JPS643258Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an audio signal processing circuit for television broadcast signals, and uses a resonant circuit to calculate the ratio of the level at each frequency near the video carrier frequency to the audio carrier level of a video intermediate frequency signal from a tuner. An audio signal processing circuit for television broadcast signals that can obtain high-quality audio with a high SN ratio by setting the optimum value for the audio signal processing circuit and supplying it to the video intermediate frequency amplification circuit of the audio signal processing circuit. The purpose is to provide

For example, TV audio multiplex broadcasting in West Germany uses a two-carrier system that uses additional carrier waves, unlike the subcarrier system used in Japan and other countries.
In this two-carrier system, since the frequency of the audio carrier wave of the main channel and the frequency of the additional carrier wave of the sub-channel are close to each other, it is difficult to apply AFC to these audio carrier waves and additional carrier waves.
Therefore, it is difficult to use a separate carrier method as an audio reception method.In general, an intercarrier method is used in which the beat, which is the difference between the video carrier wave and the audio carrier wave, is extracted as an audio intercarrier signal, and the audio is demodulated from this signal. It will be done.

In order to extract high-quality audio in this intercarrier system, the video intermediate frequency signal output from the tuner is split into two, one is supplied to the video processing circuit, and the video intermediate frequency amplifier in the video processing circuit performs band selection (SAW). (by a surface acoustic wave) filter, etc.) and is amplified and processed by video detection, etc., and the other is supplied to the audio signal processing circuit, amplified by the video intermediate frequency amplifier in the audio signal processing circuit, and then subjected to intercarrier detection. Audio intermediate frequency amplification, FM
There is a so-called quasi-parallel system that extracts audio signals by performing wave detection and the like. Here, in a quasi-parallel type television broadcast receiver, the optimal value of the level ratio at each frequency near the video carrier frequency to the audio carrier level of the video intermediate frequency signal in the video signal processing circuit, and the The optimal value of the ratio of the level at each frequency near the video carrier frequency to the audio carrier level of the intermediate frequency signal is different. However, in conventional television broadcasting receivers, the ratio of the level of each frequency near the video carrier frequency to the audio carrier level of the video intermediate frequency signal output by the tuner is set to an optimum value in the video signal processing circuit. Furthermore, in the two-carrier system, since there is a slope in the frequency characteristics near the video carrier frequency p corresponding to the low frequency portion of the video signal, phase distortion may occur and the audio carrier wave may be subjected to cross-modulation. For this reason, there was a drawback that the SN ratio of the audio signal demodulated by the audio signal processing circuit deteriorated.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described below with reference to the drawings.

FIG. 1 shows a block system diagram of an embodiment of a television receiver to which the circuit of the present invention is applied. In the figure, 1 is an antenna, and the radio waves received by the antenna 1 are supplied to the tuner 2, where only the high frequency signal of the desired channel is selected and amplified, and further mixed with the local oscillation frequency signal. The video intermediate frequency signal is converted into a video intermediate frequency signal and outputted from this tuner 2. The video intermediate frequency signal output from the tuner 2 is branched into two, one of which is supplied to the video signal processing circuit 3 and the other to the audio signal processing circuit 4. The ratio of the level of each frequency near the video carrier frequency to the audio carrier level of the video intermediate wave signal is set to an optimal value for the video signal processing circuit 3.

In the video signal processing circuit 3, the video intermediate frequency signal is first subjected to band selection (SAW) in the video intermediate frequency amplification circuit.
After being amplified (by a filter, etc.) and amplified, the video signal is detected, and the video signal and carrier color signal obtained here are amplified or regenerated by a video amplification circuit and a color signal regeneration circuit, respectively, and taken out as three primary color signals by a matrix circuit. It is supplied to the color picture tube 5 along with horizontal and vertical deflection voltages generated from the synchronization signal. As a result, a color image is displayed on the color picture tube 5.

In addition, the buffer amplifier 6 of the audio signal processing circuit 4
The video intermediate frequency signal passed through is supplied to the resonant circuit 7. As shown in FIG. 2A, for example, this resonant circuit 7 is a series resonant circuit consisting of a capacitor C ₁ and an inductance L ₁ , and its terminal 7 a is connected to a buffer amplifier, and its terminal 7 b is connected to a video intermediate frequency amplification circuit 8 . It is provided in parallel to the signal transmission path. The buffer amplifier 6 is provided so that the resonance circuit 7 does not affect the video intermediate frequency signal supplied to the video signal processing circuit 3. Here, when the video carrier wave and the audio carrier wave of the video intermediate frequency signal output from the tuner 2 have a level ratio as shown by the arrows in FIG. 2B, the resonant frequency of the resonant circuit is as shown by the broken line in FIG. 2B. As shown, the frequency is between the video carrier frequency p and the audio carrier frequency s. By changing the inductance _L1 and moving this resonance frequency toward the frequency p side, for example, the video carrier wave level is attenuated, and the ratio of the level at each frequency near the video carrier frequency to the audio carrier level of the video intermediate frequency signal is The optimum value is set for the video intermediate frequency amplification circuit 8 to the audio detection circuit 11 of the audio signal processing circuit 4. By setting in this manner, at the same time, the frequency characteristics near the video carrier frequency p corresponding to the low frequency portion of the video signal are corrected so as to become flat due to the slope portion of the frequency characteristics of the resonant circuit.

The video intermediate frequency signal outputted from this resonance circuit 7 is band-selected (SAW) by a video intermediate frequency amplification circuit 8.
After being amplified by an intercarrier detection circuit 9, a beat, which is the difference between the video carrier wave and the audio carrier wave, is extracted as an intercarrier signal. This intercarrier signal is amplified by an audio intermediate frequency amplification circuit 10, and then subjected to FM detection by an audio detection circuit 11 to demodulate the audio signal.
This audio signal is amplified by an amplifier circuit 12 and then supplied to a speaker 13, from which a sound is produced.

In this way, the video intermediate frequency signal supplied from the tuner 2 and having the ratio of the level at each frequency near the video carrier frequency to the audio carrier level optimized for the video signal processing circuit 3 is converted to the audio carrier by the resonance circuit 7. Since the ratio of the level to the level at each frequency near the video carrier frequency is set to an optimal value for the video intermediate frequency amplification circuit 8 to the audio detection circuit 11, the audio signal output from the audio signal processing circuit 4 is the same as the video signal. SN without being affected
ratio becomes higher. In addition, the resonant circuit 7 suppresses the low-frequency components of the video signal close to the video carrier frequency p in FIG. Mixing of the video signal with the audio signal is prevented, and a high quality audio signal can be obtained.

As mentioned above, the audio signal processing circuit for television broadcast signals according to the present invention converts the video intermediate frequency signal having two audio carrier waves output from the tuner into the video signal processing circuit provided in the video signal processing circuit and the audio signal processing circuit respectively. In an audio signal processing circuit for an intercarrier television broadcast signal that is supplied to an intermediate frequency amplification circuit, a video intermediate frequency signal from a tuner is supplied, and each frequency near the video carrier frequency with respect to the audio carrier level of the video intermediate frequency signal is Since it is equipped with a resonant circuit that sets the level ratio to an optimal value for the audio signal processing circuit and supplies it to the video intermediate frequency amplification circuit of the audio signal processing circuit, the audio signal output from the audio signal processing circuit is a video signal. The signal-to-noise ratio is high without being affected by the noise, and the resonant circuit suppresses the low-frequency components of the video signal that are close to the video carrier wave, so the video signal is not mixed into the audio signal after audio detection and a high-quality audio signal is obtained. It has the following features:

[Brief explanation of the drawing]

Fig. 1 is a block system diagram of an embodiment of a television receiver to which the circuit of the present invention is applied, Fig. 2A is a circuit diagram of a part of the circuit shown in Fig. 1, and Fig. 2B is a video carrier wave and an audio carrier wave. FIG. 3 is a diagram showing the level and frequency characteristics of the resonant circuit. 2...Tuner, 3...Video signal processing circuit, 4
...Audio signal processing circuit, 6...Buffer amplifier,
7... Resonance circuit, 8... Video intermediate frequency amplification circuit,
9... Intercarrier detection circuit, 10... Audio intermediate frequency amplification circuit.

Claims (1)

[Scope of utility model registration request] Audio signal processing of an intercarrier television broadcast signal that supplies a video intermediate frequency signal with two audio carrier waves output from a tuner to a video intermediate frequency amplification circuit provided in each of the video signal processing circuit and the audio signal processing circuit. The circuit receives the video intermediate frequency signal from the tuner and sets the ratio of the level of each frequency near the video carrier frequency to the audio carrier level of the video intermediate frequency signal to an optimal value for the audio signal processing circuit. An audio signal processing circuit for television broadcast signals, comprising a resonant circuit that supplies a video intermediate frequency amplification circuit of the audio signal processing circuit.