JPH03186083A - Signal reproducing device - Google Patents

Abstract

PURPOSE:To eliminate cross modulation disturbance in an excellent way by subtracting a voice modulation signal or the like from a demodulated video signal and detecting a remaining 2nd modulation component in an output signal of a subtraction circuit when the cross modulation disturbance is relieved so as to adjust the subtraction level. CONSTITUTION:A reproduction FM signal (a) from an input terminal 1 passes through a high pass filter HPF 7, FM-demodulated at an FM demodulation circuit 2 and a signal (b) is obtained. On the other hand, a band pass filter BPF 4 separates a 2nd modulation wave, i.e. a voice modulation signal (c) or the like from the signal (a), a signal (d) adjusted to an optimum gain by a gain adjustment circuit 5 with information of a detection circuit 6 is subtracted from the demodulation signal (b) by a subtraction circuit 3 and an obtained signal (e) is outputted as a demodulation signal. The detection circuit 6 detects the cross modulation component included in the output signal (e) of the subtraction circuit 3 with the output signal (c) of the BPF 4 accurately to control the gain adjustment circuit 5. Thus, the cross modulation component in existence in the demodulation signal (e) is eliminated in an excellent way.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a signal reproducing device that removes cross-modulation components due to second-order distortion that occur during recording and reproducing of a video disc.

In a conventional video disc system, when playing a video FM signal, the FM modulation wave fc of the H image signal and the audio FM superimposed on the low frequency band are used.
Cross modulation occurs with the modulated wave f+.

In particular, the mixture at due to second-order distortion, fc+fl, is demodulated into the FM demodulated video signal as an interference component of frequency f, significantly deteriorating the reproduced image quality.

Conventionally, various methods have been proposed to remove this cross-modulation component element. Japanese Patent Publication No. 59-29992 discloses that cross-modulation interference can be reduced by subtracting an audio modulation signal from a demodulated video signal.

Moreover, in Japanese Patent Application Laid-open No. 58-203605, there is a reproduction video F.
It is disclosed that cross modulation interference is reduced by further phase modulating the M signal.

Problems to be Solved by the Invention The above-mentioned conventional techniques do not specifically disclose a method for adjusting the subtraction level when removing cross-modulation components.

Furthermore, in reality, the cross-modulation level varies significantly depending on the disc, and even on the same disc, the cross-modulation level varies depending on the outer and inner circumferences, so conventional methods cannot satisfactorily remove cross-modulation, and in some cases, On the contrary, it was possible that cross-modulation interference would increase.

The present invention is based on the above-mentioned problem, and an object of the present invention is to provide a signal reproducing device that can effectively and stably remove cross-modulation interference.

Means for Solving the Problems The present invention modulates a video signal by FM at a carrier frequency fc to form a first modulated wave, and modulates a second signal at a frequency range lower than the frequency fc to form a second modulated wave. , in a signal reproducing device for reproducing from a recording medium on which the first modulated wave and the second modulated wave are mixed and recorded, the first modulated wave is
an FM demodulation circuit that performs Mul@; a first filter that separates the second modulated wave from the reproduced signal; a gain adjustment circuit that adjusts the gain of the output signal of the first filter based on information from the detection circuit; a subtraction circuit for subtracting the output signal of the gain adjustment circuit from the output of the demodulation circuit; A detection circuit for detecting the second modulated wave component remaining in the output signal is provided, and a closed loop is configured to control the gain adjustment circuit using the output of the detection circuit. The second modulated wave component is removed.

As a result, the cross-modulation component present in the flat portion of the video signal in the horizontal or vertical synchronization signal section is detected, and the attenuation level can be adjusted accurately without being disturbed by the video signal itself. Furthermore, since a feedback loop is formed, differences in disks, or even differences in cross-modulation levels depending on the outer and inner circumferences of the same disk, are not a problem.

In addition, instead of processing signals in a high frequency region near the video FM signal fc as seen in Japanese Patent Application Laid-Open No. 58-203605, a low frequency signal is processed by subtracting frequency component 1 from the video FM demodulated signal. Since the processing is as follows, it is much easier to adjust the phase, etc., and stable operation can be achieved.

Embodiment FIG. 1 shows a block diagram of a first embodiment of the present invention, and FIG. 2 shows a signal spectrum corresponding to each part of FIG. 1. The reproduced FM signal a containing third-order distortion input from the input terminal 1 is passed through one bypass filter HPF' to the LflFMt demodulation circuit 21. : r FM demodulated to obtain a signal.

On the other hand, the audio modulation signal C is separated from the signal a by the bandpass filter BPF4, and the signal d, which is adjusted to the optimum gain by the gain adjustment circuit 5 based on the information from the detection circuit 6, is subtracted from the demodulated signal by the subtraction circuit 3. As a result, a signal e is obtained and output as a demodulated signal. Here, the detection circuit 6 is a BPF
4 and the output signal e of the subtraction circuit 3, the cross-modulation component + contained in the signal e is accurately detected, and the gain adjustment circuit 5 is controlled.

Next, a first embodiment of the detection circuit 6 is shown in FIG.

A multiplier 10 multiplies the output of the BPFll which filters the intermodulation frequency component l included in the demodulated output signal e and the signal C which is the output of the BPF4.

Here, the DC component of the output of the multiplier 10 is, for example, the signal C
If the signal e and signal e are in phase, it is positive, if the signal e is out of phase, it is negative, and if there is no signal e l: f r component, it is zero.

A DC component is extracted from the output of the multiplier 10 by an LPF 12. Here, by detecting cross modulation in a section where no video signal of the FMIII signal e exists, detection accuracy can be dramatically improved.

In other words, the horizontal synchronization signal or vertical synchronization signal is separated from the demodulated signal e in the synchronization separation circuit 14, and the LP in that section is
The output of F12 is sampled and held in a sample and hold circuit S/H13.

The sampled and held voltage is the reference potential V r e 1
For example, it is compared with zero in the comparator 15, and outputted to the gain circuit 5 through the LPF 16 so as to increase or decrease the level of the gain adjustment circuit 5 according to the difference.

The gain adjustment circuit 5 is composed of, for example, a multiplier.

Here, the gain adjustment circuit 5 may be controlled by the faint level of the S/H 13; in this case, the comparator]. 5゜LPF16
You can omit it.

As a result, feedback control is performed so that the output of the sample-and-hold circuit 13 is always the same as the reference potential, so that the DC output level of the multiplier 10 is eventually controlled, and the cross-modulation present in the demodulated signal e The component child at can be removed.

Next, a second embodiment of the detection circuit is shown in FIG.

The output signal C of the BPF 4 is input to the inversion circuit 20 and also to the switch circuit 21 . The switch circuit 21 alternately switches the signal C and the output signal of the inverting circuit in one horizontal opening period or one vertical opening period according to an instruction from the timing generating circuit 30, and then outputs the signal to the multiplier 22.

The output signal e of the subtraction circuit 3 is sent to the multiplier 22 after passing through a BPF 23 that filters out the cross-modulation component +. Now, B
When the cross-modulation component element 1 is present in the output of the PF 23, the DC output level of the multiplier 22 has steps of positive and negative levels alternately at each predetermined period. If the cross-modulation component element 1 becomes smaller, the DC step difference also becomes smaller, and when the cross-modulation component is completely removed, the DC step difference also becomes zero. Therefore, feedback control is performed to reduce this DC step to zero ε.

The DC component of the multiplier 22 is taken out by the LPF 24 and sampled and held alternately at predetermined intervals by the sample and hold circuit S/825.26. The potential difference is compared by a comparator 27 and a control signal is output. The control signal is output to the gain adjustment circuit 5 through the LPF 28. The timing generation circuit 30 generates predetermined timing based on the synchronization signal from the synchronization separation circuit 29. Here, the waveforms of each part will be explained using FIG. 5.

It is assumed that the synchronization signal separation circuit 29 separates the vertical synchronization signal from the signal e. However, it may be a horizontal synchronization signal. The timing generation circuit 30 generates pulses P2, P3, and P4 based on the pulse P1 indicating this vertical synchronization signal. In the section A where the cross-modulation level is not removed,
The DC output level of the multiplier 22 has a step at every cycle of P2, and the signal P5. It is P6. P5 (solid line) is a child terminal of the comparator, and P6 (dotted line) is one terminal. As a result, the comparator output becomes P7, and the output of the LPF 28 is controlled to be P8, so that cross modulation is removed.
A stable point indicated by section B will be reached.

In the second embodiment of this detection circuit, since it is possible to absorb characteristic changes due to temperature of each element, extremely stable intermodulation removal can be realized.

In the above-described embodiment, a phase adjustment circuit for adjusting the phase may be inserted before or after the gain adjustment circuit 5. Furthermore, the synchronization separation circuits 14 and 29 may not only separate horizontal or vertical synchronization signals, but also detect periods in which there is no video signal.

Also, the timing pulse from the timing generation circuit is
P3. It is also possible to output the P4 pulse as one bear and detect the cross-modulation component in the vertical synchronization signal section.

Furthermore, the inverting circuit 20 and the switch circuit 21 may be inserted between the BPF 23 and the multiplier 22 to invert the information of the signal e at predetermined intervals.

Further, the second modulated wave component l is not limited to the audio FM signal, and various types such as a color difference FM signal, a low frequency conversion color signal, a pilot signal, and an audio digital signal can be considered.

It goes without saying that the video signal of the first modulated wave includes a number of signals such as a luminance signal, a color difference signal, a high-definition television signal, and a band compression signal.

Effects of the Invention According to the signal reproducing device of the present invention, a video signal is FM-modulated at a carrier frequency fC as a first modulated wave, and a second signal is modulated in a frequency region lower than the frequency fC to generate a second modulation wave. In a signal reproducing apparatus that reproduces a mixture of the 'Jl modulated wave and the second modulated wave from a recorded recording medium, an FMtI modulating circuit ε that FM demodulates the first modulated wave; a first filter that separates the modulated wave;
a gain adjustment circuit that adjusts the gain of the output signal of the first filter based on information from the detection circuit; a subtraction circuit that subtracts the output signal of the gain adjustment circuit from the output of the demodulation circuit; and an output of the subtraction circuit. a detection circuit that receives the signal and the output signal of the first filter and detects the second modulated wave component remaining in the output signal of the subtraction circuit during the horizontal synchronization signal period or the vertical retrace period, the detection circuit By configuring a closed loop that controls the gain adjustment circuit using the output of the subtraction circuit, the second modulated wave component in the FM demodulated signal output from the subtraction circuit is removed. It is possible to accurately adjust the subtraction level without having to detect cross-modulation components present in the flat portion of the video signal and without being affected by interference with the video signal itself.

Furthermore, since a feedback loop is formed, the problem is the difference in the cross-modulation level between the discs, or even between the outer and inner peripheries of the same disc. Furthermore, video FM signal rc
Rather than processing signals in the nearby high frequency range,
Since the process is performed at a low frequency by subtracting the frequency component l from the video F Mlj [ll signal, it is much easier to adjust the phase, etc., and has the extremely large effect of realizing stable operation.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the signal reproducing device of the present invention, FIG. 2 is a spectrum diagram of each part of FIG. 1, and FIG. 3 is a block diagram showing a first embodiment of the detection circuit. FIG. 4 is a block diagram showing a second embodiment of the detection circuit, and FIG. 5 is a waveform diagram of each part of FIG. 4. 2...FM demodulation circuit, 3...Subtraction circuit, 4, 1)゜23...Band pass filter, 5
. . . Gain adjustment circuit, 6 . . . Detection circuit, 10.22 . . . Multiplier, 12.16, 24.
28...Low pass filter, 13.25.26
...Sample hold circuit, 14°29...
... Synchronization separation circuit, 15.27 ... Comparator,
20... Inversion circuit, 21... Switch circuit, 30... Timing generation circuit.

Claims (7)

[Claims] (1) A video signal is FM-modulated at a carrier frequency fc to form a first modulated wave, a second signal is modulated at a frequency range lower than the frequency fc to form a second modulated wave, and the first modulated wave is A signal reproducing device that reproduces a video signal from a recording medium on which the second modulated wave is mixed and recorded, the device comprising: an FM demodulation circuit that FM demodulates the first modulated wave; and a second modulated wave that is separated from the reproduced signal. a gain adjustment circuit that adjusts the gain of the output signal of the first filter using information from a detection circuit; and a subtraction circuit that subtracts the output signal of the gain adjustment circuit from the output of the demodulation circuit. , a detection circuit that receives the output signal of the subtraction circuit and the output signal of the first filter and detects the second modulated wave component remaining in the output signal of the subtraction circuit during the horizontal synchronization signal period or the vertical retrace period. Signal regeneration, characterized in that the second modulated wave component in the FM demodulated signal output from the subtraction circuit is removed by configuring a closed loop that controls the gain adjustment circuit using the output of the detection circuit. Device. (2) The detection circuit includes a second filter that filters a second modulated wave component from the output of the subtraction circuit, a multiplier that multiplies the second filter output and the first filter output, and an output of the multiplier. a sync separation circuit that separates a horizontal or vertical synchronization signal from the output signal of the subtraction circuit; a sample hold circuit that samples and holds the output of the low-pass filter based on information from the sync separation circuit; 2. The signal reproducing apparatus according to claim 1, further comprising a comparator for comparing the output of the sample and hold circuit with a predetermined level, and controlling a gain adjustment circuit based on output information of the comparator. (3) The detection circuit inverts and then multiplies either the second modulated wave component included in the output of the subtraction circuit or the first filter output every predetermined period, and the DC component of the multiplied output is multiplied every predetermined period. Claim 1, characterized in that the gain adjustment circuit is controlled so that the DC output level is constant without fluctuation.
The signal reproducing device described in Section 1. (4) The detection circuit includes a third filter that filters the second modulated wave component from the output of the subtraction circuit, an inversion circuit that inverts the phase of the output signal of the first filter, and an output signal of the first filter. and a switch circuit that selects the output of the inverting circuit at predetermined intervals; a multiplier that multiplies the output of the switch circuit by the output of the third filter; and a first filter that low-pass filters the output of the multiplier. a low-pass filter, two sample-and-hold circuits that alternately sample and hold the output of the first low-pass filter at predetermined intervals, and a comparator that inputs the outputs of the two sample-and-hold circuits to two inputs and compares them; a second low-pass filter for low-pass filtering the output of the comparator; a synchronization separation circuit for separating a horizontal or vertical synchronization signal from the output of the subtraction circuit; and a synchronization separation circuit for controlling the switch circuit and the sample-and-hold circuit. It consists of a timing generation circuit that generates a timing pulse of a predetermined period from the output of the separation circuit, and a second
4. The signal reproducing device according to claim 1, wherein the gain adjustment circuit is controlled by the output of the low-pass filter. (5) The signal reproducing device according to any one of claims 1, 2, 3, and 4, wherein the second modulated wave is an audio signal subjected to FM modulation. (6) The signal reproducing device according to claim 1, wherein the second modulated wave is an FM modulated color difference signal. (7) The signal reproducing device according to claim 1, wherein the second modulated wave is a pilot signal.