JPH02241283A - Disk reproducing device - Google Patents

Abstract

PURPOSE:To remove the influence of jitter from a reproduced sound signal by separating and demodulating a sound signal being frequency-modulated, from the reproduced signal by a second demodulating means to output the reproduced sound signal, and adding the output of a frequency detecting means to the reproduced sound signal by a suitable ratio in an adding means. CONSTITUTION:The horizontal synchronizing signal of a reproduced video signal or a clock signal, of which a phase is synchronized to a burst signal, is outputted from a frequency converting means 7. A frequency detecting means 9 outputs a signal corresponding to the oscillating frequency of a variable frequency oscillating means 5 and executes almost reverse operation to the oscillating means 5. As a result, a signal to be almost proportional to the input of the variable frequency oscillating means 5 is obtained as the output of the frequency detecting means 9. In an adding means 11, the output of the frequency detecting means 9 is added to the reproduced sound signal, which is obtained by the second demodulating means, by the suitable rate and a noise component caused by the jitter is offset from the reproduced sound signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a disc playback device for playing back signals from a disc on which frequency-modulated video and audio signals are recorded.

Conventional technology When reproducing signals from a disc on which frequency-modulated video and audio signals have been recorded, playback is generally accompanied by fluctuations in the time axis that were not present in the recorded signal due to eccentricity or mechanical vibration of the disc. The signal is played. If there is such a fluctuation (jitter) in the time axis in the reproduced signal, the effect will be a direct synchronization disturbance with respect to the video signal, and at the same time, if the video signal is a composite signal, it will appear as color unevenness. On the other hand, since the jitter frequency component of the audio signal is demodulated together with the audio signal, the disk rotation frequency and its harmonic components are mixed into the reproduced audio, resulting in harsh noise. For this reason, this type of disc playback device has been devised to suppress the above-mentioned adverse effects. This will be explained below with reference to FIG. FIG. 4 shows a block diagram of an example of a conventional disc playback device. The reproduced signal read from the disk by the reproducing means 1 is separated into video signal bands by the first demodulating means 2, subjected to FM demodulation, and outputted as a reproduced video signal. The phase comparison means 3, the loop filter 4, the clock generation means 12, and the frequency division means 8 constitute a phase-locked loop (PLL), which generates a clock signal that is phase-synchronized with the horizontal synchronization signal or burst signal of the reproduced video signal. Occur. Jitter is removed from the reproduced video signal by writing the reproduced video signal into the digital memory 13 in synchronization with this clock signal and reading it out using a stable clock with no time axis fluctuation obtained by the reference clock oscillator 14. On the other hand, the second demodulation means 10 separates the audio signal band from the reproduced signal, performs FM demodulation, and outputs the reproduced audio signal, but as mentioned earlier, this reproduced audio signal contains noise components due to jitter. . On the other hand, at the input of the clock generating means 12, a frequency fluctuation component of the reproduced signal, that is, a signal approximately equivalent to a noise component in the reproduced audio signal appears. Therefore, this noise component is canceled out by adding an appropriate gain to this in addition means 11 and adding it to the reproduced audio signal. In this way, the influence of jitter is also removed from the reproduced audio signal (for example,
121386, etc.).

Problems to be Solved by the Invention Signal processing circuits in disc playback devices tend to be digitized in order to improve performance and reliability and reduce costs, but when the video processing circuit in the above configuration is digitized, The following problems arise. That is, the input signal of the clock generation means is a digital value, but in order to add this to the audio signal, a D/A converter is required to convert it into an analog value. Considering converting a digital video processing circuit into an LSI, including the D/A converter within the LSI will increase the chip area, and if it is attached externally, the number of terminals for connection will increase and the number of components will also increase. In any case, this increases the hardware scale and increases costs.

Means for Solving the Problems In order to solve the above problems, the disc playback device of the present invention reads signals from a disc on which video signals and audio signals are frequency-modulated and synthesized, respectively, and outputs a playback signal. means, first demodulating means for separating and demodulating a frequency-modulated video signal from the reproduced signal and outputting a reproduced video signal; a phase comparison means for comparing and outputting a phase difference signal; a loop filter for correcting the frequency phase characteristic of the phase difference signal; and a variable frequency oscillation means for generating a signal with a frequency based on the output of the loop filter; a signal generation means for generating a frequency reference signal; a frequency conversion means for performing frequency addition of the output of the variable frequency oscillation means and the reference signal and outputting the addition result as a clock signal; and a frequency conversion means for frequency-dividing the clock signal. frequency dividing means for generating the internal synchronization signal and supplying it to the phase difference detection means; frequency detection means for outputting a signal corresponding to the frequency of the output signal of the variable frequency oscillation means; The second demodulating means separates and demodulates the reproduced audio signal and outputs the reproduced audio signal, and the adding means adds the output of the frequency detecting means and the reproduced audio signal at an appropriate ratio.

Effect of the Invention With the above-described configuration, the present invention can connect the video processing circuit and the audio processing circuit with the addition of a small amount of hardware, and remove the influence of jitter from the reproduced audio signal.

Embodiment Hereinafter, a disc reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of a disc playback device according to an embodiment of the present invention, in which 5 is variable frequency oscillation means, 6 is signal generation means, 7 is frequency conversion means, and 9 is frequency detection means. . Moreover, the reproduction means 1,
First demodulation means 2, phase comparison means 3, loop filter 4
, the frequency dividing means 8, the second demodulating means 10, and the adding means 11 are the same as those shown in FIG. A signal is reproduced from the disk in the reproduction means 1, and the first demodulation means 2
The operation until a reproduced video signal is obtained is the same as that shown in FIG. phase comparison means 3, loop filter 4, variable frequency oscillation means 5, signal generation means 6, frequency conversion means 7,
The frequency dividing means 8 constitutes a phase locked loop. This too,
Compared to FIG. 4, the operation as a loop is the same except that the clock generation means 12 is replaced with the variable frequency oscillation means 5, the signal generation means 6, and the frequency conversion means 7, and the frequency conversion means 7 A clock signal whose phase is synchronized with the horizontal synchronization signal or burst signal of the reproduced video signal is output. Although omitted in the first session, jitter can be removed from the reproduced video signal by using a digital memory and a reference clock oscillator as in FIG. 4. The frequency detection means 9 outputs a signal corresponding to the oscillation frequency of the variable frequency oscillation means 5, and operates almost in the opposite direction to that of the variable frequency oscillation means 5. As a result, a signal substantially proportional to the input of the variable frequency oscillation means 5 is obtained as the output of the frequency detection means 9. In the adding means 11, the output of the frequency detecting means 9 is added to the reproduced audio signal obtained by the second demodulating means at an appropriate ratio, and the part where the noise component due to jitter is canceled out from the reproduced audio signal is added to the reproduced audio signal obtained by the second demodulating means. 4
It is similar to the figure.

FIG. 2 shows a specific embodiment of the frequency conversion means 7, in which 15 is an exclusive OR (EX-OR) gate and 16 is a band pass filter. Binary signals from the signal generation means 6 and the variable frequency oscillation means 5 are input to the EX-OR gate 15. Since the exclusive OR operation is a multiplication in which the input signal is regarded as a binary signal of (1, -1), beat components of each input frequency appear in the output. The bandpass filter 16 extracts only the necessary components, for example, the sum component of the fundamental frequencies of each input, from these beat components. With this configuration, if the output frequency of the variable frequency oscillation means 5 is changed, the output frequency of the bandpass filter 16 will also change accordingly, but its value is offset by the output frequency of the signal generation means 6. If the frequency center value of the clock signal to be finally generated is relatively high and the frequency fluctuation width is sufficiently small compared to the center value, the output frequency of the signal generating means 6 should be made sufficiently close to this frequency center value. ,
Since the output frequency of the variable frequency oscillation means 5 is relatively low and can be varied over a wide range, implementation using a digital circuit is easy. In this example, an EX-OR gate is used as the gate means, but the present invention is not limited to this, and an AND gate, an OR gate, another gate, or simply an analog switch may be used. Furthermore, the bandpass filter 16 needs to sufficiently attenuate adjacent unnecessary beat components in order to suppress jitter in the output signal, and can be configured with a filter with relatively steep characteristics, such as a ceramic filter, for example. .

FIG. 3 shows a specific example of the configuration of the frequency detection means 9, in which 17 is a mono multi-vibration brake and 18 is a low-pass filter. The mono multi-by-break 17 receives the output of the variable frequency oscillation means 5 and outputs a C) Lt pulse of a constant width in synchronization with the edge thereof, for example, the rising edge. The output pulse width of the mono-multi-bi-break 17 is in this case selected to be smaller than the minimum value of the output signal period of the variable frequency oscillation means 5.

The low-pass filter 18 smoothes this pulse signal and removes the pull component. As a result, a signal approximately proportional to the oscillation frequency of the variable frequency oscillation means 5 is obtained at the output of the low-pass filter 18. Note that since the frequency of the variable frequency oscillation means 5 can be selected to be relatively low and sufficiently higher than the audio band, the mono multi-vibration break 17 can be easily constructed using a counter, and the low-pass filter can be constructed using a simple For example, a filter based on R-C may be used.

Note that although a configuration using a monomultipipe rake as the frequency conversion means is shown here, the configuration is limited to any device that receives the output of the variable frequency oscillation means and outputs a signal according to the frequency. isn't it.

Effects of the Invention As described above, according to the present invention, even when a video signal system is digitized, the effect of jitter can be removed from reproduced audio by connecting it to an audio processing circuit with a small addition of hardware. It is possible to realize a disc playback device suitable for.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a disc playback device according to the present invention, FIG. 2 is a configuration diagram of an example of frequency conversion means, FIG. 3 is a configuration diagram of an example of frequency detection means, and FIG.
The figure is a block diagram showing the configuration of a conventional disc playback device. DESCRIPTION OF SYMBOLS 1... Reproduction means, 2... First demodulation means, 3... Phase comparison means, 4... Loop filter, 5...・Variable frequency oscillation means, 6.
... Signal generation means, 7 ... Frequency conversion means, 8 ... Frequency division means, 9 ... Frequency detection means, 10 ...... Number Second demodulation means, 11...
...addition means.

Claims (2)

[Claims] (1) A reproduction means that reads signals from a disc on which video signals and audio signals are frequency-modulated and synthesized and recorded and outputs a reproduction signal, and a reproduction unit that separates and demodulates the frequency-modulated video signal from the reproduction signal and reproduces a video image. a first demodulation means for outputting a signal; a phase comparison means for comparing the phases of the horizontal synchronization signal or burst signal of the reproduced video signal and the internal synchronization signal and outputting a phase difference signal; and a phase comparison means for outputting a phase difference signal; a loop filter for correcting phase characteristics; a variable frequency oscillation means for generating a signal with a frequency based on the output of the loop filter; a signal generation means for generating a reference signal of a specific frequency; and an output of the variable frequency oscillation means. a frequency converter that performs frequency addition with the reference signal and outputs the addition result as a clock signal; a frequency divider that divides the frequency of the clock signal to generate the internal synchronization signal and supplies it to the phase difference detection means; a frequency detection means for outputting a signal corresponding to the frequency of the output signal of the variable frequency oscillation means; a second demodulation means for separating and demodulating the frequency-modulated audio signal from the reproduction signal and outputting the reproduction audio signal; A disk reproducing apparatus characterized by comprising an adding means for adding the output of the frequency detecting means and the reproduced audio signal at an appropriate ratio. (2) The frequency conversion means includes gate means for performing a logical AND or exclusive OR operation between the output of the variable frequency oscillation means and the reference signal, and a signal in a specific frequency domain from the output of the gate means. 2. The disc playback device according to claim 1, further comprising a band pass filter for extracting the.