JPH0575357A - Low noise amplifier - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a low noise amplifier capable of optimally matching the noise of the FET portion when the frequency band used is changed. A variable frequency band matching circuit 19 including a microstrip line 10 and a variable capacitance diode 14 connected in series between a source electrode of an FET 9 and a ground, and an RF choke coil 15 connected in parallel with the microstrip line 10 is provided. Therefore, the impedance of the variable frequency band matching circuit 19 can be changed when the frequency band used is changed, and F
Optimal matching of ET9 noise can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low noise amplifier for amplifying an input microwave signal, and in particular, it makes variable matching of an electric field effect transistor (hereinafter referred to as FET) to an optimum power source impedance and also a used frequency band. The present invention relates to a low-noise amplifier that operates.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional combination circuit of a matching circuit in which a microstrip line is connected between a source electrode of an FET and ground and a matching circuit including a stub in which a microstrip line and a variable capacitor are connected in series. FIG. 1 is an equivalent circuit diagram showing a low noise amplifier, in which 6 is a microstrip line, 7 is a variable capacitor connected in series to the microstrip line 6, 8 is a variable frequency band matching circuit on the input side including these, 13 Is a variable frequency band matching circuit on the output side having the same configuration. Reference numeral 9 is an FET for amplifying the input microwave signal, and 10 is a microstrip line connected between the source electrode of the FET 9 and the ground. FIG. 3 is a Smith chart diagram in which the frequency characteristics of the optimum power source impedance and the input impedance of the FET are simulated at 8 to 12 GHz.

Next, the operation will be described. If the microstrip line 10 is connected between the source electrode of the FET 9 and the ground, F
When the variable frequency band matching circuit 8 on the input side is designed so that the input impedance of the ET9 and the optimum power supply impedance are close to each other and the noise figure is minimized, the source electrode of the FET9 is directly grounded. In some cases, the reflection on the input side can be reduced. However, if the frequency is deviated from the frequency used as shown in FIG. 3, the input impedance and the optimum power source impedance are separated from each other.

Further, there is an optimum matching point for gain as well as an optimum power source impedance for noise figure. In designing a multi-stage low noise amplifier, it is the noise figure of the first stage amplifier that determines the noise characteristic, and by performing gain matching after the second stage, a low noise and high gain amplifier can be realized.

Since the variable frequency matching circuit 8 on the input side is adapted to match the input impedance of the FET 9 with respect to the changed frequency, it deviates from the optimum matching point and optimum power source impedance with respect to noise and gain. ..

[0006]

Since the conventional low noise amplifier is constructed as described above, optimum noise matching is performed with respect to the frequency used, and when multistage or multiple frequencies are used. When used, there is a problem in that it is necessary to optimize the microstrip line between the source electrode of the FET and the ground plane.

The present invention has been made to solve the above-mentioned problems, and it is possible to bring the input impedance of the FET and the optimum matching point of the gain close to each other at the same frequency, and when the frequency is changed. Also FET
By making it possible to approach the input impedance of, the optimum power source impedance, and the gain matching point, respectively,
It is an object of the present invention to obtain a low noise amplifier which enables variable frequency in the same circuit and adjustment to noise matching and gain matching at that frequency.

[0008]

SUMMARY OF THE INVENTION A low noise amplifier according to the present invention provides a variable frequency band matching circuit with a set value of a variable capacitance connected in series to a microstrip line connected between a source electrode of an FET and ground. The impedance is changed.

[0009]

According to the present invention, the impedance of the variable frequency band matching circuit is changed according to the set value of the variable capacitance connected in series to the microstrip line connected between the source electrode of the FET and the ground, and the optimum power source impedance and the input are obtained. It can be close to the impedance.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a block configuration of a low noise amplifier according to an embodiment of the present invention, in which 14 is an FET.
A variable capacitance diode connected in series to the microstrip line 10 connected between the source electrode of 9 and the ground, and 15 connected in parallel to these, for flowing a direct current between the source and the ground. RF choke coil, 16
Is the bias terminal of the diode.

Further, FIG. 3 shows a microstrip line 10 and a variable capacitor 1 between the source electrode of the conventional FET 9 and the ground.
It is a Smith chart figure which compared on the simulation the frequency characteristic of the optimal power source impedance and input impedance in case of connecting 4 in series at 8-12 GHz.

Next, the operation will be described. In the variable frequency band matching circuit 19 in which the variable capacitance diode 14 is connected in series to the microstrip line 10, when the voltage is applied to the bias terminal 10 and the capacitance value of the diode 14 is changed, the impedance of the variable frequency band matching circuit 19 changes. To do. With this capacitance setting value, when the variable frequency band matching circuit 19 is connected between the source electrode of the FET 9 and the ground, the optimum power source impedance and the input impedance can be brought close to each other even if the frequency band used changes. is there.

For example, as shown in FIG. 3, when the conventional capacitance values are set to 0.5 pF and 1 pF, both are 11 GHz when the capacitance value is 0.5 pF and 10 GHz when the capacitance value is 1 pF. The impedance is closest.

FIG. 2 is a diagram showing a block configuration of a low noise amplifier according to another embodiment of the present invention. In FIG.
Reference numeral 7 is an FET used as a variable capacitor, and 18 is a bias terminal of the FET 17.

Next, the operation will be described. In the variable frequency band matching circuit 19a in which the variable capacitance FET 17 is connected in series to the microstrip line 10, when a voltage is applied to the bias terminal 10 and the capacitance value of the diode 14 is changed, the impedance of the variable frequency band matching circuit 19a changes. .. With this capacitance setting value, when the variable frequency band matching circuit 19a is connected between the source electrode of the FET 9 and the ground, the optimum power source impedance and the input impedance can be brought close to each other even if the frequency band used changes. is there.

In these two embodiments, the FET 9
Microstrip line 1 between the source electrode and ground
0 and the variable capacitance diode 14, or the microstrip line 10 and the FET 17 are connected in series, and the RF choke coil 15 is connected in parallel to them, so that the variable frequency band matching circuit 19 can be used even if the used frequency band changes.
The impedance of can be changed, and the optimum power source impedance and the input impedance can be brought close to each other.

In the above-mentioned embodiment, the microstrip line 10 is used as an example of the line connected to the variable capacitor, but a coplanar line may be used, and the same effect as that of the above-mentioned embodiment can be obtained.

[0018]

As described above, according to the low noise amplifier of the present invention, the variable frequency band can be changed by the set value of the variable capacitance connected in series to the microstrip line connected between the source electrode of the FET and the ground. Since the impedance of the matching circuit is changed, the FE does not change even if the frequency is changed.
It is possible to bring the optimum power source impedance of T and the input impedance close to each other. Therefore, when changing the frequency band used, it is possible to make the input side and the output side match after making it easy to make the match, and change the frequency. Even if this is done, there is an effect that a low noise amplifier with optimized characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram showing an equivalent circuit of a low noise amplifier according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram showing an equivalent circuit of a low noise amplifier according to another embodiment of the present invention.

FIG. 3 is a Smith chart diagram by simulation of the input impedance and the optimum power source impedance of the FET including the series feedback section of the present invention.

FIG. 4 is an equivalent circuit diagram showing an equivalent circuit of a conventional low noise amplifier.

[Explanation of symbols]

1 Input Terminal 2 Microstrip Line Constituting Short Stub 3 Bypass Capacitor 4 Gate Bias Terminal 5 Microstrip Line Constituting Main Line 6 Microstrip Line 7 Variable Capacitance 8 Variable Frequency Band Matching Circuit on Input Side 9 FET 10 Microstrip Line 11 Drain Bias Terminal 12 Output Terminal 13 Variable Frequency Band Matching Circuit on Output Side 14 Variable Capacitance Diode 15 RF Choke Coil 16 Bias Terminal 17 FET 18 Bias Terminal 19 Variable Frequency Band Matching Circuit 19a Variable Frequency Band Matching Circuit

Claims (3)

[Claims] 1. A first variable frequency band matching means provided on an input side, a field effect transistor for amplifying an input microwave signal, and a second variable frequency band matching means provided on an output side. In the low noise amplifier, a third variable frequency band matching having a microstrip line and a variable capacitor connected in series between the source electrode of the field effect transistor and ground, and an RF choke coil connected in parallel with them. A low noise amplifier comprising means. 2. The low noise amplifier according to claim 1, wherein a diode is used as the variable capacitor. 3. The low noise amplifier according to claim 1, wherein the variable capacitor uses a field effect transistor.