JPH04296108A - Nonlinear distortion compensation device - Google Patents

Abstract

PURPOSE:To implement nonlinear distortion compensation with high accuracy by providing an envelope circuit so as to obtain a same as or similar to an envelope of an IF signal as an input signal of the nonlinear distortion compensation control circuit. CONSTITUTION:The device is provided with a modulator 11, a nonlinear distortion compensation control circuit 12 and an envelope circuit 13. The modulator 11 is an amplitude modulator or a phase modulator. Then the envelope circuit 13 generates an envelope signal the same as or similar to the envelope of an IF signal (subject to residual side band modulation by a video signal) inputted to the modulator 11 from the inputted video signal. Moreover, the nonlinear distortion compensation control circuit 12 generates a control signal in response to a level of the envelope signal inputted from the envelope circuit 13 and outputs it to the modulator 11. The modulator 11 modulates the IF signal inputted according to the control signal. Thus, the nonlinear distortion of the IF signal subject to residual side band modulation is compensated with high accuracy.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linear distortion compensation circuit, and more particularly to a pre-compensation circuit for non-linear distortion of a television signal modulated with residual sidebands by a video signal.

0002

2. Description of the Related Art A conventional nonlinear distortion compensation circuit includes a modulator 41 and a nonlinear distortion compensation control circuit 42 for controlling the modulator 41, as shown in FIG. Modulator 41 is an amplitude modulator or a phase modulator. Nonlinear distortion compensation control circuit 4
A video signal is input to 2, and a nonlinear distortion compensation control circuit 4
2 generates a control signal according to the video signal and transmits it to the modulator 4.
Output to 1. The modulator 41 includes a nonlinear distortion compensation control circuit 4
According to the control signal input from 2, modulation is performed to compensate for nonlinear distortion of the IF signal subjected to residual sideband modulation by the video signal.

0003

Generally speaking, nonlinear distortion changes depending on the peak value of a signal, that is, the value of the envelope of the signal. Therefore, if the envelope of the signal input to the modulator and the signal input to the nonlinear distortion compensation control circuit are the same or similar, it becomes possible to compensate for nonlinear distortion with high accuracy. However, in the conventional nonlinear distortion compensation device, since the IF signal to be compensated is a residual sideband modulated IF signal, the envelope of this IF signal and the video signal that is the input of the nonlinear distortion compensation control circuit are not the same or similar. For this reason, there is a problem in that the conventional nonlinear distortion compensator cannot accurately compensate for the nonlinear distortion of the IF signal subjected to residual sideband modulation. SUMMARY OF THE INVENTION An object of the present invention is to provide a nonlinear distortion compensation device that can accurately compensate for nonlinear distortion of an IF signal subjected to residual sideband modulation.

0004

According to the present invention, there is provided a non-linear distortion compensation control circuit which receives a video signal and generates a control signal based on the video signal; A nonlinear distortion compensation device comprising: a modulator to which the IF signal and the control signal are input, and which compensates for the nonlinear distortion of the IF signal according to the control signal;
An envelope circuit for determining an envelope of the video signal and outputting an envelope signal is provided before the non-linear compensation control circuit, and the non-linear distortion compensation control circuit generates the control signal based on the envelope signal. A nonlinear distortion compensator characterized by the following is obtained. Further, the IF signal is input to the envelope circuit instead of the video signal, and an envelope signal representing the envelope of the IF signal is output to the nonlinear distortion compensation control circuit. A nonlinear distortion compensator is obtained.

[0005]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment of the invention. The nonlinear distortion compensation device of this embodiment includes a modulator 11, a nonlinear distortion compensation control circuit 12, and an envelope circuit 13. As before, modulator 11 is an amplitude modulator or a phase modulator. The envelope circuit 13 creates and outputs an envelope signal that is the same as or similar to the envelope of the IF signal (residual sideband modulated by the video signal) input to the modulator 11 from the input video signal. do. The nonlinear distortion compensation control circuit 12 generates a control signal according to the level of the envelope signal input from the envelope circuit 13 and outputs it to the modulator 11 . Modulator 11
modulates the input IF signal according to the control signal.

Next, the operation will be explained using diagrams and mathematical formulas. Here, a video signal having a time waveform and spectrum as shown in FIG. 5 will be considered as an example. Note that the relationship between the time waveform and spectrum in FIG. 5 is not strict. Also, the spectrum represents only positive frequency components.

When the video signal shown in FIG. 5 is subjected to amplitude modulation of the carrier wave of frequency fo and is further passed through the vestigial sideband modulation filter shown in FIG. 6, the vestigial sideband modulation IF shown in FIG. 7 is obtained.
I get a signal. The residual sideband modulation IF thus obtained
The signal is input to a modulator 11 and the video signal is input to an envelope circuit 13. By the way, as shown in the spectrum diagram of FIG. 7, the residual sideband modulation IF signal has no signal with a frequency component lower than the frequency fo -fa. Therefore, when comparing the time waveform envelope of the residual sideband modulation IF signal (shown in Figure 7) and the time waveform of the video signal (shown in Figure 5), it is found that the signals in the frequency range lower than fa are almost one pair. 1
On the other hand, the amplitude of signals in a frequency range higher than fa is approximately 1:2. (Time waveform in Figure 5 and Figure 7
In the envelope of the time waveform, the central four sine waves are assumed to be signals in a frequency range higher than fa, and the others are signals in a frequency range lower than fa. )

Therefore, the purpose of the envelope circuit 13 is to create a waveform identical to the envelope of the residual sideband modulation IF signal from the video signal. For example, if a filter circuit as shown in FIG. 8 is used, the video signal in FIG. 5 can be converted into a signal having a time waveform and spectrum as shown in FIG. 9. Further, the characteristics of the envelope circuit can be expressed using the following formula.

Env(t) = [{F- (t) *V(t
) }・{F+ (t) *V(t) }]1/2 Env(t) : Envelope circuit output signal (variable t is expansion) V(t) : Input video signal F+ (t) ,F- ( t): Impulse response of frequency characteristics derived from the residual sideband filter. *: Represents convolution.

The impulse response VSB(t) of the frequency characteristic of the vestigial sideband filter is F+ (t), F- (t)
Using , it can be expressed as the following equation. VSB(t) =F+ (t) ・ej2πfot +
F- (t) j2πfot fo : Center frequency of the filter for vestigial sideband modulation Note that the first term is the impulse response of the positive frequency characteristic of the filter for vestigial sideband modulation, and the second term is the impulse response of the negative frequency characteristic of the filter for vestigial sideband modulation. It is an impulse response. Also, . represents multiplication.

The envelope signal which is the output of the envelope circuit 13 thus obtained is input to the nonlinear distortion compensation control circuit 12. The nonlinear distortion compensation control circuit 12 sends an appropriate compensation control signal to the modulator 1 according to the level of the input envelope signal.
Output to 1. The modulator 11 performs amplitude or phase modulation on the input IF signal according to the value of the input control signal, and outputs an IF signal compensated for nonlinear distortion.

FIG. 2 shows a second embodiment. This embodiment includes an envelope circuit 21 that extracts and outputs an envelope signal representing the envelope of an IF signal subjected to residual sideband modulation. The modulator 11 and the nonlinear distortion compensation control circuit 12 are the same as in the first embodiment. Further, the operation thereof is the same except that the envelope circuit 21 extracts the envelope signal from the IF signal, so a description thereof will be omitted.

FIG. 3 shows a third embodiment. The nonlinear distortion compensation device of this embodiment includes an amplitude modulator 31, a phase modulator 32,
It has an amplitude nonlinear distortion compensation control circuit 33, a phase nonlinear distortion compensation control circuit 34, and an envelope circuit 13. The nonlinear distortion compensation devices of the first and second embodiments are devices that perform nonlinear distortion compensation for either amplitude or phase. In contrast, the nonlinear distortion compensator of this embodiment can simultaneously perform amplitude and phase nonlinear distortion compensation. Note that the explanation of the operation will be omitted.

Note that the present invention can be similarly implemented in a circuit that handles signals in analog form or as digital codes. Furthermore, it is also possible to insert a delay circuit and a phase circuit in each input as necessary to match the delay time or phase of the residual sideband modulated IF signal and the video signal.

[0015]

Effects of the Invention As explained above, the nonlinear distortion compensation circuit of the present invention uses the IF
By providing the envelope circuit so as to obtain a signal that is the same as or similar to the envelope of the signal, nonlinear distortion compensation can be performed with high precision.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a first embodiment of the invention.

FIG. 2 is a block diagram of a second embodiment of the invention.

FIG. 3 is a block diagram of a third embodiment of the invention.

FIG. 4 is a block diagram of a conventional nonlinear distortion compensation device.

FIG. 5 is a time waveform and spectrum of a video signal.

FIG. 6 shows positive frequency characteristics of a vestigial sideband modulation filter.

FIG. 7 is a time waveform and spectrum of a residual sideband modulated IF signal.

FIG. 8 is an example of positive frequency characteristics of an envelope circuit.

FIG. 9 shows the time waveform and spectrum of the output signal of the envelope circuit.

[Explanation of symbols]

11 Modulator 12 Nonlinear distortion compensation control circuit 13
Envelope circuit 21 Envelope circuit 31 Amplitude modulator 32 Phase modulator

Claims (2)

[Claims] 1. A nonlinear distortion compensation control circuit that receives a video signal and generates a control signal based on the video signal, and an IF signal subjected to vestigial sideband modulation by the video signal and the control signal. and a modulator that compensates for nonlinear distortion of the IF signal according to the control signal, in which an envelope of the video signal is determined and an envelope signal is obtained before the nonlinear compensation control circuit. 1. A nonlinear distortion compensating device, comprising: an envelope circuit for outputting an output, and wherein the nonlinear distortion compensation control circuit generates the control signal based on the envelope signal. 2. The IF signal is input to the envelope circuit instead of the video signal, and an envelope signal representing an envelope of the IF signal is output to the nonlinear distortion compensation control circuit. The nonlinear distortion compensator according to claim 1, characterized in that: