JPS6211427B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a recording disk reproducing device that uses a recording disk on which high-frequency information signals such as audio signals and video signals are recorded, and the object thereof is to record high-frequency information signals such as audio signals and video signals at the outer peripheral position of the recording disk. It is an object of the present invention to provide a recording disk reproducing device that can effectively correct the difference in amplitude between the reproduction output from a detection element and the reproduction output from a detection element at an inner circumferential position.

Generally, as this type of recording disk reproducing apparatus, a recording disk reproducing apparatus that utilizes a recording disk (hereinafter referred to as a video disk) on which video signals are recorded at high density is known. As one of the recording and reproducing methods for this video disk, a recording disk without grooves is used to record video signals in the form of pits on a spiral track using a light beam. A method has been proposed in which the position of a detection element is controlled while referring to a tracking control signal recorded simultaneously in a guard band between tracks, and the signal is reproduced.

In the recording/reproducing method using the recording disk described above, the main track on which information signals as video signals are recorded and the sub-tracks on which control signals for tracking are recorded are detected by the same detection element (e.g. photoelectric pickup, capacitance). The signal from the main track is restored to a video signal through an FM demodulator, for example, and the control signal from the sub-track is used to make the detection element follow the main track correctly while referring to its amplitude. Supplied to the servo circuit. Also, when a video disk is rotated at a constant speed (for example, 900 revolutions per minute), the recording wavelength on the disk for a signal of a certain frequency is proportional to the radius at which the recorded track is located, and if the track is on the inner circumference, As time progresses, the recording wavelength becomes shorter. On the other hand, since the detection element is always picked up with a constant size (for example, the spot diameter of the light beam in a photoelectric pickup or the electrode thickness in a capacitance pickup), the detection element moves toward the inner circumference. Accordingly, the output amplitude of the detection element decreases. This phenomenon is more pronounced as the recording frequency increases, so the degree of amplitude reduction when proceeding to the inner track is different between the playback device for the high frequency main track and the playback signal for the low frequency sub track. The rate of decline is greater for the reproduced signal from.

Therefore, by adding an automatic gain control (AGC) circuit to deal with the above phenomenon, it is possible to equalize the output amplitude from the detection element, but if the amplitude of the signal from the main track is kept constant, Since the signal from the sub-track becomes too large, the tracking servo system becomes unstable, and conversely, if the amplitude of the signal from the sub-track is kept constant, the signal from the main track becomes small at the inner circumference. Therefore, the S/N ratio of the video signal deteriorates.

The present invention solves the above-mentioned contradiction, and effectively adds automatic gain control (AGC) circuits to at least one of the signals from the main track and the signals from the sub-track. Mainly,
The amplitude of the signals from each sub-track is corrected.

The present invention will be described below with reference to drawings of embodiments.

FIG. 1 is an enlarged view of the recording tracks of the video disc to which the present invention is applied, in which FM-modulated video signals are recorded in the frequency band of 6 to 8 MHz on the main track 1, and on the sub-tracks 2, 2′ has tracking control signals of 500KHz and 700KHz, respectively.
recorded at the frequency of The tracking control signal is recorded during the horizontal synchronization signal period to avoid beat interference with the video signal.

FIG. 2 shows the output signal waveform from the detection element when the track of the video disc shown in FIG. This is the output signal waveform at the periphery. The tracking control signal from the secondary truck is the same as the tracking control signal from the main truck.
It appears on the envelope of the FM video signal. Since the frequency of the FM video signal from the main track is about 10 times higher than that of the tracking signal from the sub-track, the rate of amplitude decrease is large as it advances toward the inner circumference.

FIG. 3 is a schematic configuration diagram showing an example of the reproducing apparatus of the present invention, in which 3 is a video disk, 4 is a capacitive pickup, and signals recorded in the form of pits on the surface of the video disk 3 are shown. is detected in the form of a change in capacitance between the needle tip electrode and the disk, and converted into an electrical signal. The electrical signal from the pickup 4 is amplified by a preamplifier 5 and then separated into a main signal and a tracking signal by a high-pass filter 6 and a low-pass filter 7. The main signal passed through the filter 6 is corrected for the amplitude drop at the inner circumference by, for example, an average value AGC circuit 8 having a relatively long time constant, and the tracking signal passed through the filter 7 is corrected for the amplitude drop at the inner circumference. corrects the amplitude drop at the inner circumference by, for example, a peak value AGC circuit 9 having a relatively short time constant. The main signal whose amplitude has been made uniform by the AGC circuit 8 is restored to a video signal by the FM demodulator 10, and the tracking signal is controlled by the servo circuit 11 to position the pickup 4 at the center of the main track. It turns out.

As mentioned above, when separate AGC is added to the main signal and the tracking signal, the deterioration of the S/N of the video signal is reduced because the decrease in the amplitude of the main signal is corrected while going from the outer circumference to the inner circumference. Furthermore, since the amplitude reduction of the tracking signal is corrected, the gains of the servo system on the outer and inner circumferences are equalized, resulting in the effect that stable servo can always be applied.

In the above embodiment, a video signal was recorded as an information signal on the main track, but it goes without saying that this information signal may be an audio signal.

As described above, the present invention utilizes a recording disk having a main track on which a high-frequency information signal is recorded and a sub-track adjacent to the main track on which a tracking control signal having a frequency different from that of the information signal is recorded. In the playback device, automatic gain adjustment circuits are provided for the signal transmission paths of the playback signal of the main track and the playback signal of the subtrack, so that the information signal recorded on the main track and the playback signal of the subtrack are It is possible to provide a recording disk reproducing device that can maintain each recorded tracking signal at a constant level, always performs tracking correctly, and does not deteriorate the S/M ratio.

[Brief explanation of the drawing]

FIG. 1 is an enlarged view of a track of a video disc to which the present invention is applied, and FIG. 2 is a signal waveform when the disc of FIG. FIG. 3 is a diagram of output signal waveforms at the inner peripheral portion of the disk, and is a schematic configuration diagram showing an example of the reproducing apparatus of the present invention. 3... Disk, 4... Pickup, 5... Preamplifier, 6, 7... Filter, 8, 9... AGC circuit,
10...FM demodulator, 11...servo circuit.

Claims (1)

[Claims] 1. Reproduction using a recording disk having a main track on which a high-frequency information signal is recorded, and a sub-track adjacent to the main track on which a tracking control signal having a frequency different from that of the information signal is recorded. A recording disc reproducing apparatus characterized in that an automatic gain adjustment circuit is provided for each of the signal transmission paths for the reproduction signal of the main track and the reproduction signal of the sub-track. 2. Claims characterized in that the automatic gain adjustment circuit is provided for at least one signal transmission path after the main track reproduction signal and the sub-track reproduction signal are separated by a frequency band division filter. 2. The recording disk reproducing device according to item 1.