Invention) A first object of the present invention is to provide a wideband negative feedback amplifier circuit that eliminates the above-mentioned drawbacks and can independently set the input impedance and the amount of feedback, and has a wideband and easy circuit design. be.

A further object of the second invention is to eliminate the above-mentioned drawbacks and to make it possible to achieve a wide band and a gain by making the gate voltage of the field effect transistor to which the feedback signal is applied variable, without changing the resistor voltage division ratio that determines the amount of feedback. The object of the present invention is to provide a wideband negative feedback amplifier circuit that can make the output variable.

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

(Structure of the Invention) According to the present invention, an input circuit that sends out a first signal corresponding to a human input signal, an amplifier circuit including two field effect transistors whose drains are connected in parallel, and the amplifier circuit include: a feedback circuit that receives a signal to be sent out and sends out a feedback signal; and an output circuit that sends out an output signal corresponding to the signal sent out by the amplifier circuit; The first signal is applied to the other gate, and the feedback signal is applied to the other gate.
The source of the field effect transistor that inputs the signal is grounded via a band compensation circuit configured by parallel connection of resistor R5 and capacitor C, and the source of the other field effect transistor is grounded directly. A wideband f1 feedback amplifier circuit characterized by the following can be obtained. 9. According to the present invention, an input circuit that sends out a first signal corresponding to an input signal, and two electric circuits whose drains are connected in parallel are used. an amplifier circuit equipped with an effect transistor; a variable feedback circuit equipped with a DC power supply capable of varying a gate voltage;
an output circuit that sends out an output signal corresponding to the signal sent out by the amplification circuit, and the gate of one of the two field effect transistors receives the first signal; Feedback signals are applied to each of the field effect transistors, and the source of the field effect transistor to which the first signal of the two field effect transistors is input is connected to a band J or a compensation circuit formed by a parallel connection of a resistor R and a capacitor C. A broadband negative feedback amplifier circuit is obtained, which is characterized in that the source of the other field effect transistor is connected directly to the ground.

Furthermore, according to the present invention, an input circuit that sends out a first signal corresponding to an input signal, and two IS lanes connected in parallel.
an amplifier circuit equipped with field effect transistors, and irJ
The variable feedback circuit includes a variable resistance resistor and receives the signal sent out by the amplifying circuit and sends out a feedback signal, and the output circuit sends out an output signal corresponding to the signal sent out by the amplifying circuit, The first signal is applied to the gate 1 of one of the field effect transistors, and the feedback signal is applied to the other gate, and the first signal of the two field effect transistors is applied. The source of the input field effect transistor is grounded via a band compensation circuit configured by a parallel connection of a resistor R and a capacitor C, and the source of the other field effect transistor is directly grounded. A broadband negative feedback amplifier circuit is obtained.

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

In Figure 1, trains of FET31 and FET32 are connected in parallel, and a capacitor C151 is connected to the gate of FET3.
A part of the output signal is applied to the gate of the FET 32 via the feedback circuit 10, and the source of the FET 31 is connected in parallel with a capacitor C, 101 and a resistor 102. Bandwidth compensation circuit 100
It is a figure which shows an example of the embodiment of the 1st invention which earthed to the ground via. In the same figure, FET
A DC bias of 31.32 is applied from a DC current DD59 via load resistors I), , 56. The load resistance P, , 56 may be a passive element such as a normal resistor, or an active element including an FET. Capacitors C151, C257, C, and 55 are all DC cutoff capacitors. In the figure, the feedback circuit 10
As an example of the configuration, an example of an embodiment using AC coupling is shown. The DC component of the input signal input to the input terminal 1 is blocked by the capacitor C151, and the input signal is input to the gate of the FET 31. The DC gate potential of FET31 is connected to the DC current ■o6 through a bias circuit consisting of resistors R152 and R253.
Added from 58. The DC component of the signal output to the train that is amplified by the FET3 is blocked by the capacitor C257, 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 the capacitor Cp101 and the resistor Rp102, and thereby has a wide band characteristic with an improved band. This capacitor C,10
It is necessary to appropriately select the values of resistor R1 and resistor R,1,02 according to the desired characteristics. On the other hand, a part of the output signal is input to the gate I of the FET 32 via the feedback resistor R154 of the feedback circuit 10. The phase of this signal is the inverted phase of the input signal at input terminal 1. FET32
The gate potential of the resistor R311 of the feedback circuit 10 and the resistor R
DC power supply V via a bias circuit composed of 412.

Added from o58.

The magnitude of the signal fed back to FET32 is determined by the resistance R311.
and the resistance value of the resistor R412 in parallel and the feedback resistor R45
It is almost determined by the ratio to the resistance value of 4. In the case of the circuit configuration shown in FIG. 1, FET 31 and FET 32 are connected in parallel, so the load resistance value of FET 31 is determined by the load resistance R1, 56, the input resistance of the feedback circuit 10, and the operating resistance of FET 32. They are connected in parallel. therefore,
The open circuit voltage gain is determined by the mutual conductance gm of FET31.
and the load resistance value of the above-mentioned FETa] and the band compensation circuit 100
It is determined by the relationship between the resistance Rp1.02 and the ratio. That is, since the open circuit voltage gain is reduced compared to the conventional circuit shown in FIG. 5, it is necessary to reduce the amount of feedback in the circuit shown in FIG. 1 in order to obtain a gain close to that of the circuit shown in FIG. The circuit shown in FIG. 1 has a configuration in which FET 31 and FET 32 are connected in parallel, and an input signal is input to the gate of FET 31, and a feedback signal is input to the gate of FET 32.

Therefore, the input signal 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 input impedance of the FET is usually extremely high, so the value of the human input impedance is determined by the resistor R152.
It is determined by the parallel value of R253 and resistor R253.

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

In Figure 2, the drains of FETs 31 and 32 are connected in parallel,
An input signal is applied to the gate of FET31, and FET32
A part of the output signal is applied to the gate of the transistor via a feedback resistor, and a variable DC voltage source VCONT1.3 is provided as a gate bias DC voltage of the FET 32.
Furthermore, the source of the FET 31 is connected to a band compensation circuit 100 consisting of a parallel connection of a capacitor C, 101 and a resistor 102.
FIG. 7 is a circuit diagram showing an example of an embodiment of the second invention, in which the power source is connected to the ground through the ground. The signal input to the input terminal 1 is amplified by the FET 31, the DC component is blocked by the capacitor C257, and the signal is sent to the output terminal 2.
is output from. The frequency characteristics of this output signal are
Capacitor C, 101 of band compensation circuit 100 and resistor 0
It has a peaking characteristic determined by 2, which results in an improved broadband characteristic. It is necessary to appropriately select the values of the capacitor C, 101 and the resistor R, 102 according to the desired characteristics. FET
FET 3 is connected to the gate of 32 via feedback resistor R, 54.
A part of the output signal of No. 1 is input. The DC gate bias voltage of FET32 is the value obtained by dividing the output voltage of variable DC voltage VCONT13 by resistor R311 and resistor R412.
Since it is connected in parallel with ET32, the load resistance value of FET31 is determined by the load resistance R, 56 and the variable feedback circuit 20.
The input resistance of FET 32 and the operating resistance of FET 32 are connected in parallel. Now, when the output voltage of the variable DC power supply VCONT], 3 is changed, the DC gate bypass voltage of the FET 32, which is determined by the voltage division ratio of the resistor R311 and the resistor R412, changes. This changes the DC operating point of FET 32 and therefore 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 current and voltage source VCONT13, the gain of the negative feedback amplifier circuit can be made variable. This variable gain amplification circuit uses a variable resistance element that tends to generate parasitic impedance, so it has the advantage that the frequency characteristics of the gain can be kept almost flat even if the amount of gain is changed greatly. 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, for example.
Furthermore, a wideband negative feedback amplifier circuit in which the input impedance and the amount of feedback can be set independently can be obtained. Another advantage is that circuit design is easy.

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

3 and 4 respectively show FET31. , 32 trains are connected in parallel, an input signal is applied to the gate of FET 31, a part of the output signal is applied to the gate of FET 32 via the variable feedback circuit 30 or 40, and The source of capacitor C, 101
The third circuit is connected to the ground via a band compensation circuit 100 consisting of a resistor R, 102 connected in parallel.
FIG. 2 is a circuit diagram showing an example of an embodiment of the illustrated invention. .

The circuit configuration in Figure 3 is based on the feedback resistor R that goes into the circuit in Figure 1.
154, a variable resistor RfV54.1 is used. ] i''ET32- feedback signal is applied via the variable resistor Rfv54 of the variable feedback circuit 30. At this time, the feedback
It is determined by the ratio to the parallel resistance value of resistor R412. However, by changing the variable resistor IfV541, the amount of feedback changes, and the gain of the amplifier circuit can be made variable.

The DC gate potential of FET32 is set by resistor R311 and resistor R4.
Therefore, even if the variable resistor Rfv54.1 is changed, the DC gate potential of I"ET32 is kept constant. In the circuit shown in FIG. A broadband characteristic can be obtained.Also, the input signal path and the feedback path can be separated, and a broadband 1-4 negative amplifier circuit can be obtained in which the input impedance and the amount of feedback can be set independently. , which has the advantage of easy circuit design.Also, by using the circuit described in Part 3, the so-called AG, which constantly obtains a constant output signal level by changing the gain in response to fluctuations in the input signal level, has the advantage of being easy to design.
A C circuit can be constructed. The circuit shown in FIG. 3 is of a type in which the amount of feedback is changed by connecting a variable resistor Rfv541 between the output signal path and the gate of FET 32 via capacitor A5, but unlike the circuit shown in FIG.
The variable resistor RfV in the figure is set as a fixed resistor RI-44, and the FET
By using a variable feedback circuit 40 in which a variable resistor R, 441 is connected between the gate of 32 and the ground via a capacitor C545 to make the amount of feedback variable, a broadband negative feedback circuit amplification circuit with gain = T can be obtained. .

(Effect of the invention) As explained in detail below, according to the first invention, the FE
As a wideband amplifier circuit using T, the drains of two FETs are connected in parallel, a human input signal is applied to the gate of one FET, a feedback signal is applied to the gate of the other FET, and the input By connecting and using a band compensation circuit consisting of a capacitor and a resistor between the source and toge lands of the FET to which the signal is applied, the input impedance and the amount of feedback can be set independently, and it has broadband characteristics. In addition, a broadband negative feedback circuit amplifier circuit with good stability can be obtained.

Furthermore, 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 the variable DC voltage source VCONT, the gain is variable and the input impedance and the amount of feedback can be adjusted. It is possible to obtain a wideband negative feedback circuit amplification circuit that can independently set and has good frequency characteristics.

Furthermore, according to the third invention, by using the variable resistor R4v as a feedback resistor in the feedback path of the broadband negative feedback circuit amplifier circuit in the first invention, the gain is variable and the input impedance and feedback amount can be set independently. As a result, a wideband negative feedback circuit amplifier circuit with good stability can be obtained.

In the above explanation, the case where a GaAs FET is used as a FET suitable for constructing a wideband amplifier circuit has been particularly described, but the scope of the present invention is not limited to this, and silicon FETs may also be used. Needless to say, the same applies to the case of using the same.

[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 circuit diagram showing an embodiment of the third invention. , FIG. 4 is a circuit diagram for explaining an embodiment of the third invention, and FIG. 5 is a circuit diagram showing a conventional broadband negative feedback circuit amplifier circuit. In the figure ゛3, 31.32...FET 52.53.
11: 12.10209. Resistor 54, 4406. Return 54□, 44□08. variable resistance
51, 57.101.55.45... Condenser 56-@load resistance 11... Input end 2... Output end 59.58... DC power supply 13
...Variable DC power supply Figure 1 Vl) D Figure 2 Figure 3 Vo. Figure 4 Vo. Figure 5

Claims (1)

[Claims] 1. An input circuit that inputs a first signal corresponding to an input signal, an amplifier circuit including two field effect transistors whose drains are connected in parallel, and a signal sent by the amplifier circuit. and an output circuit that sends out an output signal corresponding to the signal sent out by the amplifier circuit, and the gate of one of the two field effect transistors has the first The feedback signal is applied to the other gate of the field effect transistor, and the source of the field effect transistor to which the first signal of the two field effect transistors is input is connected to a resistor R and a capacitor C in parallel. 1. A wideband negative feedback amplifier circuit, characterized in that the source of the other field effect transistor is connected to the ground via a band compensation circuit configured by connection, and that the source of the other field effect transistor is directly connected to the ground. 2. The amplifier circuit includes an input circuit that sends out a first signal corresponding to the input signal, an amplifier circuit that includes two field effect transistors whose drains are connected in parallel, and a DC power supply that can vary the gate voltage. a variable feedback circuit that receives a signal to be sent out and sends out a feedback signal; and an output circuit that sends out an output signal corresponding to the signal sent out by the amplifier circuit, and the gate of one of the two field effect transistors. The first signal is applied to one gate, and the feedback signal is applied to the other gate, and the source of the field effect transistor to which the first signal is inputted is a resistor R and a capacitor. Grounded through a band compensation circuit configured by parallel connection with C,
A broadband negative feedback amplifier circuit characterized in that the source of the other field effect transistor is directly grounded. 3. An input circuit that receives a first signal corresponding to the input signal, an amplifier circuit that includes two field effect transistors whose drains are connected in parallel, and a variable resistor that receives the signal sent out by the amplifier circuit. a variable feedback circuit that sends out a feedback signal based on the feedback signal; and an output circuit that sends out an output signal corresponding to the signal sent out by the amplifier circuit; The feedback signal is applied to the other gate, and the first of the two field effect transistors is
The source of the field effect transistor that inputs the signal is grounded via a band compensation circuit formed by parallel connection of a resistor R and a capacitor C, and the source of the other field effect transistor is directly grounded. A wideband negative feedback amplifier circuit featuring: