JPH10105987A - Focus control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce probability of failure in focus search. SOLUTION: With focusing off, the output from an optical pickup 100 is out of information, so that a sum signal circuit 20 produces no output. Accordingly, ASP(analog signal processor) 200 reports to a control micro computer 400 by a signal DRF that the focusing is off. The micro computer 400 controls a driving source through a timing circuit 42, and performs a focus search. In this case, the control micro computer 400, through a timing circuit 34, causes a reduced speed signal CLV(constant linear velocity) to be outputted from a control circuit 32 for a fixed period. As a result, a driver 500 reduces the number of revolution of a CD. Thus, the focus search is adequately performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus control circuit for controlling a focus in a reading device for optically reading information recorded on an optical information recording medium such as a CD (compact disk).

[0002]

2. Description of the Related Art Conventionally, reading of data written on a CD or the like has been performed by focusing a laser beam on a CD and detecting reflected light. For this focusing, it is necessary to adjust the distance of the optical system that focuses the laser light on the CD with respect to the CD surface. So, CD
At the start of reading data written to the
A focus search for checking the in-focus state is performed by changing the distance from D.

Therefore, when reading is started, first, the rotation of the CD is started, and at the same time, the optical system is sequentially brought close to the CD, and the spot shape of the reflected light is examined. This spot shape is designed to be circular when in focus and too close or too far to have different ellipses oriented at 90 ° to each other.
Therefore, the spot shape of the reflected light is examined, and it is detected that the spot shape has become circular, and the distance of the optical system from the CD is determined.

Further, in the focused state, the intensity of the reflected light from the CD becomes the highest, so that the focused state can be confirmed by the light intensity. Therefore, the in-focus state is confirmed from the state of such reflected light, and focus control is performed.

[0005] Further, the reading of data written on a CD is performed by rotating the CD, so that the number of rotations must be controlled. Therefore, a synchronization signal for controlling the number of revolutions is written on the CD, the synchronization signal is detected from the read data, and the synchronization data is synchronized with an internal clock signal generated in, for example, a CD reproducing device. Thus, the rotation speed of the CD is changed to control the rotation of the CD.

When the focus is deviated due to a physical shock applied to the apparatus, the optical system is moved stepwise as described above, and the in-focus state is restored. In this way, the initial focus search and the focus search at the time of out-of-focus are achieved by the same circuit and the same procedure.

[0007]

Here, in the conventional circuit, the rotation of the CD is accelerated when the focus is lost. In other words, because the RF signal can no longer be obtained,
Upon recognizing out-of-focus, a focus search operation is started, and the pickup is once separated from the CD surface, and then gradually approached to see the in-focus state. At this time, since the operation of this focus search is started in the same procedure as the initial focus search, the CD is accelerated.

[0008] When such acceleration is performed, there is a problem that the probability of occurrence of an error in a focus search operation for observing the state of the RF signal is gradually increased by approaching the pickup gradually.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a focus control circuit for controlling a focus in a reading apparatus for optically reading information recorded on an optical information recording medium, wherein the focus control circuit rotates the optical information recording medium. Then, in the case where information is being read, when the focus of the reader is lost, after reducing the number of rotations, a focus search for adjusting the focus is performed.

As described above, according to the present invention, when the focus is lost, the optical information recording medium (eg, CD)
The focus search is performed by reducing the rotation speed of. Therefore, surface runout and the like are reduced, and the possibility that the focus search fails is reduced.

Therefore, according to the same procedure as in the initial focus search, an effective focus search can be performed without accelerating the CD.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

First, the apparatus basically includes an optical pickup 100, an ASP (analog signal processor) 2
00, DSP (Digital Signal Processor) 300,
It comprises a control microcomputer 400. The optical pickup 100 receives the reflected light from the CD, and outputs a signal corresponding to the received light. The ASP 200 is an optical pickup 10
In response to the signal from 0, it outputs a control signal for the position of the optical pickup and a signal for CD rotation. Also, DSP3
00 is the optical pickup 1 obtained via the ASP 200
Data is demodulated from the signal from 00, and a signal for CD rotation control based on the state of the data is A
Supply to SP200. The control microcomputer 400 is an ASP
200, and controls the overall operation of the device such as the operation timing of the DSP 300.

The optical pickup 100 is provided with photodiodes 12 and 14, each of which detects light (for example, reflected light) read from a CD.

Here, although two photodiodes are shown in the drawing, they are actually composed of four light receiving elements A, B, C and D, and output two sums in diagonal directions. This is the photodiodes 12 and 14. That is, there are four light receiving elements A, B, C, D,
The photodiode 12 outputs a signal of (A + C), and the photodiode 14 outputs a signal of (B + D).

Further, the intensity of the reading light in the optical pickup 100 is configured such that (A + C) and (B + D) become the same during focusing and a difference is produced between these when out of focus. Therefore, the in-focus state can be detected by detecting (A + C)-(B + D). Further, it is possible to determine whether the distance is too close or too far from the sign of the difference.

The ASP 200 has amplifiers 16 and 18, and outputs of the photodiodes 12 and 14 are supplied to the amplifiers 16 and 18, respectively. This amplifier 16, 18
Amplifies the read signals from the photodiodes 12 and 14, respectively, and amplifies the read signals from the sum signal circuit 20 and the difference signal circuit 2.
Feed to 2. The sum signal circuit 20 includes the photodiode 1
This circuit generates the sum of the outputs 2 and 14, and the output (A + C) + (B + D) is a read output. on the other hand,
The output (A + C)-(B + D) of the difference signal circuit 22 is a signal indicating the focus state.

The output of the sum signal circuit 20 is VCA (Vol
stage Control amplifier) 24
Supplied to The VCA 24 is an automatic level control circuit that amplifies the read signal supplied from the sum signal circuit 20 to a predetermined level. Accordingly, the amplitude level of the read signal whose input level changes is controlled here to be substantially constant and output.

The output signal of the VCA 24 is supplied to a comparison circuit 26. The comparison circuit 26 has Vref-0.4
A constant voltage of V is supplied. Then, the comparison circuit 26 compares the two, and the output signal of the VCA 24 is Vre
When f-0.4V or more, "H" is output.
That is, when an AC signal of a sufficient level has been obtained at the output of the sum signal circuit 20, the comparison circuit 26 outputs “H”. The output of the comparison circuit 26 is
00, and the control microcomputer 400
The output "H" indicates that the camera is in focus.

The output of the VCA 24 passes through an amplifier 28,
The signal is supplied to the detection circuit 30 of the DSP 300 as an RF signal. The detection circuit 30 also detects, among the information written on the CD based on the RF signal, a synchronization signal for controlling the rotation of the CD.

That is, the reproduction of the clock and the C
A synchronization signal is written for D rotation control, and the detection circuit 30 detects this synchronization signal.

Then, a signal about the detection result of the synchronization signal and the change state of the RF signal is supplied to the control circuit 32. The control circuit 32 outputs signals CLV + and CLV- on whether to accelerate or decelerate the CD rotation spindle motor in accordance with the detection result of the detection circuit 30. Further, the signal from the timing circuit 34 is also supplied to the control circuit 32, and the acceleration signal CLV is also supplied to the control circuit 32 by the signal from the timing circuit 34.
+, Outputs the deceleration signal CLV-. Timing circuit 34
Is operated by a signal from the control microcomputer 400. Acceleration at the time of starting, an operation at the time of defocusing, and the like are controlled by a signal supplied from the control microcomputer 400 to the control circuit 32 via the timing circuit 34.

The acceleration signal CLV + and the deceleration signal CLV- from the control circuit 32 are supplied to an amplifier 36 of the ASP 200. The amplifier 36 includes an acceleration signal CLV +, a deceleration signal CL
V- is amplified in a predetermined manner and supplied to a rotation control driver 500 of a spindle motor for rotation. Thus, the rotation speed of the CD is controlled.

On the other hand, the output of the difference signal circuit 22 is supplied to a comparison circuit 38. The comparison circuit 38 compares the difference signal with a predetermined constant voltage Vref + 0.2V. The comparison result signal from the comparison circuit 38 is output to the control circuit 40.
Supplied to The control circuit 40 includes a timing circuit 42
, A signal from the control microcomputer 400 is also supplied, and a signal for driving the position of the optical pickup 100 is generated based on these signals.

It should be noted that Vref +
0.2V is a voltage for confirming that the distance has sufficiently approached. After the difference signal has exceeded this value, the control for focusing is performed by controlling the difference signal to approach zero.

That is, when the start of the focus search is supported by the signal from the timing circuit 42, a signal for moving the optical pickup 100 based on the start is generated. Then, a movement signal for focusing is generated.

The output of the control circuit 40 is supplied to a holding circuit 44, D
Optical pickup 1 via an A / A converter 46 and an amplifier 48
00 is supplied to a driving source (not shown) for driving the 00. As a result, an analog voltage corresponding to the output of the control circuit 40 is output from the D / A converter 46, and this output is
And is applied to the drive source. Therefore, the movement of the optical pickup 100 is controlled according to the output of the control circuit 40. Note that the resistor 600 is a feedback resistor of the amplifier 48.

Next, the rotational driving operation of the CD will be described with reference to FIG.
A description will be given based on FIG. First, when a focus search command is output from the control microcomputer 400, the drive source operates via the timing circuit 42 and the control circuit 40, and the optical pickup 100 is once separated from the CD, and then gradually moved to the CD.
Approach D. When the focus state is reached, the sum signal circuit 2
A high frequency signal is obtained at an output of 0. This sum signal circuit 2
When a high-frequency signal is obtained at 0, a constant-level RF signal is supplied to the detection circuit 30 via the VCA 24.

When the synchronization signal is sufficiently detected, the control circuit 32 sets the phase control mode. Then, depending on the state of the detected synchronization signal, CLV +, CV
LV—Alternately outputs and controls the rotation of the spindle motor via the driver 500 by PWM (pulse width modulation) control.

Here, the data included in the RF signal is divided into frames, and one frame is divided into one frame.
Two synchronization signals are inserted. Then, eight or more synchronization signals are detected in 32 frames, and the phase control mode is entered when four or more synchronization signals are detected four or more times in succession.

In this state, if the focus is lost for some reason, the output level of the sum signal circuit 20 is reduced or lost. Then, the detection circuit 30 cannot detect the synchronization signal. Then, it is determined that synchronization detection is less than 8 times in 32 frames.
If it is detected twice consecutively, it enters the rough control mode.
The rough control mode is a mode in which the phase control mode finely adjusts the rotation speed of the CD, whereas the rotation speed is roughly adjusted.

In this embodiment, the "L" of the DRF
Thus, when the control microcomputer 400 detects the defocus, the control circuit 3
2 outputs CLV-. Thus, the rotation of the CD is reduced. Then, the control microcomputer 400 drives the drive source via the timing circuit 42 to perform a focus search. Therefore, the focus search is performed while the rotation of the CD is slow. Therefore, at this time, there is little surface runout and the like, focusing becomes easy, and the probability of occurrence of an error in the focus search is reduced.

However, in the present embodiment, the control circuit 32
Outputs CLV- during this period in response to a command from the control microcomputer 400. Therefore, the rotation of the CD is slow during the focus search. Therefore, the probability that the focus search fails will be sufficiently reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration.

FIG. 2 is a waveform diagram showing an operation state.

[Explanation of symbols]

12, 14 photodiode, 20 sum signal circuit, 2
4 VCA, 26 comparison circuit, 30 detection circuit, 32
Control circuit, 34 timing circuit, 100 optical pickup, 200 ASP, 300 DSP, 400 control microcomputer, 500 driver.

Claims (1)

[Claims] 1. A focus control circuit for controlling a focus in a reader for optically reading information recorded on an optical information recording medium, wherein the information is read by rotating the optical information recording medium. A focus control circuit for performing a focus search for adjusting the focus after the number of rotations is reduced when the focus in the reading device is lost.