JPS5920167B2 - information reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an information reproducing apparatus using a disc on which information is frequency-multiplexed recorded.

Conventionally, as seen in radio receivers or television receivers, in order to select and demodulate multi-frequency radio waves, a method is known in which frequency conversion is performed using a local oscillator and a mixer and demodulation is performed. A mixer is essential in this method. Currently, in an information reproducing device that reproduces information by rotating a disc on which information is frequency multiplexed at a constant speed, it is conceivable to convert the frequency of the photoelectrically converted reproduced signal using a local oscillator and a mixer, but this method Then a mixer is essential. Also, a high-speed photoelectric converter is required to read the highest recorded frequency. In view of the above points, the present invention modulates the light source for signal regeneration at a substantially constant frequency, thereby omitting the mixer that is indispensable in the conventional system, simplifying the configuration of the regeneration circuit, and simplifying the configuration of the photoelectric converter. Provided is an information reproducing device that can employ an inexpensive photoelectric converter by lowering the required frequency 5 characteristics, and can perform stable signal reproduction by controlling the modulation frequency according to the amplitude of the reproduced signal. It is something to do.

FIG. 1 is a block diagram of an optical information reproducing apparatus showing an embodiment of the present invention. In the figure, 1 is a light source that is optically modulated, 2
is a beam splitter, 3 is a condensing lens, 4 is a disk on which information is recorded with an uneven surface, 5 is a motor that rotates the disk 4 at a constant speed, 6 is a photoelectric converter, and T is a filter. , 58 is a demodulation circuit, 9 is an output terminal, 10
1 is a light source modulation circuit, 11 is a local oscillator, 12 is a bias voltage generation circuit, and 13 is an amplitude detection circuit. FIG. 2a shows the spectrum of the signal recorded on the disk 4, and FIG. 2b shows the passband characteristics of the filter T.

In FIG. 1, the optical path of light emitted from a light source 1 is bent at right angles by a beam splitter 2, and then condensed by a lens 3 to be focused on the surface of a disk 4.

On the disk 4, two signals shown in FIG. 2a are frequency-multiplexed and recorded. 1 out of 2 signals
One is modulated with carrier frequency j, and one with carrier frequency j2, whose bandwidths are the same but do not overlap with each other.

This frequency-multiplexed signal is recorded in a spiral shape on the surface of the disk 4 as a physical deformation of unevenness. The light focused on the disk surface undergoes changes in reflectance and diffraction due to the unevenness, and then passes through the lens 3 and the beam splitter 2.
and is converted into an electrical signal by a photoelectric converter 6. The filter 7 has the passband characteristics shown in FIG. 2b, and its center frequency F3 and bandwidth are equal to that of the signal recorded on the disk 4.

Now, assuming that the local oscillator 11 is oscillating at a frequency FLa, the light source modulation circuit 10 is excited at this frequency, and the light source 1 is driven by the light source modulation circuit 10.

The light intensity of the light source 1 changes at a frequency FLa. When such light is focused on the surface of the disk 4 and a signal is read out, the light incident on the photodetector 6 is FLa<! :Fl, f2
It contains information on the sum and difference frequencies of , which is .

These two pieces of information are processed by the filter 7 into the carrier wave f1 shown in equation 3.
Only the signal that has been low frequency converted from the carrier wave F to the carrier wave F is selected, and the demodulation circuit 8 demodulates the signal recorded on the carrier wave f1. The oscillation frequency of the local oscillator 11 is changed by the voltage generated by the bias voltage generation circuit 12.

Now, if this is changed and the oscillation frequency is set to FLb, the light incident on the photodetector 6 contains information on the sum and difference frequencies of FLb<5-Fl, f2, which is.

Of these two pieces of information, only the low frequency converted signal from the carrier wave F2 shown in equation (8) is selected by the filter 7,
In the demodulation circuit 8, the signal recorded on the carrier wave F2 is demodulated. In this way, bias voltage generation circuit 1
By changing the bias voltage that is the output of 2, one of the two pieces of information is demodulated. In reality, the irregular rotation of the motor 5 and the disc 4
Due to the eccentricity of the disk 4, the signal read from the disk 4 is
Subject to time axis fluctuations.

Therefore, the signal selected by the filter 7 is sent to the amplitude detection circuit 1.
3, and by detecting this and slightly changing the oscillation frequency of the local oscillation circuit 11, the time axis fluctuation is canceled out where the light from the light source 1 and the reflected light from the disk 4 are mixed, A stable signal with no time axis fluctuation is demodulated and outputted to an output terminal 9 after the demodulation circuit (8). In the above embodiment, two types of signals are recorded on the disk 4, but the present invention can also be applied to a case where more than two types of signals are multiplexed.

As described above, according to the information reproducing device according to the present invention, the configuration of the reproducing circuit can be simplified by omitting the mixer, and the necessary frequency characteristics of the photoelectric converter can be lowered, so that an inexpensive photoelectric converter can be used. There is.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical information reproducing apparatus showing an embodiment of the present invention, and FIG. 2a is a diagram showing a spectrum b of a signal recorded on a disk showing the passband characteristics of a filter. In the figure, 1 is a light source, 2 is a beam splitter, 4 is a disk, 5 is a motor, 6 is a photoelectric converter, 7 is a filter, 8 is a demodulation circuit, 11 is a local oscillator, 12 is a bias voltage generation circuit, and 13 is a This is an amplitude detection circuit.

Claims (1)

[Claims] 1. In an information reproducing device that optically reproduces desired information from a disk-shaped recording medium in which multiple pieces of information are frequency-multiplexed and recorded as signal stripes consisting of physical deformations on the surface, a readout light source is modulated at a nearly constant frequency. a switching means for switching the modulation frequency of the modulation means in accordance with a carrier wave frequency of an information signal to be reproduced; and means for condensing the light modulated by the modulation means onto the disk-shaped recording medium. a photoelectric converter that converts reflected light or transmitted light from the disc-shaped recording medium into an electrical signal; a filter to which the output of the converter is input;
a demodulation circuit for demodulating the signal that has passed through this filter; an amplitude detection circuit for amplitude detection of the output of the filter; and means for controlling the output frequency of the modulation means in accordance with the output of the amplitude detection circuit. An information reproducing device characterized by comprising: