JPS6123570B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical information reproducing device, and more particularly to a video disk information reproducing device using laser light.

There is an optical recording method as a method for recording predetermined information on an information recording medium such as a video disk. Such optical recording methods use standard NTSC video signals.
By FM modulating it and converting it into an FM signal, on the other hand, also FM modulating the audio signal, mixing both FM signals with an appropriate amplitude ratio, and then passing it through a limiter.
The video FM signal is further pulse-modulated with the audio FM signal, multiplexed, and recorded on a video disc.

An optical modulator is used when recording on this video disk, and a rectangular wave of the video FM signal frequency whose duty ratio changes according to the audio FM signal is applied to this optical modulator, and the laser light that passes through this modulator is applied to the optical modulator. This is what is called intensity modulation by turning on and off. This modulated laser light forms a video track by sequentially arranging pits called pits in a spiral pattern on the video disk, thereby recording information.

Such recorded information is read by irradiating the recording surface with a laser beam and causing a photoelectric conversion element to receive reflected light or transmitted light from the recording surface.

In this case, the frequency characteristics of the read RF signal vary depending on the information recording position on the video disc, and generally the frequency characteristics deteriorate as the video track gets closer to the inner circumference, and the level of the video FM carrier signal component decreases. There is. In order to compensate for the frequency characteristics depending on the video disk position,
The color burst level of the demodulated signal of the read RF signal (FM modulated signal) is detected and the frequency characteristic compensation circuit is controlled according to the amount of change to correct the frequency characteristic.

However, with such a compensation method, depending on the state of the recorded video disc, the amount of change in the demodulated burst level may not always correspond to the change in frequency characteristics, so it is difficult to accurately The disadvantage is that compensation is difficult.

An object of the present invention is to provide an optical information reproducing device that can correctly compensate for changes in the frequency characteristics of an RF signal due to changes in the information recording position on a video disc.

The optical information reproducing device of the present invention takes advantage of the fact that the DC component of the output converted into an electric signal by the photoelectric conversion means is independent of the position of the disk, and extracts the DC component of the electric signal. means for generating a first voltage according to the level; and means for detecting the FM carrier level of the electric signal and generating a second voltage according to the level;
comprising means for comparing the first and second voltages and generating a control signal according to the difference; and equalizer means for amplifying and compensating the electric signal and configured to change frequency characteristics according to the control signal. It is characterized by

Hereinafter, the present invention will be explained using the drawings.

The figure is a block diagram showing an embodiment of the present invention.
A photoelectric converter 1 composed of a photodiode or the like converts the disk reflected light or transmitted light into an electrical signal. This signal is an FM modulated RF signal, and after being amplified in the next stage RF amplifier 2,
It is applied to the equalizer circuit 3. This equalizer circuit has a frequency characteristic compensation circuit configuration whose frequency characteristics are variably controlled by a control signal Vf. The output of this circuit 3 is demodulated by an FM demodulator 4 and
The signal is input to a carrier level detector 5 which detects the level of the RF carrier signal and generates a voltage Vc according to the detected level.

On the other hand, a DC amplifier 6 is provided which detects only the DC component of the reproduced signal of the photoelectric converter 1 and generates a voltage V _D according to its level, which is compared with the previous voltage Vc in a comparator 7, and both voltages Vc A control signal Vf is generated according to the difference between and _VD . This control signal
For example, the frequency characteristics of the equalizer 3 can be changed by changing the capacitance value of a variable capacitance diode or the like that determines the frequency characteristics using Vf.

Therefore, according to the present invention, it is possible to keep the frequency characteristics of the reproduced RF signal almost constant, regardless of changes in the amount of light due to disc reflectance or differences in light sources, or regardless of the recording state of the disc. . Therefore, the carrier of the audio FM signal and the video FM
Since the ratio of the carrier levels of the signals is always substantially constant, the beat of the audio signal to the video signal can be significantly improved, especially at the inner circumference of the video disk.

[Brief explanation of the drawing]

The figure is a circuit block diagram showing an embodiment of the present invention. Explanation of signs of main components, 1...Photoelectric conversion element,
3... Equalizer, 5... Carrier level detector, 6... DC amplifier, 7... Comparator.

Claims (1)

[Claims] 1. An optical information reproducing device that reads and reproduces information by irradiating light onto the recording surface of an information recording medium on which predetermined information is FM-modulated and recorded, and converts the light that has passed through the recording surface into an electrical signal. a conversion means for
means for extracting a DC component of the electric signal and generating a first voltage according to its level; means for detecting the FM carrier level of the electric signal and generating a second voltage according to the level; and a comparison means for comparing the first and second voltages and generating a control signal according to the difference; and an equalizer means for amplifying and compensating the electric signal and configured to have a frequency characteristic changed by the control signal. Characteristic optical information reproducing device.