JPS6233396Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention mainly relates to a nonlinearity compensation circuit for compensating for cross-modulation components and nonlinear distortion of amplitude and phase caused by nonlinearity of a power amplification stage of a transmitter.

For example, in the case of a television video transmitter, amplitude nonlinearity in the power amplification stage and phase nonlinearity due to AM-PM conversion not only lead to deterioration of differential gain and differential phase, but also require the use of recent IF conversion methods. In such a transmitter, linear amplifiers are connected in cascade in multiple stages after the IF modulator, so the nonlinearity of the amplifiers causes deterioration of the subband wave characteristics and waveform distortion.

Conventionally, in order to compensate for the above-mentioned nonlinear distortion, circuits with characteristics opposite to the nonlinear characteristics of the power amplification stage were installed independently in the preceding stage in terms of amplitude and phase, and predistortion was applied to each. has been taken. However, with this conventional method, in practice, for example, the phase compensation circuit apparently compensates for cross-modulation components (lower band components) caused by amplitude nonlinearity, resulting in unsatisfactory performance such as waveform distortion. The disadvantage is that the adjustment is complicated and difficult.

The present invention aims to eliminate the drawbacks of conventional nonlinearity compensation circuits. Two embodiments of the present invention are shown in the drawings to provide a detailed explanation of the present invention.

The drawing shows an embodiment in which a nonlinearity compensation circuit according to the present invention is inserted into a television video transmitter that employs an IF modulation method. That is, after the video signal input 1 is AM-modulated by the IF video modulator 3 and the IF carrier wave oscillator 2, this modulated wave is passed through a VSB filter and a group delay compensation circuit 4, where it is converted into a video signal having VSB characteristics. A modulated wave can be obtained. The output of this stage has normal amplitude and good phase linearity.

The nonlinearity compensation circuit 5 according to the present invention has this VSB
The filter is inserted after the group delay compensation circuit 4. The input of the nonlinearity compensation circuit 5 is distributed by a distributor 6 to a main line section 8 and a compensation section 19. The signal led to the compensator 19 is divided into two parts by a divider 8, and one signal is passed through a nonlinear amplifier 9 equivalent to the nonlinear characteristic of the power amplifier 16.
After generating a nonlinear distortion equivalent to the nonlinear distortion generated in the power amplifier 16, it is distributed by a distributor 8 and passed through a delay line 10 having the same delay time as that generated in the nonlinear amplifier 9. A difference signal from another linear signal is obtained by a difference circuit 11, adjusted to a required level by a level adjuster 12, and added to a summation circuit 13 inserted in the main line section. The output of the difference circuit 11 becomes a nonlinear distortion signal having a polarity opposite to the nonlinearity characteristic of the power amplifier 16. That is, if the output signal of the nonlinear amplifier is considered to be divided into a linear component and a nonlinear component, the signal appearing here will be only the nonlinear component.

On the other hand, the signal guided to the main line section 18 by the distributor 6 is applied to the summation circuit 13 through the delay line 7 having the same delay time as that occurring in the compensation section. Therefore, the output of the summation circuit 13 is the power amplifier 1
A non-linear distortion opposite to the non-linear distortion occurring in step 6 is added to provide the required amount of compensation. Therefore, this output is transmitted to the frequency converter 14 and the local oscillator 15.
Power amplifier 1 after being converted to the required output frequency by
6, the non-linear distortion generated in the power amplifier 16 is eliminated, and a signal without non-linear distortion is transmitted to the antenna 1.
Fired from 7.

Note that the input circuits of the frequency converter 14 and the power amplifier 16 have a wide band in order to improve cross-modulation components outside the required band such as lower band wave characteristics.

In such a configuration of the present invention, the amount of compensation can be changed by adjusting the level adjustment circuit 12. In this case, only the distortion component added to the signal passing through the summation circuit 13 changes, and the signal level itself of the output of the summation circuit 13 does not change.
Adjustment becomes extremely easy.

As explained in detail in the above embodiments, the present invention consists of a nonlinear amplifier equivalent to a power amplifier that generates nonlinear distortion in a low power stage, and delays the output containing this nonlinear distortion and the linear signal. Synthesize with a time-matched post-difference circuit to obtain a component opposite to the nonlinear distortion of the power amplifier, and combine this with the main line linear signal and delay time to obtain the required amount of nonlinear distortion compensation. This has the advantage of being able to compensate both amplitude nonlinear distortion and phase nonlinear distortion, and adjustment is also very simple.

In this example, the linearity compensation circuit according to the present invention was inserted into the IF stage, but as a matter of course,
It can be configured with the required frequency band of VHF or UHF band.

[Brief explanation of the drawing]

The drawing shows an example in which a nonlinearity compensation circuit according to the present invention is implemented in an IF modulation type television video transmitter. In the figure, 2... IF carrier wave oscillator, 3...
IF video modulator, 4...VSB filter and group delay compensator, 5...nonlinearity compensation circuit,
6, 8...Distributor, 7,10...Delay line, 9...
Nonlinear amplifier, 11... Difference circuit, 12... Level adjustment circuit, 13... Sum circuit, 14... Frequency modulator, 15... Local oscillator, 16... Power amplifier, 17... Antenna, 18... ...Main line section, 19...
...Compensation Department.

Claims (1)

[Scope of utility model registration request] a first divider that divides the signal supplied to the power amplification stage of the transmitter into two; a second divider that divides the first output signal of the first divider into two; and the second divider. a nonlinear circuit that takes the first output signal of the divider as an input and has nonlinear characteristics equal to that of the power amplification stage; and a delay time of the nonlinear circuit that takes the second output signal of the second divider as the input. a first delay line that delays a signal by the amount of the signal, a difference circuit that takes the difference between the output of the nonlinearity circuit and the output of the delay line, and a second output signal of the first divider as input; a second delay line having a delay time equal to the sum of respective delay times of a second divider, the nonlinearity circuit, and the difference circuit; outputs of the difference circuit and the second delay line; 1. A nonlinearity compensation circuit comprising a summation circuit.