JPH087932B2 - Signal detector - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal detection device used for detecting a single frequency signal in a reproduction signal of a disc.

2. Description of the Related Art In a certain type of video disc, a signal of a single frequency, that is, a pilot carrier is superposed on a video signal for recording in order to obtain a signal synchronized with the rotation of the disc during reproduction. This pilot carrier is extracted from the reproduction signal of the disc by a bandpass filter and used for reproduction of a clock synchronized with the reproduction video signal. The reproduced clock is used for controlling the rotation of the spindle motor and correcting the time axis of the video signal. The detection of whether or not the pilot carrier is extracted is generally made by the amplitude of the extracted signal.

In the disc playback device, when the disc starts to rotate,
During special playback such as variable speed playback or track jump, there is a transitional state where the rotation of the disk is not stable. Therefore, the frequency distribution of the reproduced signal is not always in the normal state. In the signal extraction circuit using the bandpass filter, in the above state, signals and noise components different from the pilot carrier to be originally extracted pass through the band of the bandpass filter. Therefore, there is a problem that a wrong signal is extracted and a portion using the signal malfunctions. Therefore, it becomes necessary to switch the control using a means for detecting whether or not the extracted signal is the signal to be originally extracted.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, the conventional signal detection device that determines the signal extraction based on the signal amplitude cannot detect the signal or noise component that should not be detected as described above, and thus cannot be used.

The present invention has been made in view of the above problems, and correctly detects whether or not a single-frequency signal reproduced from a disc has been extracted, including when the reproduction signal of the disc is not in a normal state. It is an object of the present invention to provide a signal detection device that can be used.

Means for Solving the Problems In order to solve the above problems, the present invention provides a signal including a bandpass filter for extracting a signal and a limiter for converting the signal extracted by the bandpass filter into a rectangular wave. An apparatus for determining an extraction signal of an extraction circuit, comprising: a first cycle comparison circuit and a first cycle comparison circuit for detecting a signal having a longer cycle than a cycle of a regular extraction signal from the extraction signals of the signal extraction circuit. A second period comparison circuit for detecting whether or not the detection signal of the circuit is output during one or more periods of the longest period signal that can be extracted by the signal extraction circuit.

Operation In the above-described configuration, the signal near the center frequency of the bandpass filter is extracted from the reproduction signal of the disc, and the signal is converted into a rectangular wave by the limiter. When a single-frequency signal is correctly extracted, the signal-to-noise ratio is large, and the periodic fluctuation of the signal falls within the range of the rotational jitter component of the disc. On the other hand, when another signal or noise is extracted, it contains a signal component with a period shorter or longer than the period of the signal to be originally extracted.

The first period comparison circuit detects a signal having a period which is not included in the single frequency signal to be extracted, and when this is frequently detected, it is another signal. Therefore, if the detection signal is not detected for a certain period in the second period comparison circuit, it can be determined that the target single frequency signal is extracted.

Embodiment Hereinafter, the configuration and operation of the signal detection device according to an embodiment of the present invention will be described.

In this embodiment, a signal of a single frequency, that is, a pilot carrier is frequency-multiplexed in the lower band of the lower sideband of the recorded video signal, and a reproduction signal of a video disc in which a PCM audio signal is frequency-multiplexed in the lower band is used. Think FIG. 2 is a frequency distribution diagram of this reproduction signal.

In the overall configuration of the device shown in FIG. 1, a signal passing through the band of the bandpass filter 1 is extracted from the reproduction signal of the disc. The extracted signal is converted into a limiter 2 rectangular wave. The bandpass filter 1 can pass signals in the band other than the pilot carrier that should be originally passed, so that some kind of extracted signal is always output from the limiter 2.

FIGS. 3A to 3D are signal waveform diagrams showing the characteristics of the extracted signal of the signal extraction circuit including the bandpass filter 1 and the limiter 2. Here, t0 represents the central period of the pilot carrier, and the widths of the rising and falling portions of the waveform represent jitter, that is, the period fluctuation of the signal.

When the disc is rotating at the regular rotation speed, the pilot carrier passes through the center of the band of the bandpass filter 1 and is extracted. Therefore, the extracted signal has a large signal-to-noise ratio and less noise. This signal is converted into a rectangular wave by the limiter 2, and the output signal of the limiter 2 has the minimum period fluctuation except for the jitter component generated by the rotation of the disk (Fig. 3 (a)). On the other hand, when the rotation of the disc is slightly deviated, the pilot carrier can be extracted, but since the center frequency of the bandpass filter 1 is deviated, the extracted signal contains a lot of noise and its period fluctuates (rotation). Fig. 3 (b)
Fig. 3 (c) when it is a little faster. Further, when the rotation of the disc is significantly deviated, the video signal having a frequency higher than that of the pilot carrier and other signals such as the PCM signal multiplexed in the low frequency pass through the bandpass filter 1, so that the cycle of the extraction signal is It varies within the band of the bandpass filter 1 and is unstable (Fig. 3 (d)).

As described above, based on the characteristics of the signals extracted by the bandpass filter 1 and the limiter 2, whether the pilot carrier is correctly extracted by using the first period comparison circuit 3 and the second period comparison circuit 4 is determined. Can be detected.

The period comparison circuit of this embodiment will be described. FIG. 4 shows a period comparison circuit when a retriggerable mono-multi is used. The first mono-multi 3 detects when a signal having a period longer than the time constant t1 is input. The second mono-multi 4 detects this when the detection signal of the first mono-multi 3 is not output during the time constant t2.

Here, the time constant t1 is set slightly larger than the longest period of the correctly extracted pilot carrier, and the time constant t2 is set sufficiently larger than the maximum period of the signal that can pass through the bandpass filter 1. Then, the first mono-multi 3
At, a signal that is not a pilot carrier is detected, and it is confirmed that the second mono-multi 4 does not exist for a certain period.

This will be described with reference to the signal waveform diagrams of FIGS. 5 (a) to 5 (f). FIG. 7A shows the extracted signal waveform of the correctly extracted pilot carrier. FIG. 11B shows the output waveform of the first mono-multi 3 triggered by the rising edge of FIG. Since the waveform of the correctly extracted pilot carrier is always shorter than the period t1, the output waveform of the first mono-multi 3 (FIG. 9B) remains triggered and remains at the high level. FIG. 7C shows the output waveform of the second mono-multi 4 triggered by the rising edge of FIG. In the second mono-multi 4, if the rising edge of FIG. 7B is not detected within the period of t2,
Become high level. In the case where the input is (a) in the figure, (b) is always at the high level, and (c) is always at the high level after t2, and it is determined that the pilot carrier is extracted.

Next, FIG. 5 (d) is an example of an extracted signal waveform other than the pilot carrier. (E) is the output waveform of the first mono-multi 3 triggered by the rising edge of (d). Period for extracted signals other than pilot carrier
A signal component with a period longer than t1 is detected and goes low. (F) is the output waveform of the second monomulti 4 triggered by the rising edge of (e). The second monomulti 4 detects the rising edge of (e) within the period of t2,
(F) becomes low level. That is, when the input is (d), it is determined that the detection signal appears in (e), (f) remains low level, and the pilot carrier is not extracted.

With the above configuration and operation, the extracted signal is
It is detected that the disk is the pilot carrier extracted at the time of normal rotation.

In the above embodiment, an asynchronous circuit using monomulti as the period comparison circuit has been taken as an example, but it is clear that a similar period comparison circuit can be realized by a synchronous circuit using a counter.

EFFECTS OF THE INVENTION According to the present invention, it is possible to detect with a simple configuration whether or not the signal extracted from the reproduction signal of the disc by the bandpass filter and the limiter is a signal of a single frequency that is originally required.

Therefore, the malfunction can be eliminated by using it as the control switching signal of the motor or the memory of the disc reproducing apparatus.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a signal detecting device according to an embodiment of the present invention, FIG. 2 is a frequency distribution diagram of a reproduction signal of a disc in this embodiment, and FIGS. 3 (a) to 3 (d) are books. FIG. 4 is a signal waveform diagram showing an extracted signal in the embodiment, FIG. 4 is a configuration diagram of a period comparison circuit in the embodiment, and FIG.
(F) is a signal waveform diagram showing a detection signal in the present embodiment. 1 ... band pass filter, 2 ... limiter, 3 ... first period comparison circuit, 4 ... second period comparison circuit.

Claims (1)

[Claims] 1. An apparatus for discriminating an extracted signal of a signal extraction circuit, which comprises a bandpass filter for extracting a signal and a limiter for converting the signal extracted by the bandpass filter into a rectangular wave, A first period comparison circuit that detects a signal having a longer period than the period of the regular extraction signal and a detection signal of the first period comparison circuit are extracted from the extracted signals of the signal extraction circuit by the previous period signal extraction circuit. And a second period comparison circuit for detecting whether or not the longest period signal to be obtained is output during one period or more.