JPS6136428B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting luminance signals, chromaticity signals, and audio signals in a color television receiver, and in particular to a method for detecting a chromaticity signal of high quality without cross-color interference. This is what I did.

FIG. 1 shows a conventional normal detection method, in which a received signal from an antenna 11 is supplied to a tuner 12 to obtain a video intermediate frequency signal, which is extracted through a video intermediate frequency amplifier 13, and the video intermediate frequency signal is output to one side. The first envelope detector 15 detects the luminance signal and the chromaticity signal, and the video intermediate frequency signal is supplied to the second envelope detector 15 through the audio trap circuit 14. Detector 16
The second detector 16 detects the audio intermediate frequency signal.

However, this method requires a high-level video intermediate frequency signal, and has the drawbacks of orthogonal distortion and cross-color interference, which are decreasing as circuits are increasingly integrated into ICs.

There is also a method that performs envelope detection of the luminance signal and chromaticity signal separately. In FIG. 2, the received signal of the antenna 21 is supplied to the tuner 22 to obtain a video intermediate frequency signal, which is extracted through the video intermediate frequency amplifier 23, and the video intermediate frequency signal is then transmitted through the audio trap circuit 24 to the video intermediate frequency signal. In this case, the audio trap circuit 24 is configured such that the audio carrier intermediate frequency is attenuated very greatly so that the color subcarrier intermediate frequency is also sufficiently attenuated. The first detector 25 detects the luminance signal, and the video intermediate frequency signal is supplied to the second envelope detector 26, which detects the chromaticity signal and the audio intermediate frequency signal. is detected.

However, although this method also eliminates the interference of the audio signal with respect to the luminance signal, it has the disadvantage that cross-color interference occurs, similar to the method shown in FIG.

On the other hand, there is a method in which luminance signals, chromaticity signals, and audio signals are detected by synchronous detection. Third
The figure shows a general system in which a received signal from an antenna 31 is supplied to a tuner 32 to obtain a video intermediate frequency signal, which is supplied to a synchronous detector 34 through a video intermediate frequency amplifier 33, and this synchronous detector At 34, synchronous detection is performed using a reference carrier having the same frequency and phase as the video intermediate carrier to detect a luminance signal, a chromaticity signal, and an audio intermediate frequency signal, and the audio intermediate frequency signal is extracted through an audio intermediate frequency amplifier 35. .

However, in this method, the synchronous detector 34
For this reason, for example, the second harmonic of the luminance signal component, which is 460 kHz apart from the video carrier intermediate frequency, and the beat of the audio intermediate carrier wave are mixed into the chromaticity signal. cross-color interference due to the low-frequency components of the video carrier, and
There is a drawback that the second harmonic of the luminance signal component, which is 2.25MHz apart, mixes into the audio signal and generates a buzz. In systems in which a carrier wave is formed, this becomes noticeable due to the poor purity of the reference carrier wave, and in some cases, cross-color interference and buzz may be greater than in envelope detection systems.

There is also a method of separately synchronously detecting the video signal and the audio signal. FIG. 4 shows that the reception signal of the antenna 41 is supplied to the tuner 42 to obtain a video intermediate frequency signal, which is taken out through the preamplifier 43, and the video intermediate frequency signal is transmitted to the first
is fed to a first synchronous detector 45 through a video intermediate frequency concentration filter 44, in which case the filter 44 traps the audio carrier intermediate frequency f _s as shown by curve 1 in the figure, and also traps the color subcarrier intermediate frequency f _c The first synchronous detector 45 performs synchronous detection with a reference carrier wave having the same frequency and phase as the video intermediate carrier wave, and the first synchronous detector 45 detects the luminance signal and the image intermediate carrier wave. A chromaticity signal is detected. Then, the chromaticity signal is taken out through a so-called take-off transformer 46 having a slope characteristic for correcting the slope characteristic in the video intermediate frequency concentrating filter 44 before and after the color subcarrier frequency. On the other hand, the video intermediate frequency signal is supplied to a second synchronous detector 48 through a second video intermediate frequency concentration filter 47.
7 has a nearly flat characteristic at the video carrier intermediate frequency f _p and the audio carrier intermediate frequency f _s as shown by the curve 2 in the figure, or at the video carrier intermediate frequency f _p and the audio carrier intermediate frequency f s as shown by the broken line 3. The second synchronous detector 48 is synchronized with the _reference carrier having the same frequency and 90° phase shift with respect to the video _intermediate carrier _. The second detector 48 detects the audio intermediate frequency signal.

According to this method, since the audio intermediate carrier wave can be sufficiently attenuated in the filter 44, there is almost no interference with the chromaticity signal of the audio signal.
Furthermore, since so-called 90° synchronous detection is used to detect the audio signal, it is possible to prevent the video signal from being mixed into the audio signal. However, even in this method, harmonics are likely to occur in the first synchronous detector 45,
Similar to the method shown in FIG. 3, this method has the disadvantage of causing cross-color interference due to low-frequency components of the luminance signal. Further, in order to correct the frequency characteristics of the filter 44, a take-off transformer 46 must be provided, which has the disadvantage of complicating the circuit.

In view of the above-mentioned points, the present invention makes it possible to prevent cross-color interference due to low-frequency components of a luminance signal and to simplify the circuit.

FIG. 5 shows a color television receiver according to the present invention, in which the received signal of the antenna 51 is transmitted to the tuner 5.
2 to obtain a video intermediate frequency signal, which is extracted through a preamplifier 53. Then, the video intermediate frequency signal passes through a first video intermediate frequency concentration filter 54, an intermediate frequency amplifier 55 with AGC, and a first wave detector 56.
is supplied to As shown by curve 4 in the figure, the filter 54 has a frequency characteristic that traps or attenuates the audio carrier intermediate frequency _fs and the color subcarrier intermediate wave number _fc , and the first detector 56 detects the luminance signal. be done. Note that the first detector 56
Envelope detection or synchronous detection may be used, but synchronous detection is preferable in terms of performance and ease of circuit integration.

On the other hand, the video intermediate frequency signal is passed through a second video intermediate frequency concentrating filter 57, a wideband intermediate frequency amplifier 58 with AGC, and a second wave detector 5.
9. The filter 57 has a video carrier intermediate frequency f _p , a color subcarrier intermediate frequency f _c , and an audio carrier intermediate frequency f _s as shown by curve 5 in the figure.
When the frequency characteristic is flat and traps the frequency f _p + f _s /2 between the video carrier intermediate frequency f _p and the audio carrier intermediate frequency f _s , or when countermeasures against second-order distortion are taken in the amplifier 58, the broken line As shown in 6, it has a simple flat frequency characteristic without trapping, and the second detector 59 is a synchronous detector, and has the same frequency and phase as 90
Synchronous detection is performed using a standard carrier wave shifted by
The second detector 59 detects the chromaticity signal and the audio intermediate frequency signal. Then, the chromaticity signal is extracted through the audio trap circuit 60, and the audio intermediate frequency signal is extracted through the audio intermediate frequency bandpass filter 61.

FIG. 6 shows an example of the synchronous detector 59 in which a PLL circuit is formed, and the signal from the amplifier 58 is supplied to the multiplier 72 and multiplied by the reference carrier wave from the voltage controlled oscillator 73. , amplifier 58
The signal from the oscillator 73 and the reference carrier wave from the oscillator 73 are supplied to another multiplier 74 for phase comparison, and the error voltage is passed through a low-pass filter 75 to the oscillator 73.
is supplied to the oscillator 73 and its oscillation frequency is controlled so that the reference carrier wave from the oscillator 73 has the same frequency and a phase shift of 90° with respect to the video intermediate carrier wave,
The detected signal from the multiplier 72 is then taken out to an output terminal 77 through a low-pass filter 76.

FIG. 7 shows another example of a synchronous detector 59, in which mutually opposite phase signals obtained at two output terminals of an amplifier 58 are supplied to a multiplier 72, and a capacitor 78 is connected between the two output terminals. A tuning circuit 80 that tunes to the video carrier intermediate frequency is connected through 79, and from both ends of this tuning circuit, reference carrier waves having the same frequency and 90° phase shift with respect to the video intermediate carrier wave are obtained which are opposite in phase to each other. , is supplied to a multiplier 72, and the detected signal from the multiplier 72 is taken out to an output terminal 77 through a low-pass filter 76.

According to this invention, as in the system shown in FIG. 4, so-called 90° synchronous detection is used to detect the audio signal, so that it is possible to prevent the video signal from being mixed into the audio signal.

Furthermore, the present invention has the following remarkable effects compared to the system shown in FIG. That is,
According to this invention, firstly, the second detector 59
Since it is a 90° synchronous detection, the generation of harmonics is suppressed, and therefore the cross color interference caused by the harmonics of the low frequency component of the luminance signal mixed into the chromaticity signal is almost eliminated. Second, the second detector 59 is 90
In synchronous detection, the low-frequency components of the luminance signal are attenuated by the high-pass filter characteristics, making it easier to design a band-pass filter for extracting the chromaticity signal. Third, the second video intermediate frequency concentration filter 5
7 does not have a sloped characteristic before and after the color subcarrier intermediate frequency f _c , so the circuit can be simplified without requiring a take-off transformer for correcting the frequency characteristics as in the method shown in FIG. The phase characteristics of the chromaticity signal are also improved. Fourth, since the first detector 56 does not detect the chromaticity signal, the first video intermediate frequency concentration filter 54 can have a characteristic that sufficiently attenuates the color subcarrier intermediate frequency f _c , and the first When a color subcarrier trap circuit is provided after the detector 56, the attenuation of the trap circuit can be reduced to simplify the trap circuit, and in some cases, the trap circuit itself can be eliminated.

[Brief explanation of the drawing]

FIGS. 1 to 4 are system diagrams of a conventional color television receiver, FIG. 5 is a system diagram of a color television receiver of the present invention, and FIGS. 6 and 7 are system diagrams of the color television receiver of the present invention. It is a connection diagram of an example of a device. 52 is a tuner, 54 and 57 are first and second video intermediate frequency concentration filters, 56 and 5 are
9 is a first and second detector.

Claims (1)

[Claims] 1. A video intermediate frequency signal from a tuner is supplied to a first detector via a first transmission path that has frequency characteristics that are attenuated at a color subcarrier intermediate frequency and an audio carrier intermediate frequency, and The luminance signal is detected by the tuner, and the video intermediate frequency signal from the tuner is transmitted to the second transmission line through a second transmission path having substantially flat frequency characteristics at the video carrier intermediate frequency, the color subcarrier intermediate frequency, and the audio carrier intermediate frequency.
A color television receiver in which chromaticity signals and audio signals are detected by synchronous detection using a reference carrier wave whose phase is shifted by 90 degrees with respect to the video intermediate carrier wave in this second detector.