JPH02243005A - Bias device for power amplifier - Google Patents

Abstract

PURPOSE:To improve the power utilizing rate and the efficiency of an output range by correcting a characteristic having a nonlinear area linearly with a bias voltage. CONSTITUTION:A control signal corresponding to a period T of a VHF signal is inputted to a strobe generator 16, from which split pulses AE, AH, AL are outputted and fed respectively to voltage generators 17-19. The output voltage from the voltage generators 17-19 is selected and outputted for each of periods t1-t3 by a multiplexer 20 and fed to a power amplifier 12 as a gate voltage. Thus, the amplification characteristic of a MOS-FET in the inside of the power amplifier 12 is corrected relatively linearly.

Description

DETAILED DESCRIPTION OF THE INVENTION CObject of the Invention] (Industrial Application Field) The present invention relates to a bias device for a high frequency amplifier used in a high frequency power amplification device.

(Prior Art) Conventionally, vacuum tubes have been mainly used as amplification elements in high-output power amplifiers of several hundred volts or more.

However, recently, with the advancement of semiconductor technology, MOS-
A 100W-(i00ν class discrete element amplifier using PET has been developed.

FIG. 4(a) is an example in which the above amplifier is used to amplify intermittent high frequencies in the VHF band.

A VHF band signal source 1 is connected to an input end of a function generator 2 . V from function generator 2
The HF signal is supplied to the power amplifier 3 and amplified. Furthermore, a bias timing pulse is output from the function generator 2 in synchronization with the output period of the VHF signal, and is supplied to the bias power supply circuit 4. Thereby, the bias power supply circuit 4 controls the gate voltage of the amplification element of the power amplifier 3.

Here, the VHF signal is AM-modulated into a triangular waveform (see FIG. 6(b)). Therefore, in the power amplifier 4, a bias voltage is applied in synchronization with the intermittently arriving triangular AM waves to reduce power consumption. Fields that handle high frequencies that arrive in the form of impulses or pulses include, for example, laser processing equipment and nuclear magnetic resonance imaging equipment.

(Problem to be Solved by the Invention) By the way, when a semiconductor element such as a MOS-FET is used in the above power amplifier, the gate voltage EC and drain current 10 have a relationship as shown in FIG. ,
There is a linear area A1 and non-linear areas A2 and A3. For this reason, when attempting to amplify a triangular AM wave with good linearity, a sufficient range cannot be obtained because the usable area is limited. Also, to layer only the straight a area.

There are problems such as poor power usage efficiency.

SUMMARY OF THE INVENTION An object of the present invention is to provide a bias device for a power amplifier that has a good power utilization rate and can efficiently improve the output range.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a high-frequency amplifier to which a high-frequency signal that has been AM-modulated into a triangular wave is intermittently manually input, and a gain control device for a semiconductor amplification element of the high-frequency amplifier. In a bias device for a power amplifier comprising a bias circuit that provides a gate bias voltage for setting, an area where the level of the triangular wave is low is synchronized with the high frequency signal being manually input to the high frequency amplifier.

In the intermediate region and the high region, the output voltage waveform of the bias circuit is nonlinear in the direction of increasing the gain, respectively.
It is provided with means for varying the waveform into a linear waveform to give the gain a linear characteristic and a nonlinear waveform in the direction of suppressing the gain.

(effect) By the above means, a property with a non-linear region.

The shape is relatively more linearly corrected by the bias voltage, and the amplification region of the amplification element can be used efficiently.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which an input terminal 11 is intermittently supplied with a VHF signal. This VHF signal is
AM modulated in the form of a triangular wave.

This VHF signal is input to the power amplifier 12, amplified according to the gate voltage level, and output to the output terminal 13.

On the other hand, a control signal corresponding to section T of the VHF signal is input to the input terminal 15 (see FIG. 2). This control signal is input to the strobe generator 16. The strobe generator 16 outputs divided pulses (strobe signals) AN, AH, and AL that divide the section of the VHFI signal. The strobe signals AN, AH, and AL are supplied to voltage generators 17, 18, and 19, respectively. Here, the voltage generator 17 generates a voltage with a flat waveform as a strobe signal AN.
The voltage generators 18 and 19 output voltages with nonlinear waveforms during the period of the strobe signal AH. However, the output waveforms of the voltage generators 18 and 19 have slopes in opposite directions.

The output voltage of each voltage generator 17, 18, 19 is changed by a multiplexer 20 for each period tl, t2 . t3
is selected and outputted, and supplied to the power amplifier 12 as a gate voltage. As a result, during the period when the level of the VHF signal is low, the output voltage of the voltage generator 19 is used as the gate voltage, and during the period when the level is intermediate, the output voltage of the voltage generator 17 is used as the gate voltage, and the level is During the high period, the output voltage of the voltage generator 18 is used as the gate voltage. As a result, the amplification characteristics of the MOS-PET inside the power amplifier 12 shown in FIG. 3 are relatively linearly corrected.

[Effects of the Invention] As described above, according to the present invention, the power utilization rate is high;
A bias device for a power amplifier that can efficiently improve the output range can be obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a timing chart shown to explain the operation of the circuit shown in Fig. 1, Fig. 3 is a characteristic diagram of MOS-PET, and Fig. 4 is an explanatory diagram of a conventional power amplifier. 16... Strobe generator, 17.18.19...
Voltage generator, 20... multiplexer, 12... power amplifier. Applicant's agent Patent attorney Takehiko Suzue (a)

Claims (1)

[Claims] A power amplifier comprising a high frequency amplifier to which a triangular AM modulated high frequency signal is intermittently input, and a bias circuit that applies a gate bias voltage for setting the gain to a semiconductor amplification element of the high frequency amplifier. In the bias device, in synchronization with the input of the high frequency signal to the high frequency amplifier, the output voltage waveform of the bias circuit is increased in gain in a low level region, an intermediate region, and a high level region of the triangular wave, respectively. 1. A bias device for a high frequency amplifier, comprising means for varying the waveform to a nonlinear waveform in a direction to suppress the gain, a linear waveform to make the gain a linear characteristic, and a nonlinear waveform in a direction to suppress the gain.