JP2006025233A - Microwave amplifier circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a microwave amplifier circuit wherein the design flexibility of a bias circuit is enhanced and impedance conversion is made easy. <P>SOLUTION: In the microwave amplifier circuit wherein a stabilizing circuit 30 and a transistor 20 are connected in series to a signal path from an input terminal 41 to an output terminal 42, the stabilizing circuit 20 comprises; a first circuit having a first resistance 32 and a first capacitor 31 connected in parallel; a second circuit having a second resistance 34 and a second capacitor 33 having one end grounded, connected in series; and a short stub 36 having a third capacitor 35. The stabilizing circuit 30 has the first circuit connected in series between the input terminal 41 and an input electrode of the transistor 20 and has the second circuit and the short stub 36 connected in parallel between the input terminal 41 and the first circuit. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a microwave amplifier circuit including a stabilization circuit for preventing transistor oscillation.

  As a conventional microwave amplification circuit, there is a combination of a stabilization circuit composed of a capacitor and a resistor and a field effect transistor (FET) (see, for example, Patent Document 1). In the low frequency region, since the impedance of the capacitor is sufficiently higher than the resistance value of the resistor, a current flows through the resistor, the circuit loss increases, and stabilization can be achieved.

  On the other hand, in the high frequency region, the impedance of the capacitor is sufficiently smaller than the resistance value of the resistor, so that almost no current flows through the resistor and almost no circuit loss occurs. Therefore, the gain is not degraded at a desired frequency (high frequency region) having a high stability coefficient, and stabilization can be achieved in a region (low frequency region) where the FET has a low stability coefficient.

Japanese Patent Laid-Open No. 11-074740 (first page, FIG. 1)

  However, the prior art has the following problems. In the conventional microwave amplifier circuit, since a resistor is loaded in parallel with the FET, the input impedance of the microwave amplifier circuit is low, and there is a problem that impedance transformation is difficult when designing a matching circuit. Further, in the conventional microwave amplifier circuit, since the direct current is cut by the capacitor, the bias supply line can only be loaded between the FET and the capacitor, and there is a problem that the degree of freedom in designing the bias circuit is small. It was.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a microwave amplifier circuit that increases the degree of freedom in designing a bias circuit and facilitates impedance transformation.

  A microwave amplifier circuit according to the present invention is a microwave amplifier circuit in which a stabilization circuit and a transistor are connected in series on a signal path from an input terminal to an output terminal. The stabilization circuit includes a first resistor and a first capacitor. Are connected in parallel, a second circuit in which a second resistor and a second capacitor having one end grounded are connected in series, and a short stub having a third capacitor. The first circuit is connected in series between the input terminal and the input electrode of the transistor, and the second circuit and the short stub are connected in parallel between the input terminal and the first circuit. .

  According to the present invention, a bias can be supplied by connecting a resistor in parallel with a capacitor for stabilizing the high frequency region used in the stabilization circuit, thereby increasing the degree of freedom in designing the bias circuit. In addition, by connecting a short stub in parallel with the resistor for stabilizing the low frequency region and increasing the input impedance of the microwave amplifier circuit, a microwave amplifier circuit that facilitates impedance transformation is obtained. Can do.

Embodiment 1 FIG.
FIG. 1 is a circuit configuration diagram of a microwave amplifier circuit according to Embodiment 1 of the present invention. In FIG. 1, the microwave amplifier circuit 10 includes an FET 20 and a stabilization circuit 30. Further, the stabilization circuit 30 includes a short stub 36 including a first capacitor 31, a first resistor 32, a second capacitor 33, a second resistor 34, and a third capacitor 35. The microwave amplifier circuit 10 includes an input terminal 41 and an output terminal 42 as external input / output terminals.

  Here, the first capacitor 31 and the first resistor 32 are connected in parallel to form a first circuit. The second capacitor 33 and the second resistor 34 are connected in series to form a second circuit. The node 50 is directly connected to the input terminal 41, and indicates a connection point for explaining the connection relationship between the first circuit, the second circuit, and the short stub.

  The first circuit having the first capacitor 31 and the first resistor 32 is connected between the input side electrode of the FET 20 and the node 50. The second circuit having the second capacitor 33 and the second resistor 34 and the short stub 36 including the third capacitor 35 are connected in parallel, and are connected between the node 50 and the ground terminal. .

  On the other hand, the stabilization circuit in the conventional microwave amplifier circuit corresponds to the stabilization circuit 30 of FIG. 1 that is configured by only the first capacitor 31 and the second resistor 34. That is, in the stabilization circuit in the conventional microwave amplifier circuit, a capacitor (corresponding to the first capacitor 31) is connected between the input side electrode of the FET 20 and the node 50, and a resistor is connected between the node 50 and the ground terminal. (Corresponding to the second resistor 34) is connected.

  Next, the operation of the microwave amplifier circuit 10 of the first embodiment will be described. In the signal input from the input terminal 41, the input impedance of the FET 20 is sufficiently higher than the resistance value of the second resistor 34 in the low frequency region, so that the current of the input signal hardly flows to the FET 20 side. It flows to the second resistor 34. As a result, the circuit loss is increased, so that stabilization can be achieved.

  On the other hand, in the high frequency region, the input impedance of the FET 20 is sufficiently lower than the resistance value of the second resistor 34, so that the current of the input signal hardly flows through the second resistor 34. As a result, almost no circuit loss occurs in the second resistor 34, so that the gain does not deteriorate at a desired frequency (high frequency region).

  In the stabilization circuit 30 according to the first embodiment, a first resistor 32 is further connected in parallel to the first capacitor 31. By adopting such a configuration, the bias can be supplied to the FET 20 through the first resistor 32. Therefore, the bias supply line can be loaded anywhere between the input terminal 41 and the FET 20, and the bias circuit can be designed. The degree of freedom can be increased.

  Further, the input impedance Z1 of the microwave amplifier circuit 10 can be increased by the action of the short stub 36 having the third capacitor 35. As a result, impedance transformation is facilitated, and a plurality of microwave amplifier circuits can be easily connected in parallel. Further, the input impedance Z1 can be increased by the action of the short stub 36, and the impedance transformation is facilitated, so that the microwave amplifying circuit 10 can be widened.

  Next, specific characteristics of the stabilization circuit 30 in FIG. 1 will be described using calculation examples. The frequency used was f = 34 GHz. Further, it is assumed that the input impedance and the stability coefficient K of the microwave amplifier circuit 10 in FIG. 1 are calculated in the frequency band of 1 to 40 GHz. FIG. 2 is a Smith chart showing changes in input impedance in the microwave amplifying circuit 10 according to the first embodiment of the present invention. FIG. 3 is a diagram showing the frequency characteristic of the stability coefficient in the microwave amplifying circuit 10 according to the first embodiment of the present invention. 2 and 3 both show the characteristics of a microwave amplifier circuit having a conventional stabilization circuit for comparison. In FIG. 2, a square (□) indicates the input impedance of the microwave amplifier circuit 10 according to the first embodiment of the present invention, and a triangle (Δ) indicates the input impedance of the microwave amplifier circuit having the conventional stabilization circuit. In FIG. 3, a square (□) indicates an input stability coefficient of the microwave amplifier circuit 10 according to the first embodiment of the present invention, and a triangle (Δ) indicates a stability coefficient of a microwave amplifier circuit having a conventional stabilization circuit.

In this calculation, the circuit constants in the stabilization circuit 30 are as follows.
First capacitor 31 = 0.7 pF
First resistor 32 = 500Ω
Second capacitor 33 = 100 pF
Second resistance 34 = 100Ω
Third capacitor 35 = 3 pF

The circuit constants corresponding to the first capacitor 31 and the second resistor 34 in the conventional stabilization circuit are as follows.
Capacitor = 3pF
Resistance = 200Ω

  As shown in FIG. 2, by applying the stabilization circuit 30 of the first embodiment, the input impedance is higher in the vicinity of the use frequency f = 34 GHz than the conventional stabilization circuit. I understand.

  Further, from FIG. 3, even when the stabilization circuit 30 of the first embodiment is applied, the same characteristics can be obtained in the used frequency region as in the case of applying the conventional stabilization circuit, and the entire frequency region can be obtained. Thus, the FET can be stabilized.

  According to the first embodiment, the stabilization circuit in the microwave amplifier circuit includes a configuration in which the second resistor is further connected in parallel to the first capacitor, whereby the bias circuit can be freely arranged, and the bias circuit The degree of freedom in circuit design can be increased. Furthermore, by using a short stub, the input impedance of the microwave amplifier circuit can be increased and impedance transformation can be facilitated. Thereby, it is possible to realize a wide band of the microwave amplifier circuit.

Embodiment 2. FIG.
FIG. 4 is a circuit configuration diagram of the microwave amplifier circuit according to the second embodiment of the present invention. Compared with the microwave amplifier circuit 10 of the first embodiment in FIG. 1, the microwave amplifier circuit 10a of the second embodiment in FIG. 4 has a fourth capacitor 37 and a third resistor in the stabilization circuit 30a. The other configurations are the same except that 38 is provided.

  Here, the fourth capacitor 37 and the third resistor 38 are connected in parallel to constitute a third circuit. The third circuit having the fourth capacitor 37 and the third resistor 38 is connected between the input terminal 41 and the node 50.

  Next, the operation of the microwave amplifier circuit 10a according to the second embodiment will be described. The microwave amplifier circuit 10a according to the second embodiment has the following two advantages as in the first embodiment. The first is an advantage that the bias supply line can be freely arranged between the input terminal 41 and the FET 20, and the second is that the input impedance of the microwave amplifying circuit 10a is increased by using the short stub 36, and the impedance is improved. This is an advantage that transformation can be easily performed.

  Furthermore, the microwave amplifying circuit 10a of the second embodiment has the following advantages by including the third circuit including the fourth capacitor 37 and the third resistor 38. In the low frequency region, since the impedance of the fourth capacitor 37 is sufficiently larger than the resistance value of the third resistor 38, the current of the input signal flows through the third resistor 38, and the circuit loss increases. Therefore, compared with the conventional stabilization circuit or the stabilization circuit 30 of the first embodiment, the stabilization circuit 30a of the second embodiment can further stabilize in the low frequency region and suppress oscillation. it can.

  Next, specific characteristics of the stabilization circuit 30a in FIG. 4 will be described using calculation examples. As in the case of the first embodiment, the operating frequency is set to around f = 34 GHz. Further, it is assumed that the gain MAG and the stability coefficient K of the microwave amplifying circuit 10a in FIG. 2 are calculated in a frequency band of 1 to 40 GHz. FIG. 5 is a diagram showing frequency characteristics of gain in the microwave amplifying circuit 10a according to the second embodiment of the present invention. FIG. 6 is a diagram showing the frequency characteristic of the stability coefficient in the microwave amplifier circuit 10a according to the second embodiment of the present invention. 5 and 6 both show the characteristics of a microwave amplifier circuit having a conventional stabilization circuit for comparison.

In this calculation, the circuit constants in the stabilization circuit 30a are as follows.
First capacitor 31 = 0.7 pF
First resistor 32 = 500Ω
Second capacitor 33 = 100 pF
Second resistance 34 = 100Ω
Third capacitor 35 = 3 pF
Fourth capacitor 37 = 0.7 pF
Third resistor 38 = 500Ω

The circuit constants corresponding to the first capacitor 31 and the second resistor 34 in the conventional stabilization circuit are as follows.
Capacitor = 3pF
Resistance = 200Ω

  As shown in FIG. 5, by applying the stabilization circuit 30a of the second embodiment, it is possible to reduce the gain MAG at frequencies other than the range of the used frequency, compared with the conventional microwave amplifier circuit. , More stable.

  Further, from FIG. 6, even when the stabilization circuit 30a of the second embodiment is applied, it is equivalent in the use frequency region as in the case where the conventional stabilization circuit or the stabilization circuit 30 of the first embodiment is applied. Thus, the FET can be stabilized in the entire frequency range.

  According to the second embodiment, the fourth capacitor and the third resistor are newly provided as a stabilization circuit in the microwave amplifier circuit, so that the same effect as in the first embodiment can be obtained and the low frequency can be obtained. In the region, it is possible to realize a microwave amplifier circuit that is further stabilized and suppresses oscillation.

Embodiment 3 FIG.
FIG. 7 is a circuit configuration diagram of the microwave amplifier circuit according to the third embodiment of the present invention. Compared with the microwave amplifier circuit 10 of the first embodiment in FIG. 1, the microwave amplifier circuit 10 b of the third embodiment in FIG. 7 is a second circuit having a second capacitor 33 and a second resistor 34. The position of the node 50 indicating the connection point is different, and the other configurations are the same.

  Next, the operation of the microwave amplifier circuit 10b according to the third embodiment will be described. The microwave amplifier circuit 10b according to the third embodiment has the following two advantages as in the first embodiment. The first is an advantage that the bias supply line can be freely arranged between the input terminal 41 and the FET 20, and the second is that the input impedance of the microwave amplifying circuit 10b is increased by using the short stub 36, and the impedance is improved. This is an advantage that transformation can be easily performed.

  Further, the microwave amplifying circuit 10b according to the third embodiment is integrated with the short stub 36 including the third capacitor 35 by changing the connection point of the second circuit having the second capacitor 33 and the second resistor 34. Therefore, the electromagnetic field interference between the second circuit and the short stub can be reduced as compared with the first and second embodiments.

It is a circuit block diagram of the microwave amplifier circuit in Embodiment 1 of this invention. It is a Smith chart which shows the change of the input impedance in the microwave amplifier circuit of Embodiment 1 of this invention. It is a figure which shows the frequency characteristic of the stability coefficient in the microwave amplifier circuit of Embodiment 1 of this invention. It is a circuit block diagram of the microwave amplifier circuit in Embodiment 2 of this invention. It is a figure which shows the frequency characteristic of the gain in the microwave amplifier circuit of Embodiment 2 of this invention. It is a figure which shows the frequency characteristic of the stability coefficient in the microwave amplifier circuit of Embodiment 2 of this invention. It is a circuit block diagram of the microwave amplifier circuit in Embodiment 3 of this invention.

Explanation of symbols

  10, 10a Microwave amplifier circuit, 20 FET (transistor), 30, 30a Stabilization circuit, 31 First capacitor, 32 First resistor, 33 Second capacitor, 34 Second resistor, 35 Third capacitor , 36 short stub, 37 fourth capacitor, 38 third resistor, 41 input terminal, 42 output terminal.

Claims (3)

In a microwave amplifier circuit in which a stabilization circuit and a transistor are connected in series in the signal path from the input terminal to the output terminal,
The stabilization circuit includes a first circuit in which a first resistor and a first capacitor are connected in parallel, and a second circuit in which a second resistor and a second capacitor having one end grounded are connected in series. A circuit and a short stub having a third capacitor;
The first circuit is connected in series between the input terminal and the input electrode of the transistor, and the second circuit and the short stub are connected in parallel between the input terminal and the first circuit. A microwave amplifier circuit characterized by that. The microwave amplifier circuit according to claim 1,
A microwave amplifier circuit, wherein a circuit in which a fourth capacitor and a third resistor are connected in parallel is connected in series between the stabilization circuit and the input terminal. In a microwave amplifier circuit in which a stabilization circuit and a transistor are connected in series in the signal path from the input terminal to the output terminal,
The stabilization circuit includes a first circuit in which a first resistor and a first capacitor are connected in parallel, and a second resistor in which a second resistor and a second capacitor having one end grounded are connected in series. A circuit and a short stub having a third capacitor;
The first circuit is connected in series between the input terminal and the input electrode of the transistor, the short stub is connected in parallel between the input terminal and the first circuit, and the third capacitor is connected to the third capacitor. A microwave amplifier circuit, wherein the second circuit is connected in parallel.

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