JPS63240195A - Transmitted multiplex signal regenerating device - Google Patents

Abstract

PURPOSE:To eliminate disturbance to TV broadcasting and to perform multiplex transmission and stable reception and regeneration by inverting and modulating a signal which is multiplexed with an orthogonal component at intervals of a horizontal scanning period. CONSTITUTION:A signal obtained by imposing residual side-band amplitude modulation on a carrier with a video signal and a signal obtained by imposing residual side-band amplitude modulation on a carrier in orthogonal phase with said carrier with another video signal is opposite-phase relation an intervals of the horizontal scanning period are multiplexed and received, and another modulated video signal is extracted by a BPF 12. A carrier regeneration block 13 which is formed of a carrier regenerating circuit 14 and a phase shifter 15 of pi/2 and supplied with said signal output a signal synchronized with the carrier to control a multiplex signal demodulating circuit 16 and a synchronous detecting circuit 17. Then the other video signal which is detected and demodulated and the video signal which is inverted by an inverting circuit 10 and demodulated are outputted through a switch 19 which is switched at intervals of the horizontal scanning period and a video signal processing circuit 21. This orthogonal modulation system reduces the disturbance to the TV broadcasting to receive and regenerate the multiplex video signal stably.

Description

[Detailed description of the invention] [Field of application in the skin industry] The present invention relates to a multiplex transmission system,
The present invention relates to a multiplex transmission signal reproducing device that receives a transmission signal in which other information is multiplexed on a 7 signal.

[Conventional technology]

Conventionally, a method for multiplexing other information in a television signal is described in Japanese Patent Laid-Open No. 49-84728, in which a carrier wave having an orthogonal phase relationship χ with a video carrier wave is modulated with other information and then modulated with the video signal. I was told that it is an orthogonal modulation method that combines it with a video carrier wave and transmits it.

In addition, as a method for reducing interference caused by multiplexed signals to current television receivers using this orthogonal modulation method, the Association has proposed applying the inverse characteristic of the Nyquist filter to the multiplexed signal on the transmitting side. IEICE technical research report published by IEICE Corporation, Vol. 8
6 No. 246, pages 65 to 72, November 1986
It is discussed in ``Transmission of high-definition images by orthogonal modulation of video carrier waves'', ``Communication method eS 86-82r'', published on May 27th.

[Problems that the invention aims to solve]

The above-mentioned conventional technology deals with interference caused by multiplexed signals when the detection method of current television receivers using orthogonal modulation method is envelope 4Ittli, or interference caused by low frequency components of multiplexed signals when using pseudo-synchronous detection of carrier wave reproduction difference. No consideration was given to interference to the color subcarriers of current television receivers, and there was a problem of interference with hue changes caused by multiplexed signals.

In addition, distribution B1. It didn't fade.

An object of the present invention is to provide a multiplex transmission method that is effective for stably receiving and reproducing multiplexed signals transmitted multiplexed to video carrier waves of current TV business broadcasting using an orthogonal modulation method that reduces interference with current TV business broadcasting. An object of the present invention is to provide a signal reproducing device.

[Means for solving the four points in between] The above purpose is to provide a receiver that demodulates the transmitted signal by modulating the orthogonal modulation of the video carrier wave using a multiplexed signal in reverse phase for each horizontal scanning period. Processing circuits such as inversion demodulation and comb filters? This can be achieved by providing

[Effect]

The processing circuit for each horizontal scanning period inverts and demodulates or inverts and adds the multiplexed signal transmitted multiplexed to orthogonal components.
It is possible to reduce interference from video signals transmitted through TVIL broadcasting.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a television receiver according to an embodiment of the present invention.

-1 is an antenna, 2 is a high frequency amplification circuit, 3 is a frequency conversion circuit, 4 is a reproduction IP filter for the receiver, 5 is an intermediate frequency amplification circuit, 6 is a video signal detection circuit, 7 is a video signal processing circuit, 8 is a A video signal output terminal, 9 an audio intermediate frequency amplification circuit, 10 an audio FMJflt wave circuit, 11 an audio signal output terminal, 12 a band pass filter, 13 a carrier wave regeneration block, 14 a carrier wave regeneration circuit, and 15 a transfer circuit. Aiki, 16
17 is a multiplexed signal demodulation circuit, 17 is a synchronous detection circuit, 18 is an inversion circuit, 19 is a switching circuit, 20 is a control circuit, 21 is another multiplexed video signal processing circuit, 22 is another multiplexed video signal This is the output terminal of

A television signal inputted from an antenna 1 is amplified by a high frequency amplifier circuit 2, frequency-converted to an intermediate frequency for demodulation by a frequency conversion circuit 5, and transmitted through a reproduction IF filter 4 for a receiver to an intermediate frequency amplifier circuit 5. Amplify with. Is the frequency conversion circuit 50 local oscillation frequency used for tuning? This is done by changing. The video signal band from the signal amplified by the intermediate frequency amplification circuit 5 is detected by a video signal detection circuit 6□, and the video signal is processed by the video signal detection circuit 7 to obtain a video signal at the video signal output terminal 8.

On the other hand, the audio signal band is amplified by the audio intermediate frequency amplification circuit 9, detected and demodulated by the audio FM detection circuit 10, and an audio signal is obtained at the audio signal output terminal 11.

The above is the same as a conventional television receiver.

In addition to the above, in order to reproduce another multiplexed video signal, the following operation is performed. A necessary band is selected from the output of the frequency conversion circuit 3 by a band pass filter 12, and a carrier wave regeneration block 13 composed of a carrier wave regeneration circuit 14 and a phase shifter 15 performs amplitude modulation using a signal synchronized with the regenerated carrier wave. Another video signal multiplexed and transmitted orthogonally to the component is detected and demodulated by the multiplex signal 41A circuit 16. The output video signal processing circuit 21 processes the signal and obtains it at the output terminal of another multiplexed video signal. In the multiplex signal demodulation circuit 16, the signal multiplexed and transmitted using the orthogonal components of the carrier wave is detected by the synchronous detection circuit 15, and the output signal and the signal inverted by the inversion circuit 18 are detected using the synchronous signal of the video signal processing circuit 7. Since the dflJ control circuit 20 and the switching circuit 19 switch each horizontal scanning period, the output of the multiplexed signal demodulation circuit 16 can demodulate the signal multiplexed into orthogonal components every horizontal scanning period. In addition, leakage from the video signal of the television broadcast, which appears in the output of the synchronous detection circuit 17 due to a phase error in the output signal of the carrier recovery block that synchronously detects the multiplexed signal, is also reversed every horizontal scanning period. Therefore, when another multiplexed video signal is displayed on the screen, the interference caused by leakage from the image signal is reversed every horizontal scanning period, making it more visible.

According to this embodiment, since the multiplexed signal demodulation circuit 16 inverts and outputs the signal after synchronous detection every horizontal scanning period, it is possible to demodulate a signal that is multiplexed and transmitted by inverting orthogonal components every horizontal scanning period. effective.

It also has the effect of reducing χ such as interference to the orthogonal component detection output of the video signal of the first video signal due to K such as ghosts.

An embodiment of the transmitter of the present invention that generates the signals transmitted in the above embodiments is shown in FIG. 51 is an input terminal for an audio signal, 32 is an F'M converter, a JI 4 unit, 63 is an audio signal carrier generator, 34 is an input terminal for a video signal, 35 is a video signal processing circuit, 36 is a video modulator, and 37 is a video signal. Signal carrier wave generator, 58 is an input terminal for another video signal to be multiplexed and transmitted, 59
is another video signal processing circuit, 40 is an inversion modulation Igli@,
41 is an inverting circuit; 42 is a switching circuit; 43 is a control circuit;
4 is a phase shifter, 45 is a modulator, 46 is an equalizer, 47 is an adder, 48 is a transmission V8B filter for residual sideband amplitude modulation, and 49 is an Ω calculator.

50 is an antenna.

The voice signal from the voice signal input terminal 31 is used as voice carrier tIJ1. from the voice signal carrier generator 53. F'M modulation 6
FM modulation is performed at 32. A video signal processing circuit 35 performs video signal processing for the video signal input to the video input 4 34 for television transmission, such as luminance signal processing and color difference signal processing of the 4 degree signal and the color difference signal.

Thereafter, the carrier wave from the interposed signal carrier wave generator 57 is modulated using the video modulator 36Y, and the transmission VSB filter 48 limits the band to the ten video broadcast band. Send.

The above nine points are the same as those of conventional terrestrial television broadcasting. The following is added in order to transmit another video signal to the above signals.

A video signal to be multiplexed is applied to the input terminal 38, and another video signal processing circuit 39 processes the video signal into a form that is easy to transmit, such as similar processing to the video signal processing circuit 66 described above. The inversion modulator 40 inverts and modulates the signal every horizontal scanning period. In the inversion modulator 40, the pressure control circuit 43 switches between the switching circuits 42 and 42 for each horizontal period.
The inversion circuit 41 switches another video signal between the inverted signal and the original signal every 1,000 periods, and the phase shifter 4 uses that signal.
A modulator 45 modulates the video 1M carrier wave whose phase has been shifted by 90 degrees through a modulator 45.

After that, the frequency characteristics of the output of the inverting modulator 40 are corrected by an equalizer 46 having characteristics inverse to those of the video reception IF' Nyquist filter, and the output is combined with a carrier wave modulated by the video signal by an mA unit 47 (7704). As a result, the video carrier wave is modulated in an orthogonal relationship with the video signal and another video signal. The equalizer 46 is used to ensure that the multiplexed signals have an orthogonal relationship when detecting the video of the Nyquist filter output of the television receiver. Since it is shown in "Transmission", it is omitted here. In addition, as another video signal to be multiplexed, regardless of whether it is related to the image being transmitted by television broadcasting, a still image or a television image that narrows the band by converting the time axis of a part of the screen. There are 74 possible types of signals.

According to the embodiment described above, another video signal that is multiplexed and transmitted in adjacent horizontal scanning periods is inverted and modulated. It has the effect of reducing interference from train signals. Note that a detailed explanation of the reason why interference can be reduced by inverting and modulating in adjacent horizontal scanning periods will be described later in FIGS. 5 and 6.

FIG. 5 shows the spectrum of the variable a4, and FIG. 4 shows a vector diagram of the modulation state of the video signal of the video carrier wave and the separate video signal.

In FIG. 3, 51 is the spectrum of the video signal after the V8B filter, 52 is the spectrum of the FM-modulated audio signal, and 55
shows the spectrum of another video signal. Here, the video signal spectrum 51 and the spectrum 52 of another video signal are shown divided into two stages in FIG.

The spectrum of another video signal to be multiplexed and transmitted is shown when the carrier wave is modulated in a band of 500 KHz. Note that the spectrum 52 of another video signal to be multiplexed and transmitted is shown as a spectrum with the characteristic sound of the equalizer 16 omitted.

In Figure 3, the spectrum below 75 MHz for the video carrier wave is attenuated by a VSB filter with vestigial sideband width modulation, 4.2 MHz.
For video signals up to 4.5 MHz, there is a spectrum in which the audio carrier wave is FM modulated near 4.5 MHz. Since both sidebands are transmitted for L75MHz on the video carrier wave, it can be considered as a general t4 (DAB).
If the imaging width of another video signal within 75 MHz is modulated in opposite phases every horizontal scanning period as A and -A, the carrier wave vector is cos (1) Ct±A sin when the video signal is 1. ω ct
(1) becomes. Here, ωC is the angular frequency of the carrier wave.

In addition, if the slope of the vSB filter is also taken into account, it will be 1 to 1.
25MH2 multiplex transmission is also possible.

In addition, we have noticed that orthogonal multiplexing interferes with the phase of video color subcarriers in current multiplex television broadcasting, which will be explained below. FIG. 5 shows a vector diagram χ of the color subcarrier on the video carrier. (-) indicates the case where there is no multiplexing on orthogonal components of the single-determined carrier wave, and (b) indicates the case where there is multiplexing on the orthogonal components. ω8 indicates the phase plane 6 k in the color subcarrier, ・st(′)s′
indicates that the phase of the color subcarrier due to adjacent horizontal scanning periods is shifted by π. ! -%-3 indicates the change process of the color subcarrier vector, and l-9 and l'~S'' indicate that the phase of the color subcarrier is shifted by π. Furthermore, A and -A are orthogonal components. This shows a case in which the signals are multiplexed to A and -A in adjacent horizontal scanning periods at a certain point.Due to the relationship between the frequency of the color subcarrier and the horizontal scanning frequency in current television broadcasting, the color subcarrier is transmitted in adjacent horizontal scanning periods. In the period le
me no O-,3 and j'lm-nl, ,l...
・The phase is shifted by π as shown by $1.

When multiplexing into orthogonal components is performed as shown in FIG. 5(b),
As shown in Fig. 4, when the video signal detection method is envelope compensation, the maximum amplitude of the color subcarrier is between S and 7 in the case of multiplexing A. appears and produces a ministerial phase difference φ with the maximum amplitude phase t in the case of drifting orthogonal components. The phase variation of the color subcarrier appears as a hue change on the reproduced video screen. This phase fluctuation occurs because when the video signal detection method is a synchronous detection method, only the component in the cosωct direction shown in the figure is detected, so even if there is multiplexing of A, the maximum amplitude phase of the color subcarrier is ! , and no phase fluctuation occurs.

In the case of a frozen wave, when orthogonal components are multiplexed into 7 and 1 (indicated by A and -A in Figure 5) according to the sign of the multiplexed signal, the phase direction (phase) of the maximum amplitude of the color subcarrier (lead and lag) are determined, and the amount of phase fluctuation is determined by the absolute values of A and -A.

The above explanation will be verified by calculation. Here, another video signal with a low frequency to be orthogonally multiplexed is: A Co5at, a video carrier wave to be multiplexed is a video signal with a low frequency of a television signal having cosωcty double sidebands gBcos bt
, the color subcarrier Y S cos st of the video signal, the output c (t) of the q calculator 170 is C (t) (1+
Bcos bt+8 cosst)cosωct+Ac
It is expressed as os at sinωCt (3). Here, at and bty are explained as -low frequency 5-number components in order to omit the complexity of calculation due to the level difference between the upper and lower sidebands due to the equalizer 16 and the Nyquist filter of the television receiver. . C(
S (t) by passing through Yf4B;y filter
The transmitted signal CT (t) excluding the component of cos (s - ωc)t, which is the lower sideband wave of + (Acos a t
-E-cos s t ) sinωct (4)
It is expressed as The Nyquist filter output CR(t) of the television receiver receiving this signal is at the video carrier frequency ω
It is converted to it.

+(Acos at-8cos s をdoor) cos (
ωit−θ) (5)

It is. From this CR(t), the envelope MA detection output 几o(t
x end+2BScosbt@cosst+2Scosst
-2AScos atesinst 10A”cos”
at) (7), and when the square root is approximately expanded, it becomes. Here, from o(t), s related to the color subcarrier
When the term t is extracted, the received color subcarrier T(,5(t
) is 2f';T"((1+Bcosbt+A" cos
"at) acos(s t+φ) (9) However.

The interference reduction described above is performed. Interference to existing television signal reception is reduced by utilizing the opposite polarity of the multi-I signal and the phase shift of the received interference and the reproduction method of visual or television signal perception. Figure 42 inverted material a4
When the phase of the multiplexed signal is changed to A and -AK in adjacent horizontal scanning periods by the circuit 40, as shown in FIG. 5(b), ω
, and ωS° are opposite directions, and the amount of phase fluctuation is the same. Therefore, the hue changes of the screen in adjacent horizontal scanning periods with the same signal are opposite, and the frequency characteristics of the color intuition of human vision (the eye In addition, in television receivers, a ``comb-shaped filter'' that correlates with the horizontal scanning period (so-called line correlation) is used to separate luminance signals from color signals. In such a receiver, the phase fluctuation of the color subcarrier can be canceled out using a circuit.
a) A configuration diagram of a comb filter for extracting a color signal for K general pleasure signal color signal separation, and (b) a waveform diagram for explaining the operation. 60 is an input terminal, 61 is a delay circuit, 6
2 is a subtracter 63 is an output terminal, and 64 to 67 are color subcarrier waveforms. 64 is when there is no multiplexing, 65 is on the right side of FIG. 51(b), 66 is on the left side of FIG. 5(b), 67 is 66
This is the inversion of The color subcarriers without multiplexing are shown in Figure 5 (
Corresponding to a), the time l is shown by the maximum width waveform 64.

When the multiplexed signal A is added here, the maximum amplitude appears between S and l, resulting in waveform 65. Further, in the next adjacent horizontal scanning period, the -A multiplexed signal is added, and the ωg'o color a carrier wave has a maximum loss phase between po and ', resulting in a waveform 66.

A waveform 65 and a waveform 66 delayed by one horizontal scanning period are applied to a subtracter 62 through a delay circuit 61 . The inversion of the waveform 66 is shown as a waveform 67, but subtracting the waveform 66 from the waveform 65 means adding the waveform 67 to the waveform 65, and further halving the amplitude results in the waveform 64. This waveform 64 is obtained from the output terminal 63. It is shown that the color subcarrier obtained by this comb filter does not undergo a phase change IIh even if the video signal detection method is envelope detection and multiplexed signals are added.

As described above, since multiplexing is performed in reverse phase for each horizontal scanning period, there is an effect that interference with the hue of existing television receivers can be reduced.

Another embodiment of the invention is shown in FIG. 71 is a phase shifter, 7
2 is a synchronous detection circuit, and the same reference numerals as in FIG. 1 indicate the same functions. The difference from FIG. 1 is that a phase shifter 71 for obtaining a recovered carrier wave with a different π phase shift from the phase shifter 15 is provided in the carrier recovery block 13, and a synchronous detection circuit 72 is provided in the multiplex signal demodulation circuit 16. , a signal multiplexed with orthogonal components of the carrier wave is obtained as a signal synchronously detected in two phases of normal rotation and inversion, and is output from the synchronous detection circuit 15 and synchronous detection circuit 72, and is transmitted by the control circuit 20 in each horizontal scanning period. This is the point at which the switching circuit 19 is switched.

According to this embodiment, multiplexed signals can be demodulated in the same way as in FIG. 1, and in addition to the effect of reducing interference from television video signals, the horizontal This also has the effect of reducing even a slight time difference between the output signals of the multiplexed signal 41 modulation circuit 16 for each period.

Still another embodiment of the invention is shown in FIG. Components with the same symbols as in FIG. 1 or FIG. 7 indicate the same functions. The difference from FIG. 1 or FIG. 7 is that the carrier recovery block 15
The outputs of the phase shifter 15 and phase shifter 71 are applied to the synchronous detection circuit 17 via the switching circuit 19 in the multiplex signal demodulation circuit 16. The switching circuit 19 is controlled by the control circuit 20 for each horizontal scanning period to switch the two-phase carrier wave of normal rotation and inversion of the orthogonal component of the carrier wave and apply it to the synchronous detection circuit 17. 16
It is possible to demodulate a signal that is multiplexed and inverted into orthogonal components during the horizontal scanning period on the output of the horizontal scanning period.

According to this embodiment, multiplexed signals can be demodulated in the same way as in FIG. The output of the signal demodulation circuit 16 is affected by fluctuations in each horizontal set period due to the DC voltage difference or gain difference between the two synchronous detection circuits or the DC voltage difference or gain difference between the synchronous detection circuit and the inverting circuit, or glitches due to switching of the switching circuit. It also has the effect of eliminating.

Still another embodiment of the present invention is shown in FIG. 1st
Items with the same symbols as in the figure indicate the same functions.

The difference from FIG. 1 is that a signal from another multiplexed video signal processing circuit 21 is used instead of the video signal processing circuit 7 for switching control of the control circuit 20 for each horizontal scanning period.

According to this embodiment, in addition to the effects shown in FIG. 1, since the multiplexed signals from another video signal processing circuit are input, the multiplexed signals include switching control signals, etc. Multiplex transmission also has the effect of making it possible to perform even more complex or accurate switching control.

Although FIG. 9 is a modification of FIG. 1, the same effect can be obtained in FIG. 7 or 8 by replacing the control circuit 200 Å with the video signal processing circuit 21. Furthermore, it is also possible to use both the video signal processing circuit 7 and the video signal processing circuit 21 as inputs.

As described above, although the control circuit 20 in FIG. 1, FIG. 7, FIG. 8, or FIG. 9 is switched every horizontal scanning period, the control timing is determined using a vertical synchronizing signal in addition to the horizontal synchronizing signal. There is no need to mention that it is good.

Another embodiment of the invention is shown in FIG. 1 is a multiple signal demodulation circuit, 102 is a delay circuit, and 103 is a subtracter, and the same symbols as in FIG. 1 indicate the same functions. The difference from FIG. 1 is that when performing A after detection in the multiplex signal demodulation circuit 16 using the carrier wave regenerated by the carrier wave recovery block 13, the output signal detected by the synchronous detection circuit 17 and the delay circuit 102 are transmitted for one horizontal scanning period. The purpose is to subtract the delayed signal and the subtracter 103.

This subtraction reduces interference from the video signal of the television broadcast. The process will be explained below. If you send another multiplexed video signal at a certain timing in a horizontal scanning period at a level of Even at the same timing as described above in the horizontal scanning period, another video signal is at the level of X, but since the modulation is inverted at this time, it is sent at the level of X. The delay device 44 and subtracter 45 of the receiver calculate the X value received one horizontal scanning period ago.
Since X received in the next horizontal scanning period is subtracted at the same timing, it becomes X - (X) - 2X (11), and a signal twice as large is obtained. If G interference is received from the video signal of television broadcasting during this transmission, since the video signal generally has a lot of correlation like the horizontal scanning period,
It will be interfered with by G both at the timing of and at the timing of X. The subtracter 58 yields (X+G)-(X+G)-2X (12), and the interference from the video is canceled out. However, if there is little correlation between horizontal scanning periods on the screen of the video signal, the cancellation effect will be small.

According to the embodiment described above, it is possible to reduce interference from television video signals such as ghosts.

〔Effect of the invention〕

According to the present invention, it is possible to perform inversion demodulation or inversion addition demodulation of a signal multiplexed into orthogonal components for each horizontal scanning period, so that the signal t which is inverted modulated and multiplexed for each horizontal scanning period
``4Iv4'', and it also has the effect of reducing interference from the video signal of the television signal leaked to the orthogonal component due to ghosts and the like.

[Brief explanation of drawings]

FIG. 1 is a television receiver according to an embodiment of the present invention. FIG. 3 is a spectrum diagram for explaining the present invention. FIG. 4 is a vector diagram for explaining the present invention. FIG. 5 is a diagram for explaining the present invention. A vector diagram of color subcarriers for explanation of 12...Band pass filter, 15...Carrier recovery block, 14...Carrier recovery circuit, 15.71...
Phase shifter, 16.101...Multiple signal demodulation circuit, 17.
72... Synchronous detection circuit, 18... Inversion circuit, 19.
...Switching circuit, 20--Control circuit, 21--Another multiplexed video signal processing circuit, 40--Inversion modulation circuit, 46--Equalizer, 47--Adder. f'-

Claims (1)

[Claims] 1. A device for receiving and reproducing a signal transmitted by modulating the amplitude of a residual sideband of a carrier wave with a video signal, wherein the residual sideband amplitude modulates a carrier wave with a video signal, and receives and reproduces the transmitted signal, wherein the residual sideband amplitude modulates a carrier wave with a video signal, and receives and reproduces the transmitted signal, wherein the residual sideband amplitude modulates a carrier wave with a video signal, A carrier wave that receives as input a multiplexed transmission signal that is modulated with a multiplexed signal other than a video signal transmitted by sideband amplitude modulation and is transmitted after being combined with the residual sideband amplitude modulated wave, and reproduces a carrier wave from the multiplexed transmission signal. A regeneration circuit and a multiplex signal demodulation circuit that receives the multiplexed transmission signal as input and demodulates and outputs the multiplexed signal that is modulated in an opposite phase relationship every certain period of time using the output of the carrier regeneration circuit. Multiplex transmission signal reproducing device. 2. The apparatus according to claim 1, wherein the multiplex signal demodulation circuit receives the multiplex transmission signal as an input and reproduces a carrier wave that is orthogonal to the carrier wave that is the output of the carrier wave regeneration circuit and is modulated by the video signal. A synchronous detection circuit that performs synchronous detection using a carrier wave, an inverting amplifier circuit that receives the output of the synchronous detection circuit as an input and obtains an inverted output, and an output that receives the output of the synchronous detection circuit and the output of the inverting amplifier circuit as inputs. A multiplex transmission signal reproducing device comprising: a switching circuit that switches to an output; and a control circuit that switches the switching circuit for each synchronization signal of the video signal. 3. The apparatus according to claim 1, wherein the multiplex signal demodulation circuit is configured to receive the multiplex transmission signal and have a quadrature phase with the carrier wave modulated by the video signal which is the output of the carrier wave regeneration circuit. a first synchronous detection circuit that performs synchronous detection using one regenerated carrier wave, and a second synchronous detection circuit that performs synchronous detection using a second regenerated carrier wave that is in opposite phase to the first regenerated carrier wave and has a quadrature phase with the carrier wave modulated by the video signal. a switching circuit that takes the first synchronous detection circuit and the second synchronous detection circuit as inputs and selectively switches them to output; A multiplex transmission signal reproducing device comprising a switching control circuit. 4. The apparatus according to claim 1, in which the multiplexed signal demodulation circuit is connected to a first regenerated carrier wave which is an output of the carrier wave regeneration circuit and has a quadrature phase with a carrier wave modulated with the video signal; a switching circuit that receives as input a second reproduced carrier wave which is opposite in phase to the first reproduced carrier wave and has a phase orthogonal to the carrier wave modulated by the video signal and selectively switches to the output; A multiplex transmission signal reproducing device comprising: a synchronous detection circuit that synchronously detects multiplex transmission signals; and a control circuit that switches the switching circuit for each synchronization signal of the video signal. 5. In the apparatus according to claim 1, the multiplexed signal demodulation circuit receives the multiplexed signal as an input, and generates a reproduced carrier wave which is the output of the carrier wave regeneration circuit and has a phase orthogonal to the carrier wave modulated by the video signal. 1. A multiplex transmission signal reproducing device comprising: a synchronous detection circuit that performs synchronous detection; and a comb filter that selectively passes the output of the synchronous detection circuit. 6. The apparatus according to claim 5, wherein a delay circuit causes the comb filter to delay the output signal of the synchronous detection circuit by a time corresponding to the fixed period, and the output signal of the delay circuit and the A multiplex transmission signal reproducing device comprising: a calculation circuit that calculates a signal output from a synchronous detection circuit.