JPS6242347B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a recorded information presence/absence identification device for detecting the presence or absence of recorded information on a recording disk.

If information is recorded on only one side of a video disc, if you attach the non-information recording side to the playback device and start playback, not only will you not be able to get any recorded information from the pickup. Because control signals for the spindle servo, tangential servo, tracking servo, and focus servo for controlling the rotation of the disk, the tracking servo, and focus servo for controlling the movement of the pick-up cannot be obtained, each servo system does not operate. There is a risk of it going out of control. In addition, end detection is required to detect the end of the recording track on the disc and automatically end playback.

For this reason, identification of the presence or absence of recorded information is essential for disc playback devices, and high reliability is required. There is a method of using a detection signal from a dropout detection circuit to identify the presence or absence of such recorded information, but accurate identification is difficult because there is an essential difference between dropout and the presence or absence of recorded information.

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus for identifying the presence or absence of recorded information in a recording disc playback device, which can accurately identify the presence or absence of recorded information on a video disc or the like to prevent the motor or pickup from running out of control, and can also be used for end detection. .

For video discs, for example, the video signal is a standard NTSC signal that is directly FM modulated.
For audio signals, a so-called multiplex recording method is used in which a carrier frequency lower than that of the FM carrier of the video signal is FM-modulated, and then the FM carrier of the video signal is superimposed in the form of pulse width modulation. At the inner circumference of the video disc, the high-frequency components of the reproduced RF signal must be attenuated and become smaller than at the outer circumference, but the RF carrier signal component containing the audio information in the reproduced RF signal is at that frequency. Since the signal is relatively low, it has a nearly constant level regardless of the inner or outer circumference of the disk, so if the carrier component FM modulated by this audio signal is detected, the presence or absence of recorded information can be determined on the inner and outer circumference of the disk. This means that accurate discrimination can be made regardless of the relationship.

The device for identifying the presence or absence of recorded information in a disc playback device of the present invention utilizes the fact that the carrier level of an audio device containing audio information is approximately constant, and detects this carrier level to identify the presence or absence of recorded information. This is what I did.

The present invention will be explained below with reference to the drawings.

The figure is a block diagram showing an embodiment of the present invention.
The level of the reproduced RF signal is controlled by an AGC (automatic gain control) circuit 1 to eliminate variations in the reproduced RF level due to differences in reflectivity of the disks and variations in pickup laser output. This automatically gain-controlled reproduced RF signal is applied to an equalizer circuit 2 to compensate for a drop in the level of high-frequency components at the inner circumference of the disk. BPF is used to separate the video information signal and audio information signal from this compensation output.
(bandwidth filter) 3 and LPF (low pass filter) 4
are provided, and each separated output is input to each FM demodulation circuit 5 and 6 and converted into a video output and an audio output.

A level detection circuit 7 is provided to detect the output level of the BPF 3, that is, the level of the video information signal, and the equalizer characteristics of the equalizer 2 are controlled in accordance with this level to compensate for the high frequency components of the video information. On the other hand, a level detection circuit 8 detects the output level of the LPF 4, that is, the level of the audio information signal.
is provided, and AGC circuit 1 is set according to this level.
The gain is controlled and AGC is applied.

In the present invention, the detection output (also the AGC output) of the level detection circuit 8 for detecting the level of the audio information signal is used as one input of the comparator 9, and is compared with the reference voltage that is the other input.
This comparison output is used as a recorded information presence/absence identification signal. If this reference voltage level is set to approximately ground potential, for example, as long as there is recorded information on the disk, the output of the comparator 9 can be maintained at a high level to identify the presence of recorded information, and the presence of recorded information can be identified. If it is not present, the output of the comparator 9 is inverted, making it possible to identify the "absent" state, thereby preventing system runaway and enabling end detection. There are also cases where there is video information but no audio information, but in such a case, only the audio carrier is necessarily present, so it is possible to identify the recorded information from the structure shown in the figure.

According to the present invention, the presence or absence of recorded information is determined by detecting the FM carrier level of audio information, which has no difference in level depending on the inner and outer circumferences of the disk, so there is no risk of malfunction and the structure is simple. It is something that can be done.

It goes without saying that the block in the above embodiment is not limited to this, and can be modified in various ways.

[Brief explanation of the drawing]

The figure is a block diagram of an embodiment of the invention. Explanation of symbols of main parts, 8...Audio information signal level detection circuit, 9...Level comparator.

Claims (1)

[Claims] 1. A recording information presence/absence identification device in a playback device for a disc in which a carrier signal is modulated by an audio signal and recorded together with video information, and a level for detecting the level of the carrier signal extracted from a playback RF signal in the playback device. An apparatus for identifying the presence or absence of recorded information, comprising: a detection means; and a comparison means for generating an identification signal indicating that there is no recorded information when the level detected by the level detection means is less than a predetermined value.