JPH07105774B2 - Transmission signal reproduction device - Google Patents

Description

The present invention relates to a multiplex transmission system, and more particularly to a PC for video signals.
The present invention relates to a reproducing device that receives a signal of a transmission method effective for multiplexing and transmitting an M audio signal.

[Prior Art] For the method of multiplexing digitally encoded PCM audio signals and video signals, see "Satellite Broadcasting", Part 1 of the Satellite Broadcasting Receiving Technology Study Group Report, published by the Institute of Radio Technology, June 1983. Although it is reported in "Receiver" etc., the current terrestrial television broadcasting band is not satisfied because the PCM audio signal is multiplexed with the current NTSC video signal using the 5.7272 MHz subcarrier. It is difficult to use for John broadcasting.

On the other hand, the possibility of multiplex transmission to the current terrestrial television broadcasting is discussed from page 205 of the Broadcasting Techniques 2 “Broadcasting Method” edited by the Japan Broadcasting Corporation in January 1983.
Although it is described on page 08, there is no description about a system capable of securing a transmission capacity of about 1 Mbit / sec for transmitting two channels of high quality voice.

[Problems to be solved by the invention]

The above-mentioned conventional technology is of high quality for current terrestrial television broadcasting.
There was no method for multiplex transmission of PCM audio signals.

It is an object of the present invention to provide a reproducing device for stably receiving and reproducing those signals when other signals are multiplexed and transmitted on the amplitude-modulated signal, and particularly high quality is applied to current terrestrial television broadcasting. Another object of the present invention is to provide a transmission signal reproducing apparatus which is effective in stably receiving and reproducing a signal of a transmission system in which multiplex signals such as digitally encoded PCM audio signals are multiplexed and transmitted.

[Means for solving problems]

The above-mentioned purpose is that, in the current terrestrial television broadcasting, the video signal carrier wave is amplitude-modulated by the video signal and is transmitted by the vestigial sideband. In a receiver that receives and reproduces a signal that has been quadrature-carrier-suppressed and amplitude-modulated by a PCM audio signal and is multiplexed and transmitted, set the demodulation intermediate frequency of the PCM audio signal that is multiplexed and transmitted to be lower than the intermediate frequency for video signal demodulation. This will be achieved.

[Action]

By setting the demodulation intermediate frequency of the multiplex-transmitted PCM audio signal to a low frequency, synchronization due to the internal delay time of the synchronous detection means for demodulating the PCM audio signal, the delay time between input signal paths, and their fluctuations Since the phase error of the detection can be reduced, the signal can be demodulated stably.

〔Example〕

FIG. 1 shows an example of a receiver in the case where a digitally encoded PCM audio signal is multiplexed and transmitted to a current terrestrial transmission television as one embodiment of the present invention.

1 is an antenna, 2 is a high frequency amplification circuit, 3 is a first frequency conversion circuit, 4 is an intermediate frequency amplification circuit, 5 is a video signal detection circuit, 6 is a video signal amplification circuit, 7 is a color difference signal demodulation circuit, 8
Is a primary color signal demodulation circuit, 9 is a cathode ray tube, 10 is an audio intermediate frequency amplification circuit, 11 is an audio FM detection circuit, 12 is an audio signal output terminal, 13 is a first band pass filter, 14 is a second frequency conversion circuit, 15 is a second band-pass filter, 16 is a synchronous detection circuit, 17 is a carrier recovery circuit, 18 is a code identification circuit, 19 is a clock recovery circuit, 20 is a digital signal processing circuit, 21 is a digital-analog conversion circuit (hereinafter DAC 22) is an output terminal for the multiplex-transmitted PCM audio signal.

The television signal input from the antenna 1 is amplified by the high frequency amplifier circuit 2, frequency-converted to the intermediate frequency for demodulation by the frequency conversion circuit 3, and amplified by the intermediate frequency amplifier circuit 4. The tuning is performed by changing the local oscillation frequency of the frequency conversion circuit 3. The video signal band is detected by the video signal detection circuit 5 from the signal amplified by the intermediate frequency amplification circuit 4,
From the luminance signal output from the video signal amplifier circuit 6 and the color difference signal output from the color difference signal demodulation circuit 7, R, G,
Obtain the three primary colors of B and project them on the cathode ray tube 9.

On the other hand, regarding the audio signal band, the audio intermediate frequency amplifier circuit
The signal is amplified at 10 and detected and demodulated by the audio FM detection circuit 11 to obtain an audio signal at the audio signal output terminal 12. The above is the same as that of the conventional television receiver.

In addition to the above, in order to demodulate the digitally encoded PCM voice signal, the output of the first frequency conversion circuit 3 is passed through the first bandpass filter 13 and then further output by the second frequency conversion circuit 14. The frequency is converted into an intermediate frequency of a low frequency and the second band pass filter 15 is passed. PC multiplexed by the first and second bandpass filters 13 and 15
The M audio signal band is selected and amplified, and the synchronous detection circuit 16 uses the carrier orthogonal to the video signal carrier reproduced by the carrier reproduction circuit 17 to detect and demodulate the multiplexed signal multiplexed and transmitted on the orthogonal carrier. The signal obtained as a result is converted into a digital code by the code identifying circuit 18 at the point where the error rate is small, and the error occurred during transmission is detected and corrected by the digital signal processing circuit 20 using the error detection and correction code. The clock recovery circuit 19 is a circuit that extracts the transmission clock from the signal output from the synchronous detection circuit 16, and has a small error rate in the signal output from the synchronous detection circuit 16 (so-called maximum opening of the eye pattern).
It is necessary to convert to digital code. The digital code after the error detection and correction is converted into an analog signal by the DAC 21 to be converted back into a voice signal, which is obtained at the output terminal 22 of the multiplex-transmitted PCM voice signal.

According to the present embodiment, the video signal is demodulated at the intermediate frequency of the output of the first frequency conversion circuit 3 (58.75 MHz is commonly used in Japanese terrestrial broadcasting television).
Since the audio signal PCM transmitted at the intermediate frequency of the output of the second frequency conversion circuit 14 having a lower frequency (for example, about 5 MHz) is demodulated, the carrier wave reproduced by the carrier wave reproduction circuit 17 used in the synchronous detection circuit 16 is reproduced. The phase error due to the circuit delay time is reduced by lowering the frequency, and there is an effect that it is possible to demodulate stably multiplexed PCM audio signals.

FIG. 2 shows an embodiment of a transmitter that generates the signal transmitted in the above embodiment. 23 is an audio signal input terminal, 24 is an FM modulator, 25 is an audio signal carrier generator, 26 is a video signal input terminal, 27 is a matrix circuit, 28 is a luminance signal processing circuit, 29
Is a color difference signal processing circuit, 30 is an adding circuit, 31 is a video modulator,
32 is a video signal carrier generator, 33 is an input terminal for an audio signal multiplexed and transmitted as a PCM audio signal, 34 is an analog / digital converter (hereinafter abbreviated as ADC), 35 is a digital signal processing circuit, and 36 is a low-pass filter. Filter, 37 is 90 degree phase shifter, 38
Is a modulator for PCM audio signals, 39 is an adder, 40 is a VSB filter for vestigial sideband amplitude modulation, 41 is an adder, and 42 is an antenna.

The audio signal carrier from the audio signal carrier wave generator 25 is FM-modulated in the FM modulator 24 by the audio signal from the audio signal input terminal 23. The RGB three primary color signals input to the video signal input terminal 26 are divided into a luminance signal and a color difference signal by a matrix 27, processed by a luminance signal processing circuit 28 and a color difference signal processing circuit 29, respectively, and then added by an adder 30. The audio signal which is the signal after addition is modulated from the video signal carrier from the video signal carrier generator 32 by using the video modulator 31 and band-limited to the television broadcast band by the VSB filter 40 and FM-modulated by the adder 41. It is additively combined with the carrier wave and transmitted from the antenna 42.

The above is the same as the conventional terrestrial television broadcasting. The following is added to multiplex transmission of high quality PCM audio signals to the above signals.

Input terminal 3 for audio signals multiplexed and transmitted as PCM audio signals
In addition to 3, the voice signal is converted into a digital code by ADC34,
The digital signal processing circuit 35 adds a code for detecting and correcting an error that occurs during transmission, and performs interleaving processing, etc., and unnecessary high frequency components are passed through the low pass filter 36 suitable for the transmission rate of the digital code. To delete.
With this digital coded PCM audio signal, a 90 ° phase shifter 37 is used to modulate a 90 ° phase-shifted video signal carrier with a PCM audio signal modulator 38 and an adder 39 to modulate the video signal. The added video signal carrier is added. As a result, the video signal carrier is modulated in a quadrature relationship with the video signal and the PCM audio signal.

The modulated spectrum is shown in FIGS. 3 and 4, and a vector diagram of the modulation state of the video signal of the video signal carrier and the PCM audio signal is shown in FIG. 43 of FIG. 3 is a spectrum of the modulated video signal after the VSB filter, 44 is a spectrum of the FM-modulated audio signal, and PC of 45 is modulated in FIG.
M shows the spectrum of the audio signal. Here, the spectrum of the PCM audio signal is the roll-off rate at a transmission rate of 1 Mbit / sec.
The spectrum when a quadrature carrier is modulated with a signal of 0.5 is shown.

In Fig. 3, vestigial sideband amplitude modulation is applied to the spectrum below -0.75MHz with respect to the video signal carrier.
Attenuated by VSB filter. Up to 4.2MHz, there is a spectrum where the audio signal carrier is FM modulated near the video signal 4.5MHz. Since both sidebands are transmitted at ± 0.75 MHz with respect to the video signal carrier, it can be considered as general amplitude modulation (DSB). It is ± 0.75 as shown in Fig. 4 orthogonal to the video signal carrier that has both sidebands.
When signals within MHz are made to correspond to digital codes 1 and 0 and carrier suppression amplitude modulation is performed with amplitudes A and −A, the vector of the video signal carrier is cosωct ± A sinωct (1) when the video signal is 1. Become. Where ωc is the angular frequency of the carrier. (1)
When you expand the expression Is.

Consider the interference from the PCM audio signal to the received video signal. In the case where the video signal detection circuit synchronously detects cosωct, regardless of the value of A, only the coefficient of cosωct (that is, only the video signal) is reproduced and no interference occurs. In the case where the video signal detection circuit performs envelope detection, lowering the value of A from 1 can reduce interference. For example, if A is 0.1, Therefore, a signal of 0.005 (about -40dB) is affected compared to 1, but I think that there is no practical problem if the SN ratio of the video signal is 40dB or more. Furthermore, if A is lowered below 0.1, the influence on the video signal is further reduced.

On the other hand, the interference of the PCM audio signal from the video signal to the detection circuit is caused by the synchronous detection circuit 16 synchronously detecting only the signal multiplexed and transmitted by the orthogonal carrier orthogonal to the video signal carrier as shown in FIG. Can be eliminated. Considering the signal level-to-noise ratio (hereinafter referred to as the SN ratio), assuming that the SN ratio of the video signal is 40 dB, the bandwidth is about 4 times that of the transmission bandwidth of 1 MHz of the PCM audio signal. The SN ratio of the PCM audio signal is 46 dB, but the modulation level A of the PCM audio signal is
If it is 0.1, the SN ratio will be about 26 dB.

On the other hand, considering the relationship between the SN ratio of a digital signal and the bit error rate as a general binary signal, the SN ratio is 17.4 dB and the bit error rate is 1 × 10 ⁻⁴ . The SN ratio of the video signal is
In the case of 40 dB, the SN ratio of the PCM audio signal is 26 dB, which is a practically sufficient value for digital signal transmission.

Another embodiment of the present invention is shown in FIG. The received signal is the same as in the case of FIG. 1, and the same reference numerals as those in FIG. 1 indicate the same functions. 14 is a second frequency conversion circuit, 46 is a mixing circuit,
47 is a voltage controlled local oscillator, 49 is a reference signal generator, 50
Is a low pass filter, the second frequency conversion circuit 14 of FIG.
Is composed of a mixing circuit 46 and a voltage controlled local oscillator 47.

The difference from FIG. 1 is that in FIG. 1, the orthogonal carrier orthogonal to the video signal carrier reproduced by the carrier reproducing circuit 17 is reproduced and multiplexed by the synchronous detection circuit 16 to the orthogonal carrier orthogonal to the video signal carrier. Compared to the detection of PCM audio signals, in Fig. 6, the phase relationship between the video signal carrier and the quadrature carrier is almost quadrature, and the fact that the DC component of the modulation by the PCM audio signal is small is used. , Reference signal generator
The phase difference between 49 and the intermediate frequency signal including the carrier wave is detected by the synchronous detection circuit 16 and the low-pass filter 50, and is fed back to the voltage controlled local oscillator 47 to generate the intermediate frequency image signal carrier wave and the reference signal. The output of the synchronous detection circuit 16 is used as a detection output by synchronizing the output of the detector with the quadrature relationship at the same frequency.

According to the present embodiment, the demodulation frequency drift due to the frequency drift of the first frequency conversion circuit 3 and the like is small because it is the negative feedback loop in which the intermediate frequency for demodulation matches the frequency of the reference frequency 49. There is an effect that demodulation can be performed more stably than the embodiment shown in FIG.

FIG. 7 shows still another embodiment of the present invention. Reference numeral 56 is a phase shifter, 57 is a third band-pass filter, and 58 is a PLL circuit. The same reference numerals as in FIG. A video signal carrier is extracted from the output of the second frequency conversion circuit 14 using the third band pass filter 57, and a carrier signal for reproduction synchronized with the video signal carrier is obtained by the PLL circuit 58 to obtain a phase shifter.
It is sent to the synchronous detection circuit 16 using 56. Others are the same as those in FIG. 1, but according to the present embodiment, the third band pass filter is used.
Since it is used only to reproduce the carrier signal for reproduction synchronized with the video signal carrier by using the 57 and the PLL circuit 58, it is possible to design with less influence on other signals, so that it is possible to demodulate the signal more stably. is there.

FIG. 8 shows another embodiment of the present invention. Reference numeral 60 is a phase shifter, 61 is a reference signal generator, 62 is a synchronous detector, and 63 is a low-pass filter. The same reference numerals as in FIGS. 1, 6 and 7 indicate the same functions. A video signal carrier is extracted from the output of the second frequency conversion circuit 14 using a third band pass filter 57, and the phase difference between the video signal carrier and the output of the reference signal generator 61 is detected by the synchronous detection circuit 62 and the low Detected by the band pass filter 63, fed back to the voltage-controlled local oscillator 47, the video signal carrier frequency of the output of the second frequency conversion conversion circuit 14 and the frequency of the reference signal generator 61 are matched, and the phase is shifted. The device 60 absorbs a delay time difference between the second band-pass filter 15 and the third band-pass filter 57 and sends it to the synchronous detection circuit 16 as a carrier signal for synchronous detection.

According to the present embodiment, the feedback loop formed by the third bandpass filter 57 synchronous detection circuit 62 or the like is used only for obtaining the carrier signal for synchronous detection that matches the video signal carrier, and therefore has less influence on other signals. Since it can be designed, there is an effect that the signal can be demodulated more stably.

〔The invention's effect〕

According to the present invention, a quadrature carrier having a phase of approximately 90 degrees is modulated with a PCM audio signal to a video signal carrier that is amplitude-modulated with a video signal, and an intermediate frequency for receiving and reproducing a signal that is multiplexed and transmitted is changed to a video signal. Since it can be set to a frequency lower than the intermediate frequency for demodulation, the synchronous detection phase error due to the internal delay time of the synchronous detection means for demodulating the PCM audio signal, the delay time between the input signal paths and their fluctuation can be reduced,
It has the effect of stable demodulation.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of an embodiment of a transmitting side for carrying out the present invention, FIG. 3 is a spectrum diagram for explaining the present invention, and FIG. FIG. 5 is a spectrum diagram for explaining the present invention, FIG. 5 is a vector diagram for explaining the present invention, FIG. 6 is a configuration diagram of another embodiment of the present invention, and FIG. 7 is still another embodiment of the present invention. FIG. 8 is a block diagram of an example, and FIG. 8 is a block diagram of another example of the present invention. 13,15,57 …… Bandpass filter, 16,62 …… Synchronous detection circuit, 17 …… Carrier recovery circuit, 18 …… Code identification circuit, 19 …… Clock recovery circuit, 20 …… Digital signal processing circuit, 21 ...... DAC, 46 …… Mixed circuit, 47 …… Local oscillator, 49,61 …… Reference signal generator, 50 …… Low pass filter, 56,60 …… Phase shifter.

Claims (5)

[Claims] 1. A basic signal band in which a video carrier is amplitude-modulated by a vestigial sideband with a video signal, and a quadrature carrier whose phase is different from the video carrier by about 90 degrees has a double sideband in the vestigial sideband. A multiplexed television modulated by a digitally coded signal so that the video carrier modulated by the vestigial sideband amplitude modulation and the orthogonal carrier modulated by the digitally coded signal are transmitted. A transmission signal reproducing device for receiving a digital signal and reproducing a digitally encoded signal, the receiving frequency converting means for receiving the multiplexed television signal and converting it to a first intermediate frequency for demodulation, A video signal demodulating means for demodulating a video signal from the output signal of the receiving frequency converting means; and a signal modulated and transmitted to the orthogonal carrier wave of the output signal of the receiving frequency converting means. First bandpass filter means for passing a band in which the present signal band exists; intermediate frequency conversion means for converting an output signal of the first bandpass filter means into a second intermediate frequency for demodulation; Carrier reproduction means for reproducing a carrier wave for quadrature detection for detecting a signal modulated and transmitted to the orthogonal carrier wave from an output signal of the frequency conversion means, and an output signal of the intermediate frequency conversion means for outputting the carrier wave reproduction means. And a synchronous detection means for demodulating a signal that is transmitted after being synchronously detected with a signal and modulated into the orthogonal carrier wave. 2. The transmission signal reproducing apparatus according to claim 1, wherein the audio signal is a digitally encoded audio signal as the digitally encoded signal. 3. A video signal is vestigial sideband amplitude modulated with a video signal, and a quadrature carrier whose phase is substantially 90 degrees different from the video carrier has a basic signal band within a band having double sidebands within the vestigial sideband. A multiplexed television modulated by a digitally coded signal so that the video carrier modulated by the vestigial sideband amplitude modulation and the orthogonal carrier modulated by the digitally coded signal are transmitted. A transmission signal reproducing device for receiving a digital signal and reproducing a digitally encoded signal, the receiving frequency converting means for receiving the multiplexed television signal and converting it to a first intermediate frequency for demodulation, Video signal demodulating means for demodulating a video signal from the output signal of the receiving frequency converting means, and a first band-pass filter for passing the signal band of the output signal of the receiving frequency converting means. A stage, an intermediate frequency conversion unit for converting the output signal of the first band-pass filter unit into a second intermediate frequency for demodulation, a signal band of the output signal of the intermediate frequency conversion unit, and the first band Second band pass filter means for passing a band in which the basic signal band of the signal modulated and transmitted to the orthogonal carrier wave by the combination with the band pass filter means of: and an output of the second band pass filter means Carrier recovery means for reproducing a carrier for quadrature detection for detecting a signal modulated and transmitted to the quadrature carrier, and an output signal of the second band pass filter means by an output signal of the carrier recovery means. And a synchronous detection means for synchronously detecting and demodulating a signal which is modulated by the orthogonal carrier wave and transmitted. 4. The intermediate frequency conversion means according to claim 3, wherein the intermediate frequency conversion means is constituted by a mixing means for frequency-converting by multiplying the voltage-controlled oscillation means and the voltage-controlled oscillation means, and the carrier recovery means is used as a reference signal. The voltage control oscillation means is constituted by an oscillating means, and a low-frequency signal having a phase difference between the output signal of the second band pass filter means detected by the synchronous detection means and the reference signal oscillating means is passed to the voltage control oscillating means. A transmission signal reproducing device, characterized in that low-pass filter means is provided. 5. A transmission signal reproducing apparatus according to claim 3, wherein the audio signal is a digitally encoded audio signal as the digitally encoded signal.