JPH02214026A - Optical disk device - Google Patents

Abstract

PURPOSE:To obtain an optical disk device in which no offset occurs in each error signal even for the data recording part of an optical disk by providing a timing generating means to generate the timing of a prescribed operation corresponding to the presence/absence of data recording. CONSTITUTION:Since the timing to select the output signals Va and Vb of photoelectric conversion elements A and B and the sampling timing of sample and hold circuits 9 and 10 can be obtained by a selector 6 synchronizing with a reproducing signal in the timing generating means (7, 24-27) when an optical beam 5 arrives at the data recording part of the optical disk 1, the signals Va and Vb are added at an adder 24, and a signal proportional to a reflected light quantity is generated, and the signal via a capacitor 25 is waveform- arranged at a comparator and logic circuit 26, and a select signal SEL, sampling signals SA and SB, and a signal SLCT representing a recording section are outputted by using the above result. In such a way, a selector 27 selects a signal 2 from the timing circuit 7 when the optical beam arrives at an unrecording part, and a signal 1 from the circuit 26 when it arrives at the recording part, and outputs them to the selector 6 and the circuits 9 and 10, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical disc device that optically records and/or reproduces information on a recording medium.

[Conventional technology]

In an optical disk device, a light beam modulated by information is focused on an optical disk to record information, or a light beam is focused on an optical disk and the reflected light is used to reproduce information. This optical disc device is provided with a tracking control device and a focus control device in order to always focus the light beam on a target position on the optical disc.

This tracking control device and focus control device obtain a tracking error signal and a focus error signal that are proportional to the amount of deviation of the light beam from the target position (tracking error and focus error of the light beam), and perform tracking control and focus error signals based on these signals. Focus control is being performed.

FIG. 4 shows an example of an optical disc device.

This example is characterized in that one voltage-controlled amplifier is used in a time-division manner in a general optical disc device. A recording medium 1 consisting of an optical disk is rotationally driven by a motor, and an objective lens 2. A light beam 5 is irradiated by an optical device including an optical system 3 and a split-type photodetector 4, and information is optically recorded or reproduced. Information is recorded on concentric or spiral tracks on the optical disc 1, and the optical device moves in the radial direction of the optical disc 1 to record or reproduce information on the tracks on the optical disc 1.

The split type photodetector 4 includes a photoelectric conversion element A divided into two parts,
It has B. The optical system 3 includes a light source, which condenses and irradiates a light beam 5 onto the optical disk 1 through the objective lens 2, and uses the reflected light as a well-known optical system for tracking error detection (or focus error detection). The light is made incident on the split-type photodetector 4 through a photodetector (optical system) for photoelectric conversion. The signals Va and Vb detected by the photoelectric conversion elements A and B become equal to 1 if there is no ranking error (or focus error), and the selector 6 outputs the output signal V of the photoelectric conversion elements A and B.
a, Vb as the select signal SEL from the timing circuit 7
is selected and inputted to the voltage control amplifier (VCA) 8. As shown in FIG. 5, this select signal SEL becomes high level and low level alternately at a constant frequency, and the selector 6 selects the output signal Va of the photoelectric conversion element A when the select signal SEL is at a high level. When the select signal SEL is at a low level, the output signal vb of the photoelectric conversion element B is selected.

The output signal of the voltage control amplifier 8 is converted into sample signals SA, S generated from a constant frequency clock from the timing circuit 7 in a sample/hold circuit (S/H) 9.10.
B is sampled and held in synchronization with the select signal SEL. As shown in Fig. 5, the sample signal SA
is generated when the select signal SEL is at a high level, and the sample/hold circuit 9 receives the output signal Va of the photoelectric conversion element A.
The output signal of the voltage control amplifier 8 corresponding to the sample signal SA is sampled. Further, the sample signal SA is generated when the select signal SEL is at a low level, and the sample-and-hold circuit 10 outputs the output signal vb of the photoelectric conversion element B.
The output signal of the voltage control amplifier 8 corresponding to the sample signal SB is sampled. With such a configuration,
By using one voltage-controlled amplifier 8 in a time-division manner, the same effect as using two voltage-controlled amplifiers with equivalent characteristics can be obtained. In principle, it is sufficient to set the sampling period T of the sample-and-hold circuit 9.10 to a time corresponding to twice the frequency of the band required for tracking control (or focus control). This frequency is at most several 10K
Since it is H2, sampling by the sample-and-hold circuits 9 and 10 is easy.

Output signal S Ha of sample and hold circuits 9 and 10.

SHb is subtracted by the differential amplifier 11 to become a tracking error signal (or focus error signal) SHa-8Hb. Based on this error signal 5Ha-8Hb, the servo circuit 12 drives the actuator 13 to move the objective lens 2, thereby performing tracking. Tracking control (or focus error control) is performed to eliminate the error (or focus error).

In addition, the output signal SHa of the sample and hold circuits 9 and 10
, SHb are added by a summing amplifier 14, and after high frequency noise is removed by a low pass filter (LPF) 15, a differential amplifier 16 calculates the target voltage V ra of the power supply 17.
Subtracted from f. The subtraction result Vc of this differential amplifier 16
The gain of the voltage controlled amplifier 8 is controlled so that the output of the summing amplifier 14 is always equal to the target voltage V ref.

Now, if the output signals V a and V b of the photoelectric conversion elements A and B are a and b when the reflectance of the optical disk 1 is 1, then when the reflectance of the optical disk 1 is R, the output signals of the photoelectric conversion elements A and B are The output signals Va and Vb are Ra.

It becomes Rb. Also, the gain G of the voltage control amplifier 8 is 0R (
a+b)-Vref, so G
= Vref/R(a + b). The output 5Ha-8Hb of the differential amplifier 11 is as follows, and since Vref/(a + b) is a constant, the output of the differential amplifier 11, that is, the tracking error signal (or focus error signal) SHa-8Hb is the output of the optical disc 1. It is independent of reflectance and always provides a constant loop gain.

FIG. 6 shows an example of the configuration of the voltage control amplifier 8. As shown in FIG.

This example is an operational amplifier A and a junction field effect transistor Q.
and resistors R1, R, and the operational amplifier A amplifies the output signal of the selector 6.

The field effect transistor Q receives the output signal V of the differential amplifier 16.
The drain-source resistance changes due to c, which changes the gain of the operational amplifier.

FIG. 7 shows an example of the configuration of the timing circuit 7. As shown in FIG.

FIG. 8 is a timing chart showing the operation. This example has a counter 18, a D flip-flop 19°20,
Gate 21. , 22, and the counter 18 counts the clock CLK from the clock generator. D
The flip-flop 19 latches the second digit output of the counter 18 using the clock CLK from the clock generator, and
Flip-flop 20 latches the output of D flip-flop 19 using clock CLK from a clock generator. Gate 21 generates a sample signal SA by ANDing the non-inverted output of D flip-flop 19, the inverted output of D flip-flop 20, and the first digit output of counter 18; is inverted and ANDed with the non-inverted output of the D flip-flop 19 and the inverted output of the D flip-flop 20 to generate the sample signal SB. This sample signal SA.

SB has a length of 16 clocks CLK.

Further, the first digit output of the counter 18 is output as a select signal SEL.

[Problem to be solved by the invention]

In the above optical disc device, the error signals 5Ha-5Hb are controlled to be O during dragging (or focusing), so the photoelectric conversion element A.

The signals Va and Vb detected at B are equal.

Here, when the light beam 5 reaches a portion of the optical disc 1 where data is recorded, the reflectance of the optical disc 1 is changed by the recording pit 23 on the optical disc 1, so that a photoelectric conversion element A is generated as shown in FIG.

The signals Va and Vb detected at B change simultaneously due to changes in the reflectance of the optical disc 1. However, although the selector 6 selects the output signals Va and Vb of the photoelectric conversion elements A and B in a time-divisional manner to alternately generate the sample signals SA and SB of the sample-and-hold circuits 9 and 10, this sample signal Since SA and SB are generated from a clock of a constant frequency by the timing circuit 7 and are not necessarily synchronized with the data reproduction frequency, the sample and hold circuits 9 and 10
For the data recording section of the optical disc 1, the signals Va and Vb at specific levels are sampled every time.
Low frequency undulations are generated in the output signals S Ha and S Hb. As a result, an offset Voff may occur in the error signal 5Ha-8Hb, resulting in track deviation (or focus deviation). Figure 9 shows sample signals SA, S
This is a timing chart of this device when the frequency of B is an integer fraction of the data recording frequency, and in this case, the offset V off is DC. Further, if the frequency of the sample signals SA, SB is not an integer fraction of the data recording frequency, the offset V off becomes a low frequency undulation, which cannot be ignored for the track servo system (or focus servo system).

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and to provide an optical disc device that does not cause an offset in a tracking error signal (or focus error signal) even in a data recording section of an optical disc.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a split photodetector including at least a first photoelectric conversion element and a second photoelectric conversion element that receives reflected light obtained by irradiating a recording medium with a light beam; A selection means for time-divisionally selecting the output signals of the first photoelectric conversion element and the second photoelectric conversion element, a voltage control amplifier to which the signal from the selection means is input, and an output signal of the voltage control amplifier. at least two sample-and-hold circuits that sample each output signal of the first photoelectric conversion element and the second photoelectric conversion element during each period in which the selection means selects each output signal of the first photoelectric conversion element and the second photoelectric conversion element;
a gain control loop that adds the output signals of the two sample and hold circuits and controls the gain of the voltage control amplifier so that the addition result is equal to the reference voltage; and a control device for calculating a tracking error signal or a focus error signal and controlling a tracking state or a focus state of the light beam on the recording medium based on the signal, in which the selection means selects the first the timing for time-sharingly selecting the output signals of the photoelectric conversion element and the second photoelectric conversion element;
The sampling timing of one sample-and-hold circuit is generated based on the result of waveform shaping of a signal corresponding to the reflectance change for a location where data on the recording medium is recorded as a change in reflectance, and For locations where data is not recorded, timing generation means is provided for generating timing using a clock of a constant frequency.

[For production]

Reflected light obtained by irradiating the recording medium with a light beam is received by a split photodetector including at least a first photoelectric conversion element and a second photoelectric conversion element.

The output signals of the first photoelectric conversion element and the second photoelectric conversion element are time-divisionally selected by the selection means.

The signal from this selection means is amplified by a voltage control amplifier, and the output signal of this voltage control amplifier is used for each of the output signals of the first photoelectric conversion element and the second photoelectric conversion element selected by the selection means. Each period is sampled by at least two sample-and-hold circuits. The output signals of the at least two sample-and-hold circuits are added by a gain control loop, and the gain of the voltage-controlled amplifier is controlled so that the addition result is equal to a reference voltage, and the control device controls the output signals of the at least two sample-and-hold circuits. A tracking error signal or a focus error signal is obtained by calculating the difference between the output signals of , and the tracking state or focus state of the light beam on the recording medium is controlled based on this signal. The timing at which the selection means selects the output signals of the first photoelectric conversion element and the second photoelectric conversion element in a time-sharing manner and the sampling timing of the two sample-and-hold circuits are determined by the timing generation means. For locations where data on the recording medium is recorded as a change in reflectance, a signal is generated by waveform shaping the signal corresponding to the change in reflectance, and for locations where data on the recording medium is not recorded. Generated by a constant frequency clock.

〔Example〕

FIG. 1 shows an embodiment of the invention.

In this embodiment, the adder 24.
AC coupling circuit 25 consisting of a capacitor. Comparator/logic circuit 26. A selector 27 is added, and the same parts as the optical disc device described above are given the same reference numerals.

In this embodiment, when the light beam 5 approaches the data recording section of the optical disc 1, the selector 6 selects the photoelectric conversion element A,
The timing for time-divisionally selecting the output signals Va and Vb of B, and the sample/hold circuit 9. In order to obtain the IO sampling timing in synchronization with the reproduced data, the output signals Va and Vb of the photoelectric conversion elements A and B are added by an adder 24 to generate a signal proportional to the amount of light reflected from the optical disc 1. Then, the comparator/logic circuit 26 shapes the waveform of the signal input from the adder 24 via the capacitor 25, and uses the results to output a select signal SEL and sample signals SA, SB, and also indicates a data recording section. Outputs signal 5LCT. This signal 5LCT
Accordingly, when the light beam 5 approaches a part of the optical disc 1 that is not a data recording area, the selector 27 receives the select signal SEL and the sample signal SA from the timing circuit 7.
SB is selected and output to the selector 6 and the sample/hold circuit 9.10, and when the light beam 5 approaches the data recording section of the optical disc 1, the comparator/logic circuit 26
Select signal SEL and sample signals SA, SB from
selector 6 and sample/hold circuit 9,
Output to 10.

FIG. 2 shows the configuration of the comparator/logic circuit 26,
FIG. 3 is a timing chart thereof.

Signal a inputted from adder 24 via capacitor 25 is compared with Ov by zero cross comparator 28, waveform-shaped, inverted by inverter 29, and output as select signal SEL. Although not shown, this signal S
The output signal of the EL or zero cross comparator 28 is sent to a higher-level controller as a normal reproduction information signal.

Further, the input signal a is compared with the constant voltages +E and -E of the power supply 35.36 by comparators 30 and 31, and its waveform is shaped.

At the rising edge of the output signals c and d of the comparators 30 and 31, the flip-flops 32 and 33 are set, respectively.

And this flip-flop 32 is the zero cross comparator 2
The flip-flop 33 is reset at the falling edge of the output signal SEL of the inverter 29. This flip-flop32.
The output signals e and f of 33 are sample signals SA whose sampling timings are alternately the zero-crossing points of the input signal a,
Output as SB.

These select signals SEL and sample signals SA, S
When the light beam 5 approaches the data recording section of the optical disc 1 due to the photoelectric conversion element A.

B's output signals Va and Vb always show the same level (
The waveform shaping point) is sampled by the sample-and-hold circuits 9 and 10, and the signals Va and Vb of the sample-and-hold circuits 9 and 10 no longer have undulations, resulting in an error signal 5H.
Offset Voff no longer occurs at a-8Hb.

On the other hand, when the light beam 5 approaches a portion of the optical disc 1 that is not a data recording area, the output signal of the comparator/logic circuit 26 becomes unstable.

In this case, even if the timing at which the selector 6 time-divisionally selects the output signals Va and Vb of the photoelectric conversion elements A and B and the sampling timing of the sample-and-hold circuits 9 and 10 are fixed timings as in the conventional case, Therefore, the select signal SEL and the sample signals SA and SB from the timing circuit 7 are selected by the selector 27 and output to the selector 6 and the sample/hold circuits 9 and 10.

Furthermore, in order to obtain a signal 5LCT indicating whether or not the portion of the optical disc 1 that is irradiated with the light beam 5 is a data recording section, the output signal d of the comparator 31 is input to the retriggerable mono-multivibrator 34. , the output signal g of this mono multivibrator 34 is a signal 5LCT. Here, the mono multivibrator 34 operates at the falling edge of the input signal. The selector 27 selects the output signal of the comparator/logic circuit 26 when the signal 5LCT is at a high level, and selects the output signal of the timing circuit 7 when the signal 5LCT is at a low level.

In this embodiment, in an automatic gain control circuit including a selector 6, a voltage control amplifier 8, and sample/hold circuits 9 and 10, a signal corresponding to the amount of reflected light from the optical disk 1 is shaped into a waveform, and the voltage is controlled only at the rising or falling edge of the signal. amplifier 8
Sample and hold the output signal of 9. Since sampling is performed at 1O, there is no low frequency waviness or offset in the sampling result for the data recording section of the optical disc 1, and therefore the error signal 5Ha-S
No offset occurs in Hb either. In addition, a sample and hold circuit 9,
Since the sampling timing of 10 is switched to a fixed timing, normal gain control operation can be performed even in areas where no data is recorded.

〔Effect of the invention〕

As described above, according to the present invention, there is provided a split photodetector including at least a first photoelectric conversion element and a second photoelectric conversion element that receive reflected light obtained by irradiating a recording medium with a light beam; a selection means for time-divisionally selecting the output signals of the first photoelectric conversion element and the second photoelectric conversion element; a voltage control amplifier to which the signal from the selection means is input; and a voltage control amplifier for selecting the output signal of the voltage control amplifier. at least two sample-and-hold circuits that sample each output signal of the first photoelectric conversion element and the second photoelectric conversion element in each period in which the selection means selects each output signal, and the at least two sample-and-hold circuits; and a gain control loop that controls the gain of the voltage control amplifier so that the addition result is equal to the reference voltage, and a tracking error that calculates the difference between the output signals of the two sample and hold circuits. In the optical disc apparatus, the selection means includes a control device that obtains a signal or a focus error signal and controls a tracking state or a focus state of the light beam on the recording medium based on the signal. The timing for time-divisionally selecting the output signal of the second photoelectric conversion element and the sampling timing of the two sample-and-hold circuits are set relative to the location where data on the recording medium is recorded as changes in reflectance. The system is equipped with timing generation means that generates a signal corresponding to the reflectance change by waveform shaping, and generates a signal using a constant frequency clock for areas where data is not recorded on the recording medium. Tracking or focusing can be performed accurately with respect to the data recording section without causing an offset in the tracking error signal or the focus error signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram showing a comparator/logic circuit of the same embodiment, FIG. 3 is a timing chart of the same embodiment, and FIG. 4 is a conventional one. A block diagram showing the optical disk device, FIG. 5 is a timing chart of the device, FIG. 6 is a circuit diagram showing the voltage control amplifier of the device, FIG. 7 is a block diagram showing the timing circuit of the device, and FIG. 8 is a block diagram showing the timing circuit of the device. FIG. 9 is a timing chart showing the operation of the timing circuit, and FIG. 9 is a timing chart of the above device. 1... Recording medium, 4... Divided photodetector, 6...
Selection means, 8... Voltage control amplifier, 9, 10... Sample and hold circuit, 11.12... Control device,
14.16...gain control loop, 7.24-27...
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Claims (1)

[Claims] a split photodetector including at least a first photoelectric conversion element and a second photoelectric conversion element that receive reflected light obtained by irradiating a recording medium with a light beam; the first photoelectric conversion element and the second photoelectric conversion element; a selection means for time-divisionally selecting the output signal of the photoelectric conversion element; a voltage control amplifier into which the signal from the selection means is input; and the selection means selects the output signal of the voltage control amplifier from the first photoelectric conversion element. At least two sample-and-hold circuits that sample each output signal of the conversion element and the second photoelectric conversion element in each selected period, and the output signals of the at least two sample-and-hold circuits are added together. A gain control loop that controls the gain of the voltage control amplifier so that the result is equal to a reference voltage, and a difference between the output signals of the two sample and hold circuits are calculated to obtain a tracking error signal or a focus error signal. In the optical disc apparatus, the selection means controls the output signals of the first photoelectric conversion element and the second photoelectric conversion element. and the sampling timing of the two sample-and-hold circuits are determined by a signal corresponding to the reflectance change where the data on the recording medium is recorded as a change in reflectance. 1. An optical disc apparatus comprising: a timing generating means that generates timing based on the result of waveform shaping, and generates timing using a constant frequency clock for areas where data is not recorded on the recording medium.