JPH03184481A - Television receiver - Google Patents

Abstract

PURPOSE:To reduce sound buzz by operating a phase detector at a circuit, which executes PLL phase shift detection, only during a synchronizing signal period by using a switch circuit, holding the phase detection output during a picture period excepting for the synchronizing signal period by using a hold circuit and supplying the output to a VCO. CONSTITUTION:A phase detector 7 is turned ON only during the synchronizing signal period by a switch circuit 12 and supplies the phase detection output to a hold circuit 13. The hold circuit 13 holds the phase detection output for the above mentioned synchronizing signal period while the phase detector 7 is turned OFF, namely, during the picture period. A VCO 8 is controlled by the output of this hold circuit 13. Thus, the output frequency of the VCO 8 is stably fixed to a video intermediate frequency without being affected by the signal of the picture period. For the output from an amplifier 5, phase detection is executed by a phase detector 10 with a signal shifted at 90 deg., and the output is converted to a sound intermediate frequency signal. Therefore, the buzz can be prevented form being generated in the sound output and the sound can be obtained with high quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Objective of the Invention J (Field of Industrial Application)] The present invention relates to a television receiver for obtaining high-quality audio using a separate audio detection method.

(Prior Art) In recent years, there has been a demand for high quality sound not only for video but also for audio in television receivers. Under these circumstances, the number of recent television receivers that use a separate audio detection method is increasing. This method supplies the video intermediate frequency component to a phase locked loop (hereinafter referred to as PLL), locks the oscillation frequency of the voltage controlled oscillator in the PLL to the video intermediate frequency, and uses the CO output to detect the audio intermediate frequency. This is what we do.

FIG. 2 shows a block diagram of a television receiver using a conventional separate audio detection method. A television signal received by an antenna 1 is converted to an intermediate frequency by a tuner 2, and this intermediate frequency signal is separated into a video component and an audio component by an input filter 3, and each is amplified by amplifiers 4 and 5. Ru. FIG. 3 shows the frequency characteristics of the outputs (a) and (b) of the input filter 3. In Figure 3, P is a video carrier (58, 75
M1''z), C is the color subcarrier (55, 17
M1-1 z), S is the voice main 11 rear (54, 25
MHz>. The video component from the amplifier 4 is divided into two parts, one of which is subjected to phase detection (Kakefeng detection) with an in-phase signal from a vcos, which will be described later, in a phase detector 7 and demodulated into a video signal. The other one is phase-detected in the phase detector 7 with a signal obtained by phase-shifting the output signal of the vCO8 through a 90" phase shift circuit 9, and the detected output is used as a control signal for the vC
A PLL circuit is added to VCO8 so that the frequency of the output signal of vCO8 becomes the video intermediate frequency (58, 75 MHz). Note that the 90° phase shift circuit 9
is inserted to correct a 90'' phase shift caused by the PLL circuit and to match the phase of the input video component and the CO output signal.

The output from the amplifier 5 is converted to vcos by the phase detector 10.
The signal is phase-shifted by 90'' and converted into an audio intermediate frequency signal (4.5 MHz).The audio intermediate frequency signal is further demodulated into an audio signal by the FM detector 11.

According to the above configuration, the audio component is separated from the video component,
Since the signals are amplified and detected independently, they are not easily affected by video components, and noise such as buzz can be significantly reduced.

However, in reality, the control signal for vCO8 is obtained from the video component, so fluctuations in this control signal cause the CO frequency to fluctuate, resulting in audio being output as M detection output.Especially when high modulation is used, the video component As the carrier level decreases, the detection efficiency of the phase detector 7 decreases, and it is easily affected by the output offset of the vCO 8, causing frequency fluctuations.As a result, the frequency of the voice intermediate frequency signal fluctuates, causing audio buzz. There was a problem.

(Problems to be Solved by the Invention) As described above, in the conventional circuit, the output frequency of the vCO fluctuates due to fluctuations in the video component, so the audio intermediate frequency phase-detected using the VCO frequency also fluctuates, causing audio buzz. There was a problem that occurred.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a television receiver that can eliminate such CO frequency fluctuations due to video components, stabilize the audio intermediate frequency, and eliminate audio buzz.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a television receiver using a separate audio detection method, in which a phase detector in a circuit that performs PLL phase detection is controlled by using a switch circuit to control the synchronization signal period. The phase detection output is held in a video period other than the synchronization signal period using a hold circuit, and is supplied to the vCO.

(Function) According to the present invention, since vCO is controlled during the synchronization signal period in which the carrier level of the video component is stable, it is not affected by the decrease in phase detection efficiency in the highly modulated portion of the video period or the cross-modulation of the video component. First, since the vCO oscillation frequency is stabilized, audio buzz caused by video components can be significantly reduced.

(Example) Examples will be described with reference to the drawings.

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

In this figure, the same parts as in FIG. 2 are given the same reference numerals. That is, antenna 1, tuner 2, filter 3, amplifier 4.5, phase detector 6,7°10, VCO8,90
``The phase shift circuit 9 and the FM detector 11 are the same as in FIG. 2.The difference from FIG. 2 is that the phase shift circuit 9 and the FM detector 11 are the same as in FIG. While a switch circuit 12 is provided, a hold circuit 13 is provided to hold the output of the phase detector 7, and a gate pulse corresponding to the synchronization signal period of the television signal is sent from a terminal 14 to these sample and hold circuits 12 and 13. is supplied to control the on period of the switch circuit 12 and the hold period of the hold circuit 13. That is, the switch circuit 1
2 operates to turn on the phase detector 7 during the synchronization signal period, and the bold circuit 13 (operates to hold the phase detection output of the main circuit during the video period other than the synchronization signal period). Shimutatsu, circuit 12.13 is terminal 14
It constitutes a sample-and-hold circuit that performs sampling and bold operations in response to control signals from the circuit. The other configurations are the same as in FIG. 2.

In the configuration shown in FIG. 1, a television signal received by an antenna 1 is converted to an intermediate frequency by a tuner 2, and the intermediate frequency signal is separated into a video component and an audio component by an input filter 3, and each is divided into a video component and an audio component by amplifiers 4 and 5. amplified. The output of the amplifier 4 is phase-detected (multiplicatively detected) with the output of the VCO 8 in a phase detector 6, and demodulated into a video signal. Further, the output of the amplifier 4 is outputted to the phase detector 7 by vc
The phase detector 7 is turned on only during the synchronization signal period by the switch circuit 12, and its phase detection output is supplied to the hold circuit 13.The hold circuit 13 is configured as described above. The phase detection output of the synchronization signal period is held during the period when the phase detector 7 is off (i.e., the video period).This bold circuit 1
By controlling VC○8 with the output of 3, vco
The output frequency of s is affected by the signal in the video period (and is stably fixed at the video intermediate frequency).

Then, the output from the amplifier 5 is phase-detected with a 90" phase-shifted signal in a phase detector 10, and converted into an audio intermediate frequency signal (4,5M1lz).Furthermore,
This audio intermediate frequency signal is demodulated into an audio signal by the FM detector 11.

According to this embodiment, the frequency of the VCO 8 output, which serves as a reference signal in the phase detector 10 for performing separate audio detection, is determined in the synchronization signal period with little fluctuation. That is, since the frequency is fixed during the video period, which is susceptible to the effects of a decrease in the detection efficiency of the phase detector 7 due to a decrease in the carrier level during high modulation, and the effects of cross-modulation of the video signal, the vcos frequency is It is not subject to fluctuations due to the signal during the video period. Therefore, it is possible to suppress the buzz signal that conventionally appears in the FM detection output due to the fluctuation in the audio intermediate frequency as a result of the frequency fluctuation in the video period, and it is possible to obtain high-quality audio.

[Effects of the Invention] As described above, according to the present invention, 90
It is possible to eliminate zero frequency fluctuations, stabilize the audio intermediate frequency, prevent buzz from occurring in the audio output, and obtain high-quality audio.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a television receiver according to an embodiment of the present invention, FIG. 2 is a block diagram showing a conventional television receiver, and FIG. 3 is a block diagram showing a video component and an audio component separated by an input filter. FIG. 2 is an explanatory diagram showing the frequency characteristics of 3... Input filter, 4, 5... Amplifier, 7.10
...Phase detector, 8...Voltage controlled oscillator, 12...
・Switch circuit, 13...Hold circuit, 14...
Gate signal input terminal.

Claims (1)

[Scope of Claims] A filter that separates a television signal converted into an intermediate frequency into an audio component and a video component, a first amplifier that amplifies the video component from the filter, and a first amplifier that amplifies the video component from the filter. a second amplifier for amplification, a phase detector, and a voltage controlled oscillator, the video component from the first amplifier and the output of the voltage controlled oscillator are phase detected by the phase detector, and the phase detected output is obtained. a PLL circuit that inputs the signal as a control signal to the voltage controlled oscillator to match the output frequency of the voltage controlled oscillator with the frequency of the video carrier component from the first amplifier; a holding circuit provided in the PLL circuit to hold the output of the phase detector during the video period when the phase detector is off and supply it to the voltage controlled oscillator; , A television receiver comprising phase detection means for phase detecting the audio component from the second amplifier and the output of the voltage controlled oscillator of the PLL circuit to obtain an audio intermediate frequency signal.