JP2623776B2 - Signal separation and demodulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] In the present invention, an image signal is subjected to pulse frequency modulation (hereinafter abbreviated as PFM modulation), and the signal is further subjected to pulse width modulation (hereinafter abbreviated as PWM modulation) with an audio signal or the like. The present invention relates to a multiplexed signal separation / demodulation method.

[Conventional technology]

Multiplexes image and audio signals (or data signals)
As a conventional technique for transmitting data using the M modulation method, there is known a technique in which a carrier frequency-modulated with an audio signal is frequency-division multiplexed (hereinafter abbreviated as FDM) outside the band of a baseband image signal. The separation and demodulation for this method is generally
It is known that a modulated signal is collectively demodulated into an FDM signal and then separated into a carrier frequency-modulated with a baseband image signal and an audio signal by a wave filter.

[Problems to be solved by the invention]

In the conventional multiplex modulation / demodulation method of the image signal and the audio signal described above, since the dynamic range of the PFM modulator is divided into the image signal and the audio signal, the respective modulation indices are lower than in the non-multiplexing case. / N decreases. Furthermore, since the image signal and the sound FM carrier signal are simultaneously PFM-modulated, if the nonlinearity and distortion characteristics of the PFM modulator are poor, the combined wave distortion interference or the sound FM carrier signal is phase-modulated by the image signal and the periodicity is reduced. There is a problem that noise, which is called buzz noise, increases.

In view of the above, the present invention has been made in order to solve such problems, and an object of the present invention is to modulate an image signal into a PFM, and further multiplex an audio signal or the like with the PFM modulation signal by PWM modulation. An object of the present invention is to provide a signal separation / demodulation circuit.

[Means for solving the problem]

The signal separation / demodulation circuit of the present invention employs the following means for separating / demodulating a multiplexed signal (abbreviated as PFM-PWM), which is obtained by performing PFM modulation on an image signal and then performing PWM modulation with an audio signal.

In other words, a PFM demodulation circuit consisting of a mono-multi circuit and a low-pass filter that keeps the pulse width constant for the input PFM-PWM modulation signal, a switch circuit that opens and closes the circuit only for a period proportional to the pulse width, and a triangular wave by the switch circuit A PWM demodulation circuit comprising a triangular wave generation circuit whose period of occurrence is controlled, a peak value envelope circuit for detecting the envelope of the peak value of the output of the triangular wave generation circuit, and a low-pass filter for removing high frequency components from the output of the envelope circuit. It consists of.

[Action]

Therefore, according to the present invention, it is possible to easily separate and demodulate a multiplex signal of a PFM-PWM modulation signal.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a signal separation / demodulation circuit according to the present invention. In the figure, a PFM-PWM signal input to a multiplexed signal input terminal 1 is branched into two, and on the side for demodulating this image signal, the pulse width is made constant by a mono-multi circuit 2 to remove a PWM modulation component, and the PFM-PWM signal is removed. Convert to a signal. After that, the signal is demodulated by a low-pass filter (LPF) 3 and image signal amplifier 4 which are general PFM demodulating means. On the other hand, on the side for demodulating the audio signal, the switch circuit 6 which performs the switching operation at the high level and the low level of the PFM-PWM signal controls on / off of the triangular wave generation circuit 7 to perform time-amplitude conversion. Then, after the peak value envelope circuit 8 takes the envelope of the peak value, it demodulates the signal through a low-pass filter (LPF) 9 and an audio signal amplifier 10. At this time, the output of the triangular wave generating circuit 7 has a constant inclination of the triangular waveform.

Next, the operation will be described. Here, it is assumed that the image signal is modulated at the pulse repetition frequency and the audio signal is modulated at the pulse width, and the PFM-PWM signal has a waveform as shown in FIG. 2 (a). When the PFM-PWM signal is input to the input terminal 1, the image signal of the PFM-PWM signal has the same pulse frequency as the PFM-PWM signal and the pulse width is made constant by the mono-multi circuit 2. That is, the signal is converted into a PFM signal by removing the PWM component, and the output has a waveform as shown in FIG. 2 (b). The output of the mono-multi circuit 2 is demodulated and amplified by the low-pass filter 3 and the amplifier 4, respectively, so that the demodulated output of the PFM signal as shown in FIG. It is taken out as a signal output.

On the other hand, when the PFM-PWM signal is input to the switch circuit 6, the switch circuit 6 performs a switching operation according to the high level and the low level of the PFM-PWM signal, and controls the triangular wave generation circuit 7. At this time, in the triangular wave generation circuit 7,
If the triangular waveform rises only during the high level period of the PFM-PWM signal, the output will have a waveform as shown in FIG. 2 (d). When this output is input to the peak value envelope circuit 8, the envelope circuit 8 takes the envelope of the peak value of the output of the triangular wave generation circuit 7, and the output has a waveform as shown in FIG. . Then, this output is demodulated and modulated by the low-pass filter 9 and the amplifier 10, respectively.
A demodulated output of the PWM signal as shown in FIG. 2 (f) is taken out as an audio signal output.

〔The invention's effect〕

As described above, according to the present invention, the image signal is provided with the pulse repetition frequency, and the audio signal is further provided with the pulse width change with respect to the pulse train.
A separation / demodulation circuit for a PFM-PWM modulation signal can be provided.
As a result, since each modulation index can be increased compared to the conventional multiplexing method, S / N can be improved, and coupled wave distortion and buzz noise caused by nonlinear distortion of the PFM modulator can be reduced. It has certain advantages.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing an example of waveforms of respective parts for explaining the operation of the above embodiment. 2. Mono-multi circuit, 3,9 Low-pass filter (LP
F) 4, image signal amplifier, 6 switch circuit, 7
…… Triangular wave generation circuit, 8 …… Peak value envelope circuit, 10 …… Audio signal amplifier.

Claims (1)

(57) [Claims] 1. A pulse frequency modulation-pulse width modulation (hereinafter referred to as PF)
For a signal, a PFM demodulation circuit consisting of a mono-multi circuit and a low-pass filter that keeps the pulse width constant, a switch circuit that opens and closes the circuit only for a period proportional to the pulse width, and a triangular wave formed by the switch circuit A triangular wave generating circuit whose generation period is controlled, a peak value envelope circuit for detecting an envelope of a peak value of an output of the triangular wave generating circuit, and a PWM demodulation circuit including a low-pass filter for removing high frequency components from the output of the envelope circuit. A signal separation / demodulation circuit characterized in that it is configured.