JPH035108B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a detection device for detecting video signals and audio signals from television signals.

With conventional detection devices using the intercarrier method, not only does the video signal leak into the audio signal, causing an unpleasant crackling sound in the audio signal, but also the brightness changes from white to black on the TV screen. There is also a problem that the edge part that is used becomes an unknown party. In order to eliminate such drawbacks, it is possible to use a surface acoustic wave filter as a video intermediate frequency filter to separate and extract video carrier components and audio signal components from other signal components, as disclosed in, for example, JP-A No. 51-90520, 51. −90521, 51−93624, 51−93625
It is shown in the official gazette. However, if a surface acoustic wave filter is used to obtain narrow band characteristics for extracting only specific components, the number of electrodes will be enormous, and the dimensions of the surface acoustic wave filter will be very large.

SUMMARY OF THE INVENTION An object of the present invention is to provide a television signal detection device that can easily solve the above problems.

The main point of the present invention is that the above-mentioned problem is solved by the fact that the conventional television signal is of the vestigial sideband type, and that the Nyquist filter required in the intermediate frequency amplification stage is used to separate the upper and lower sidebands. Since the amplitude unbalance occurs, we believe that the cause is that phase modulation has already occurred at the input of the carrier filter, so we separate and extract the video signal component and audio signal component, and extract the video signal component from the audio signal component. By combining and extracting the signal components,
Furthermore, the passband of the filter characteristics for extracting both components is widened, making it easier to realize the characteristics with a surface acoustic wave filter.

The present invention will be explained below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, where 1 is an antenna for receiving a television signal, and 2 is a tuner for converting the received television signal into a video intermediate frequency signal. 3 is a composite surface acoustic wave filter having characteristics as a video intermediate frequency filter, in which a video channel is formed between the input electrode 3A and the output electrode 3B, and has the amplitude characteristics shown in FIG. An audio channel is formed having the amplitude characteristics shown in FIG. In addition,
The frequency characteristics in Figures 2 and 3 are for the Japan channel in the NTSC system, and in these figures, f, fs, fc, fp, and fp are, respectively,
Represents the upper adjacent video trap frequency, audio carrier frequency, color carrier frequency, video carrier frequency, and lower adjacent audio trap frequency. 4 is an amplifier for amplifying the video signal component with the audio carrier component suppressed; 5 is an amplifier for amplifying the composite signal containing the audio signal component and the video carrier component; 6 is a carrier for extracting the video carrier component from the composite signal. Filters 7 and 8 are detectors for multiplying and detecting the video signal and the audio signal using the output of the carrier filter 6, and 9 and 10 are output terminals to which the video signal and the second audio intermediate frequency signal are output.

Since the audio channel in the composite surface acoustic wave filter 3 has the frequency characteristics shown in FIG. The television signal multiplied and detected using the carrier extracted from the output does not suffer from the deterioration in characteristics attributable to the aforementioned causes. Further, the carrier filter 6 is composed of a coil and a capacitor, and the Q of the filter is set to 60, for example, from the viewpoint of stability against fluctuations caused by the tuner station. That is, the characteristics of the carrier filter 6 are made steep, and the resonance frequency fp is made adjustable. This is used for image carrier extraction in filter 3 to prevent the image carrier component from attenuating even if characteristics change due to temperature changes, etc., and to further reduce the number of electrodes when this characteristic is achieved using a surface acoustic wave filter. This is because the peaks are made relatively wide. Furthermore, since the characteristic shown in Figure 3 is bimodal rather than unimodal, its passband is wider than in the case of a single peak. Therefore, the number of electrodes in the surface acoustic wave filter can be further reduced, resulting in a practical size. It is possible to realize a surface acoustic wave filter exhibiting such characteristics.

The present invention not only improves the buzz sound in the audio circuit by about 10 dB compared to the conventional circuit, but also
The sharpness of edges on TV screens has also been improved by approximately 10dB. Buzz sound was evaluated based on the ratio of harmonic components to the audio signal. Further, the sharpness of the edge was evaluated based on the amount of high frequency components generated by multiplying the carrier and the television signal for the conventional case including sidebands and the case of the present invention not including sidebands.

Further, there was no deterioration in image quality due to extracting the carrier from the audio output.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
2 and 3 are amplitude characteristic diagrams of the video channel and audio channel in FIG. 1. 3... Composite surface acoustic wave filter, 6... Carrier filter.

Claims (1)

[Claims] 1. A tuner that converts a received television signal into a video intermediate frequency signal, and a tuner that suppresses other frequency components from the video intermediate frequency signal, including a video carrier component and an audio signal component, compared to these components. A television signal detection device comprising a filter means for extracting a synthesized signal, and an audio intermediate frequency signal generating means for generating an audio intermediate frequency signal from a video carrier component and an audio signal component in the composite signal. . 2 The filter means is a surface acoustic wave filter consisting of a piezoelectric substrate and an input electrode and an output electrode provided on this substrate, and a video intermediate frequency signal is supplied to the input electrode, and a composite signal is extracted from the output electrode. A television signal detection device according to claim 1, characterized in that: 3. A tuner that converts the received television signal into a video intermediate frequency signal, and extracts from the video intermediate frequency signal a composite signal containing a video carrier component and an audio signal component, in which other frequency components are suppressed compared to these components. a filter means for extracting a video carrier component from the composite signal; a first detection means for generating an audio intermediate frequency signal from the video carrier component from the carrier extraction means and the composite signal; 1. A detection device for a television signal, comprising second detection means for generating a video signal from a video carrier component and a video intermediate frequency signal.