JPS61102805A - Linear amplification system - Google Patents

Abstract

PURPOSE:To operate a linear amplifier in an approximately optimum action area by extracting a distortion component and controlling the bias of the linear amplifier so as to minimize said component. CONSTITUTION:An input signal applied to a terminal IN is amplified by the linear amplifier 2 and outputted through a band-pass filter 3. Some part of the amplified signal is applied to a bias control circuit 7 through a low-pass filter 6. Said circuit 7 controls the bias of the linear amplifier 2 so that the output of the low-pass filter 6 can be minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a linear amplification system used, for example, in a vehicle sideband wireless communication system.

Generally, amplifiers used in vehicle sideband wireless communication systems (hereinafter abbreviated as SSB wireless systems) are biased so that they operate in a linear region.

However, if, for example, a semiconductor element is used as this amplifier, the optimum bias will deviate if the ambient temperature, input signal level, etc. change, but the bias is not given with all these conditions strictly taken into consideration.

Rather, even if the above-mentioned bias fluctuations are taken into account, a semiconductor element that is one rank higher in performance is used so that it can still operate in the linear section, but as the operating frequency increases, the amplifier Price becomes expensive.

Therefore, there has been a demand for a linear amplification system that can reduce costs by maximizing the performance of semiconductor devices.

[Conventional technology]

FIG. 4 shows a block diagram of a conventional example.

In the figure, a radio frequency input signal applied to the terminal IN passes through a bandpass filter l, which also operates as a matching section, and is amplified by a linear amplifier 2 using a transistor. The waveform is matched by the wave generator 3 and sent to the outside.

Incidentally, in order to operate the amplifier 2 in a linear region as much as possible even if the ambient temperature changes, a bias is supplied via a temperature compensation circuit.

The illustrated example of this temperature compensation circuit is a circuit using a diode 4, and a circuit 5 including a thermistor 5-1 used in place of this circuit.

Incidentally, when the temperature compensation circuit described above is mounted, it is arranged as close as possible to the transistor part so that the temperature changes between this part and the transistor part are almost equal, thereby ensuring stable operation of the linear amplifier.

[Problem that the invention seeks to solve]

However, in the SSB wireless system, in addition to the temperature change described above, the input level also fluctuates, but compensation for the latter is hardly compensated for.

For this reason, if the generated distortion does not meet the specifications, it is necessary to replace the transistor with a higher performance transistor.

For this reason, there was a problem in that the price of the equipment increased.

[Means for solving problems]

The above problem lies in the linear amplifier whose bias is controlled so that the level of the output wave of the linear amplifier that has passed through a low-pass filter whose cutoff frequency is the transmission frequency width of the linear amplifier is minimized. This problem is solved by the linear amplification method of the present invention, which amplifies the input signal.

[Effect]

The present invention controls the bias of the linear amplifier so that the level of the output wave of the linear amplifier through a low-pass filter having a cutoff frequency equal to the transmission bandwidth of the linear amplifier is minimized.

By performing such control, deviations from the optimum bias point caused by changes in ambient temperature or fluctuations in input level can be compensated for all at once.

Therefore, the capability of the linear amplifier can be maximized, so there is no need to consider a large margin, and the cost of the equipment can be reduced.

〔Example〕

When the unnecessary waves generated by the distortion components of the linear amplifier are calculated for the case of two desired waves Fa and Fb, various distortion components as shown in FIG. 3 are generated.

For example, 2Fa-Fb=Fc″, 2Fb-Fa=Fc
Fa - Fb = Fd, etc. Here, if Fa and Fb are the lower and upper limits of the transmission bandwidth, Fd is the cutoff frequency of a low-pass filter that filters the output wave of the linear amplifier.

The difference component between two waves with arbitrary frequencies between Fa and Fb has a frequency lower than Fd, so Fa and F
All components between b and b pass through a low-pass filter.

Furthermore, since there is a strong correlation between Fc and Pc' and the generation of Fd, Fc and Fc' can also be reduced by controlling the bias of the linear amplifier so as to minimize the Fd component.

FIG. 1 shows a block diagram of one embodiment of the invention.

Note that the same reference numerals indicate the same objects throughout the figures.

In the figure, an input signal applied to a terminal IN is amplified by a linear amplifier 2 and outputted via a bandpass filter 3.

On the other hand, a part of the amplified signal passes through the low-pass filter 6 and is applied to the bias control circuit 7, but this circuit 7 is designed so that the output of the low-pass filter 6 is minimized. Controls the bias of linear amplifier 2.

FIG. 2 is a block diagram of one embodiment of the bias control circuit shown in FIG. 1.

The operation of this circuit is as follows.

First, the output from the low-pass filter 6 is rectified by the rectifier 8, and the rectified output is sampled by the sampling circuit 9 and then written to the memory.

In the comparator 11, the previous value written in the memory 10 and
When the current value is compared with the current value and the current value becomes higher (that is, the distortion becomes worse), the value of the counter 12 is increased from the previous value.

The value of this counter is converted into a negative increased analog quantity by the digital/analog converter 13 and then superimposed on the positive bias power supply 15, so that the bias of the linear amplifier 2 becomes shallow.

Conversely, as the distortion decreases, the bias becomes deeper.

Note that bias control is performed discontinuously.

〔Effect of the invention〕

As described in detail above, the present invention extracts distortion components and controls the bias of the linear amplifier so as to minimize them, so that the linear amplifier can be operated in a substantially optimal operating region.

For this reason, there is no need to provide extra margin in terms of performance as a linear amplifier, which has the effect of reducing costs.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of a bias control circuit, FIG. 3 is a distortion generation diagram, and FIG. 4 is a block diagram of a conventional example. In the figure, 1.3 is a bandpass filter, 2 is a linear amplifier, 6 is a low-pass filter, and 7 is a bias control circuit. Kaya 1 Figure Kaya 2 Kuni

Claims (1)

[Claims] The input signal is amplified by the linear amplifier whose bias is controlled so that the level of the output wave of the linear amplifier that has passed through a low-pass filter whose cutoff frequency is the transmission bandwidth of the linear amplifier is minimized. A linear amplification method that is characterized by