JPS609394B2 - Phase modulation distortion correction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention deals with phase modulation distortion, that is, amplitude modulation AM-phase modulation PM conversion (hereinafter referred to as AM-
This invention relates to a phase modulation distortion correction method that automatically reduces PM conversion.

The first AM-PM conversion compensator of the secondary TV relay broadcasting equipment
As shown in the figure. In Fig. 1, 1 is the receiving antenna ANTI,
2 is input filter BPF1, 3 is reception converter RX, 4 is local oscillator for reception conversion LO1, 5 is equalizer EQL, 6 is phase shifter PHSH, 7 is video signal band pass filter FvB
PF, 8 is a video detector DET, 9 is a linearity correction circuit DI
ST, 10 is a transmission conversion unit TX, 11 is a local oscillator for transmission conversion 02, 12 is a power amplifier PA, and 13 is an output terminal. Next, the operation of the AM-PM conversion compensator of the conventional TV relay broadcasting device will be explained based on FIG. First, a predetermined channel is selected from an input signal from a reception antenna 1 by an input filter 2, and converted into an intermediate frequency band (IF band) by a reception conversion section 3 and a reception conversion local oscillator 4. Next, this signal is subjected to equalization of the video signal/audio signal ratio by a brush converter 5, and then enters a phase shifter 6 where it is phase modulated. This phase shift modulation corrects in advance the phase modulation component of AM-PM conversion generated by the amplitude modulated AM video signal when converting and amplifying the signal in the next stage transmission conversion section 10, power amplification section 12, etc. The video signal passes through a passing filter 7 and extracts only the video component, which is further subjected to video detection by a video detector 8, and then sent to a linearity correction circuit 9 by a transmission conversion section 10 and a power amplification section 12. AM that occurs in
-Correct the linearity of the video signal according to the PM conversion characteristics,
It is added to the phase shifter 6 for phase modulation. That is, the audio signal undergoes phase modulation by the amplitude modulated wave (AM wave) of the video signal in the transmission converter 10, power amplifier 12, etc. that generate nonlinear distortion, and this phase modulation rudder M component transfers to the audio signal. This degrades the characteristics of the audio signal, which is a frequency modulated wave (FM wave), and by correcting this AM-PM conversion in advance, a signal with phase modulation distortion corrected is output from the output terminal 13. . However, since this is a feedforward method, if the AM-PM conversion that occurs in the transmission converter 10, power amplifier unit 2, etc. changes,
There was a drawback that the correction characteristics of AM-PM conversion deteriorated.

In order to solve these drawbacks, the present invention automatically compensates for phase modulation distortion using a feedback loop, which will be described in detail below. , 15 is an audio carrier band deceleration filter F^BPF, 16 is a phase detector PHDET, 17 is a local oscillator L03 consisting of a temperature compensated crystal oscillator that can be controlled by voltage, 18 is a mixer MIX, and 19 is an amplifier AMP.
, and the other numbers are the same as in FIG.

The first embodiment of the present invention will be explained below based on FIG.

A predetermined channel of an input signal from a reception antenna 1 is selected by an input filter 2, and converted into an intermediate frequency band (IF band) by a reception conversion section 3 and a reception conversion local oscillator 4. Next, this signal is converted into a video signal/audio signal ratio by an equalizer 5, and then passed through a phase shifter 6 and converted into a predetermined transmission channel by a transmission conversion unit 10 and a transmission conversion local oscillator 11. Thereafter, the signal is amplified by the power amplifying section 12 and output from the output terminal 13. On the other hand, a part of the output signal of the power amplifying section 12 is input to a mixer 18 and converted into an intermediate frequency band (IF band) by a local oscillator 17.

The nominal oscillation frequency of the local oscillator 17 is the same as that of the transmission conversion local oscillator 11, and the frequency can be controlled externally. The output of this mixer 18 passes through an audio carrier band pass filter 15 and enters a phase detector 16 where only the audio signal is selected. Further, a portion of the signal from the equalizer 5 passes through an audio carrier bandpass filter 14 to select only the audio signal, and a phase detector 16 performs phase detection with the output signal of the audio carrier bandpass filter 5. . The output of this phase detector 16 is fed back to the local oscillator 17, which is controlled by the output from the phase detector 16 and is connected to the two audio signals selected by the audio carrier band pass filters 14, 15. Operates so that the phase (frequency) is the same. This audio carrier band pass filter 15,
The first phase-locked loop, which consists of the phase detector 16, local oscillator 17, and mixer 18, feeds back only the low-frequency signal of the phase difference component detected by the phase detector 16, and Only the phase error that is corrected is corrected, and only the signal to be corrected is fed back in the loop of the second phase-locked loop, which will be described later.In other words, the audio carrier band pass filter 5, the phase detector 16, the local oscillator 17, and the mixer 18 The first phase-locked circuit (
After matching the phases of the two audio signals selected by the audio carrier band pass filters 14 and 15 through a loop of the PLL circuit, the audio carrier band pass filter 14, which further includes a first phase synchronization circuit, performs transmission conversion. A part of the output of the phase detector 16 is amplified through the amplifier 19 by the loop of the second phase-locked loop consisting of the transmission conversion local oscillator 11 and the power amplification section 12, and this component is sent to the phase shifter 6. In addition, phase modulation distortion at the output terminal 13, that is, AM-PM conversion occurring in the transmission conversion section 10 and the power amplification section 12, is automatically corrected. As explained above, in the first embodiment, the phase modulation distortion component is reduced by the feedback loop, so even if the AM-PM conversion characteristics change in the transmission converter 10, power amplifier 2, etc., it can be automatically followed. Therefore, there is an advantage that the correction characteristics of phase modulation distortion generated by AM-PM conversion do not change. FIG. 3 shows a second embodiment of the invention, and all symbols are the same as in FIG.

In the first embodiment, the phase shifter 6 is arranged in an intermediate frequency band (IF
In the second embodiment, the case where the phase shifter 6 is inserted at point P in FIG. 2 has been described. That is, the same effect can be obtained by inserting it at either point P or Q in FIG. 2 as long as it is in the correction loop. Therefore, as in the case of FIG. 3 which shows the case where the phase shifter 6 is inserted at the point P in FIG. 2, the case where the phase shifter 6 is inserted at the Q point in FIG. 2 is the same as in the first embodiment. effect is achieved.

The present invention is a feedback loop.

Since the phase modulation distortion due to AM-PM conversion is compensated for,
It has the advantage of being resistant to changes in operating conditions, and can be used in buzz beat compensators, intermodulation compensators, etc. in TV relay broadcasting equipment. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a system diagram of an AM-PM variable compensator of a conventional TV relay broadcasting device, FIG. 2 is a system diagram of the first embodiment of the present invention, and FIG. A system diagram of a second embodiment is shown.

1... Receiving antenna, 2... Input filter, 3... Receiving converter, 4... Local oscillator for receiving conversion, 5... Equalizer, 6... Phase shifter,
10...Transmission conversion unit, 11...Local oscillator for transmission conversion, 12...Power amplification unit 13
...Output terminal, 14, 15...Audio carrier band pass filter, 16...Phase detector, 17
・...−・Local oscillator, 18... Mixer, 19...
·amplifier.

Blind drawing Book 2 Disgusting figure 3

Claims (1)

[Claims] 1 In the phase modulation distortion correction method for TV relay broadcasting equipment,
a local oscillator that can externally control an error signal obtained by comparing the phases of a reference signal extracted by a filter from a circuit that generates nonlinear distortion and a signal obtained from a subsequent stage of the circuit using a phase detector; and feeds back to the local oscillator of the phase-locked circuit consisting of a mixer, a filter, and a phase detector so that the phases of the two signals become the same, and further outputs the output of the phase detector to eliminate the nonlinear distortion. A phase modulation distortion correction method characterized by controlling the phase by amplifying and feeding back to a phase shifter provided in the front stage of the generating circuit.