JP3136526B2 - Power amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power amplifier, and more particularly, to a microwave power amplifier for a time division multiple access type transmitter.

[0002]

2. Description of the Related Art In a time division multiple access system, a signal is generally transmitted in a burst only at a certain allocated time.
The ratio of the transmission time of the signal in the repetition period (frame period) is very small, from several to several thousandths. As a transmission power amplifier of such a communication system using microwaves, a traveling wave tube amplifier (TWTA: Travel)
ing Wave Tube Amplifier) and a solid-state power amplifier are used. Since the solid-state power amplifier does not have performance deterioration or life factor and operates at a voltage of 10 V or less, it is easy to maintain, the power supply becomes small and light, and there is a possibility that the power amplifier can be made small. FIG. 5 shows the characteristics of a general high power FET for microwave power amplification. FIG. 1 shows signal output characteristics and power consumption characteristics with respect to a signal input of a general microwave power amplifying high output FET. In the figure, a
Represents output during class A operation, b represents output during class B operation, c represents power consumption during class A operation, and d represents power consumption during class B operation.
One shows the characteristics when the gate bias voltage is selected so that the FET performs class A operation, and the other shows the characteristics when the gate bias voltage is selected so that the FET is pinched off, that is, the case of class B operation. It is. The power consumption c in the case of class A operation is substantially constant irrespective of the signal input, and a large amount of current is consumed even when there is no signal input. The power consumption d in the case of the class B operation is substantially proportional to the signal input, and becomes 0 when there is no input, but the output and the gain are lower than those in the case of the class A operation.

[0003]

The traveling-wave tube amplifier can be expected to have a high output and a high efficiency, but it has a large shape and uses a high voltage, which complicates the power supply.
There is a problem of deterioration of the service life. On the other hand, solid-state power amplifiers use frequencies used for communication, for example, 14 GHz or 30 GHz.
At Hz, solid-state power amplifiers have relatively low output and low efficiency. To obtain high output in a solid-state power amplifier, it is necessary to combine the outputs of many fixed amplification elements, which further reduces the efficiency, increases the amount of heat generated, and significantly increases the size and weight including heat measures. There is a problem of increasing. In the microwave region, harmonic control technology indispensable for class B operation has not yet been established.
In class operation, output and gain are inferior to class A and class AB. Therefore, the operation of the currently used solid-state power amplifier is A
Class A, or Class AB which is intermediate between Class A and Class B. Even when no signal is transmitted, the power amplifier is in operation and consumes power.

FIG. 6 shows a signal transmitted in a burst and an operation state of a conventional solid-state power amplifier. The figure shows the signal (1) transmitted in a burst and the operation state (2) of the solid-state power amplifier in the class A operation. As described above, the ratio of the signal transmission time to the frame period is very small, and most of the consumed power is converted into heat without being emitted as a transmission signal. For this reason, there is a drawback that the power device becomes large in size and weight and expensive in order to generate a large amount of heat and to dissipate equipment for heat radiation and measures against large power. In order to compensate for this drawback, there is a transmission device in which a power amplifier and some additional device such as a power supply control device are provided in parallel to make the power amplifier inactive when no signal is transmitted. However, in order to transmit a signal including a large amount of information at high speed and without loss using the above-described transmission device in an existing communication system, in addition to the transmission device,
For example, the time-division multiplexing device has a new disadvantage that an additional device such as a device for generating an amplifier control signal for turning on / off the FET is required. The present invention has been made in view of the above points, and does not require a special additional device for the burst-like signal shown above, and is small, lightweight, has low power consumption, and is inexpensive for a microwave transmitting device. It is to implement a power amplifier.

[0005]

FIG. 1 is a block diagram showing the principle of the present invention. The present invention has a microwave circuit including a field effect transistor (FET) as an amplifying element, and a bias circuit for supplying power to each of a gate terminal and a drain terminal of the FET, and an input signal is input to the gate terminal. In the power amplifier from which an output signal is taken out from the drain terminal, the voltage at the output terminal of the gate terminal bias circuit of the FET is supplied through a resistor included in the gate terminal bias circuit, and changes according to the level of the input signal power. The FET performs Class B or Class C operation when there is no signal according to the change in the DC impedance at the gate end of the FET.
When the signal is input, the FET operates in Class A or Class AB
A gate end bias circuit including an output voltage varying means for setting the value of the resistor so as to perform the operation.

[0006]

According to the present invention, in a microwave power amplifier using an FET as an amplifying element, an output voltage is supplied to a gate terminal bias circuit of the power amplifier so that power is not consumed when no signal is input and near an FET pinch-off and when a signal is input. By providing an output voltage variable function that changes from (1/4) x (pinch off) to (3/4) x (pinch off) of the FET that provides the desired amplification characteristics, The power consumption is suppressed without using a special additional circuit such as generation of an amplifier control signal, and the both characteristics of the amplifier are not impaired by suppressing the power consumption.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment of the present invention in which a gate bias circuit of a power amplifier has an output voltage variable function, a case where a resistor having a specific high resistance value is provided in a gate bias circuit will be described below with reference to the drawings. It will be described in detail based on this.
FIG. 1 is a schematic diagram of a gate bias circuit of an amplifier using an FET for explaining the operation principle of the present invention. The configuration shown in FIG. 1 includes an FET 1, a constant voltage power supply 2 for gate and bias, a resistor 3, and a constant voltage power supply 4 for drain and bias. Assuming that the resistance value of the resistor 3 is a value R obtained according to a design method described below, as described later, when there is no signal input, the FET 1 is pinched off, the drain current Id is almost 0, and the power consumption is 0. , An amplifier that operates only when a signal input is present. Hereinafter, the principle of the present invention and a method of designing the resistance value R will be described.

[0008] The input impedance of FET1 varies with the gate bias voltage and the input signal level. When a constant voltage power supply is used as the gate bias power supply 2, the change appears as a change in the gate current. Generally, the gate current of the FET in the case of class A and class AB operation is
For example, in the FET 1 of the output 1W class, almost no current flows when there is no signal input, or about several microamps even when the signal is input. However, when the signal input is increased to the extent that the output is saturated, about several milliamps flow. On the other hand, if the gate bias voltage is selected to a value close to the pinch-off voltage of the FET, a gate current of about several tens of microamps to about 1 milliamp flows even when there is no signal input. Gate current flows. FIG.
In the circuit shown in FIG.
Is R, and the gate bias voltage of FET1 is V
g, and the flowing current is Ig. First, the gate direct-current input impedance Zr at the time of operation in which a saturated output of the FET 1 is obtained.
Ask for. The value of Zr can be easily obtained, for example, by measuring the gate-source voltage Vg and the gate current Ig during the actual operation.

Here, if the output voltage V of the gate bias constant voltage power supply 2 is set to a voltage Vp at which the FET 1 is pinched off, the FET 1 does not operate and almost no drain current flows unless there is a signal input. Therefore, no power is consumed. At this time, the gate current Ig flows from several tens of microamps to about 1 milliamp. As the input signal is gradually increased from 0, the input impedance of the FET 1 gradually decreases, and the gate current Ig increases accordingly. For this reason, the voltage drop generated in the resistor 3 gradually increases, and the actual gate bias voltage Vg applied to the FET 1 gradually decreases. When a signal is input so that the amplifier can obtain a saturated output, the gate bias voltage Vg of the FET 1 is utilized by utilizing the voltage drop generated in the resistor 3.
Is a voltage R suitable for a power amplifier, that is, a resistance value R of the resistor 3 which makes the voltage Va at which the FET 1 performs a class A or class AB operation, and the resistance value can be uniquely determined as follows. V = Vp = R · Ig + Va = R · Ig + Zr · Ig = (R + Zr) Ig∴R = (Vp / Va−1) Zr Here, the voltage Va is generally a value of about Vp / 2.
To obtain the resistance value R experimentally, the resistor 3 is a variable resistor, and when there is no signal input while actually operating, Vg
ＶVp, if there is, the variable resistor may be adjusted so that Vg = Va, and the value of R may be measured. At this time, the power Pg consumed by the gate bias circuit is Pg = V · Ig = Vp × (〜several mA) = (〜several mW), and the power Pd = Vd · Id consumed by the drain circuit = (About 10 V) × (several A) = (several tens of W) By setting the resistance value of the resistor 3 to a certain value R obtained in this manner, when there is no signal input, the FET 1 is in a pinch off state, that is, in a non-operating state, the power consumption is suppressed, and ideally, 0. Becomes On the other hand, when there is a signal input,
A class or AB class operation is performed.

FIG. 2 shows the configuration of an embodiment of the present invention. The configuration shown in the figure is a FET 11, an input signal terminal 12, an output signal terminal 13, capacitors 14 to 16, microstrip lines 18 to 23, choke coils 25 and 26, feedthrough capacitors 27 and 28, constant voltage power supplies 29 and 30, matching. It is composed of networks 31, 32 and a resistor 33. Here, the resistor 33 has a specific value determined according to the present invention. Microstrip line 20-23
Has an electrical length of 1/4 or an odd multiple of the wavelength of the used high-frequency signal.

FIG. 3 shows the characteristics obtained by the embodiment of FIG. FIG. 3 shows the input / output characteristics and power consumption of the conventional power amplifier, and the input / output characteristics and power consumption obtained when the present invention is implemented, that is, the power amplifier of the embodiment of FIG. , Output during class A operation, b is output during conventional class B operation, c is power consumption during conventional class A operation, d is power consumption during conventional class B operation, and e is an embodiment of the present invention. And f represents the power consumption of the embodiment of the present invention. As can be seen, the same output and gain as in class A operation can be obtained when a normal RF signal is input, and F and F when no RF signal is input.
ET will automatically pinch off or pinch
The state is almost off, and the power consumption is reduced from a fraction of that of the conventional amplifier to almost zero. The linearity of the input / output characteristics is deteriorated between the above two states, but when outputting a signal with a constant amplitude, the influence of the linearity does not matter.

FIG. 4 shows the operation of the power amplifier in the embodiment of FIG. In the figure, (a) and (b) are the input and output signals of the power amplifier, respectively, and (c) is the drain current of the power amplifier, and the power consumption is almost proportional to the drain current. The time division multiplex signal is composed of a synchronization burst and a data burst. Synchronous burst is about 1 frame interval
In a time division multiple access communication system in which a data burst is transmitted for about one-thousandth or one-thousandth of a frame interval in response to a transmission signal, a power amplifier according to the present invention is used. If applied, the operation of the power amplifier is controlled according to each burst according to the above principle, and the operation and non-operation are switched as shown in the operation state (c), and the power amplifier does not impair the time-division multiplexed signal. Can be amplified. At this time, the FET which is the power amplifying element is on for only about one-thousandth to about one-quarter, and is off for other periods. Therefore, as is apparent from comparison with FIG. 6, the power consumption of the power amplifier is greatly reduced.

[0013]

As described above, according to the present invention, the following effects can be obtained by using the power amplifier according to the present invention when amplifying a burst signal having a constant amplitude. (1) The power consumption of the power amplifier can be significantly reduced, and as a result, the power amplifier can be reduced in size and weight. (2) Since the heat generated by the power amplifier is reduced to half or less, the cooling equipment can be simplified, and the power amplifier can be reduced in size and economical.

[Brief description of the drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a configuration diagram of one embodiment of the present invention.

FIG. 3 is a diagram showing characteristics obtained by the embodiment of FIG. 2;

FIG. 4 is a diagram illustrating an operation of the power amplifier in the embodiment of FIG. 2;

FIG. 5 is a diagram illustrating characteristics of a general microwave power amplifying high-output FET.

FIG. 6 is a diagram showing a signal transmitted in a burst and an operation state of a conventional solid-state power amplifier.

[Explanation of symbols]

 Reference Signs List 1,11 FET (field effect transistor) 2 constant voltage power supply for gate bias 3 resistor 4 constant voltage power supply for drain bias 12 input signal terminal 13 output signal terminal 14-16 capacitor 18-23 microstrip line 25,26 choke coil 27, 28 feed-through capacitor 29, 30 constant voltage power supply 31, 32 matching network 33 resistor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-357705 (JP, A) JP-A 62-103311 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03F 1/00-3/72

Claims (1)

(57) [Claims] 1. A microwave circuit including a field effect transistor (FET) as an amplifying element, and a bias circuit for supplying power to each of a gate terminal and a drain terminal of the FET, and an input signal is input to the gate terminal. And
In the power amplifier from which an output signal is taken out from the drain terminal, the voltage at the output terminal of the gate terminal bias circuit of the FET is supplied through a resistor included in the gate terminal bias circuit, and changes according to the level of the input signal power. FET
The FET performs Class B operation or Class C operation when there is no signal according to the change in the DC impedance at the gate end of
When a signal is input, the FET operates in class A or class AB
A power amplifier having a gate-end bias circuit including an output voltage varying means for setting the value of the resistor so as to perform the following .