JPS6180530A - Tracking servo circuit - Google Patents

Abstract

PURPOSE:To perform invariably the best tracking servocontrol by controlling the gain of a variable gain circuit according to a tracking error signal when a light beam makes a scan across plural groove or pit arrays, and maintaining the control gain. CONSTITUTION:The difference output of reflected or transmitted light obtained by projecting the light beam upon a recording medium where pregroove or pit arrays are formed is passed through the variable gain circuit to obtain the tracking error signal. The input and output terminals of the variable gain circuit are connected to one input terminal and output terminal of an analog multiplier 20 respectively, and the output of the multiplier 20 is supplied to a holding circuit 24 through an envelope detecting circuit 21, differential amplifier circuit 22, and voltage comparing circuit 23. The gain of the multiplier 20 is controlled with the output of the circuit 24. The switch SW1 of the circuit 24 is turned on during a crossing scan on groove or pit arrays formed on the recording medium, and turned off when tracking servocontrol is on. Thus, the gain of the tracking servo circuit is controlled to perform invariably the best servocontrol.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical recording/reproducing device, and particularly to a tracking servo circuit.

(Prior Art) Conventionally, a light beam is projected onto a recording medium in which grooves are formed or a recording medium in which pit rows are recorded, and the reflected light or transmitted light is received by at least two photoelectric conversion elements.
The differential output of this photoelectric conversion element is detected as a tracking error signal. Tracking servo circuits for optical recording and reproducing devices are known.

However, since tracking servo is performed using the differential output of the divided amounts of received light, there is a drawback that the gain of the tracking servo circuit changes depending on changes in the light reflectance of the recording medium and the amount of light beam. To solve this problem, a method of detecting the total amount of light incident on the photoelectric conversion element and controlling the gain of the tracking servo circuit to a constant value was proposed in Japanese Patent Application No. 51-515.
Proposed by No. 59 (Special Publication No. 57-56138) etc. □
has been done.

(Problem to be Solved by the Invention) Since the total amount of light received by the photoelectric conversion element is hardly affected by the depth of the groove or pit row formed on the recording medium, However, the tracking servo circuit has the disadvantage of being unstable or oscillating.

(Means and actions for solving the problem) A light beam is projected onto a recording medium in which a groove is formed or a pit row is recorded, and the reflected light or transmitted light is received by at least two photoelectric conversion elements. However, in a tracking servo circuit that obtains a tracking error signal for tracking servo by passing the differential output of this photoelectric conversion element through a variable gain circuit, when multiple grooves or pit rows are scanned across with the light beam, Controlling the gain of the variable gain circuit according to the tracking error signal during the cross-scanning so that a tracking error signal of a prescribed output is obtained, and controlling the variable gain circuit thereafter to maintain the control gain. A tracking servo circuit characterized in that it is equipped with gain control means.

(Embodiment) The present invention solves the above-mentioned drawbacks, and one embodiment will be described in detail below with reference to the drawings. Note that parts not directly related to the tracking servo circuit are omitted for the sake of brevity.

FIG. 2 is a block diagram showing an optical recording/reproducing apparatus having a tracking servo circuit according to the present invention.

Reference numeral 1 denotes a recording medium, on which grooves 11 are formed in a predetermined track shape, and a recording layer 12 is further coated. 2
is a motor shaft, 3 is a light source such as a laser diode, 4 is a collimating lens that condenses the light beam of light g3, 5 is a prism that corrects the spread angle of the light beam in the vertical and horizontal directions, 6 is a half mirror, and 57 is a An objective lens 8 that creates a minute spot on the recording medium 1 is an actuator that moves the objective lens 7 in the tracking direction based on a tracking error signal, which will be described later. 91.9□ is a photoelectric conversion element that detects the reflected light beam from the recording medium 1 that is split by the half mirror 6; It is arranged in the boundary region with the photoelectric conversion elements 9□ and 92 to receive the reflected light beam. The dotted line indicates the main optical path of the light beam.

10 is an adder that adds the outputs of the photoelectric conversion elements 91.9□. 11 is an analog divider, and the reference voltage V
ref is divided by the output of adder 10 to produce an output that is inversely proportional to the input signal. 12 is a low-pass filter that removes high-frequency components of the output of the analog divider 11.
13.14 is an amplifier that amplifies the output of the photoelectric conversion element 9□, and the gain of the amplifier 14 is the same as that of the photoelectric conversion element 91.9.
It is variable in order to correct output errors due to misalignment of □, variations in sensitivity, etc. 15 is a differential amplifier that outputs the output difference of amplifiers 13 and 14 as a tracking error signal. An analog multiplier 16 generates an output obtained by multiplying the output of the differential amplifier 15 and the output of the low-pass filter 12.

The light reflectance of the recording medium 1 is determined by the above circuit configuration.

This realizes a tracking servo circuit whose gain does not change due to changes in the amount of light beam. 17 is a variable gain circuit according to the present invention, 18 is a phase compensation circuit, and 19 is an output buffer for the actuator 8.

The variable gain circuit 17 in FIG. 2 will be explained in detail with reference to FIG. In the figure, 20 is an analog multiplier, and broken lines 21 to 24 are an envelope detection circuit, a differential amplifier circuit, a voltage comparison circuit, and a hold circuit, respectively.

The input and output terminals of the variable gain circuit 17 are connected to the analog multiplier 2, respectively.
It is connected to one input terminal of 0 and the 8-power terminal. The output of the analog multiplier 20 is connected to the base of the PNP transistor Tr, the collector of the transistor Tr is connected to the negative power supply -B, and the emitter is connected to the NPN transistor Tr.
, connected to the base of. Also, the transistor Tr□
The emitter of is connected to the collector of the transistor Tr and the positive power supply element B via a resistor R□. A resistor R2 and a capacitor C□ are connected between the emitter of the transistor Tr2 and the ground, and the emitter of the transistor Trz is connected to the inverting input terminal of the operational amplifier 25 via a resistor R1.

Further, the output of the analog multiplier 20 is connected to the base of the NPN transistor Tr3, the collector of the transistor Tr is connected to the positive power supply B, and the emitter is connected to the base of the PNP transistor Tr4. Further, the emitter of the transistor Tr is connected to the transistor T via a resistor R4.
r, and is connected to the negative power supply -B. A resistor R6 and a capacitor C2 are connected between the emitter of the transistor Tr4 and the ground, and the emitter of the transistor Tr is connected to the non-inverting input terminal of the operational amplifier 25 via the resistor R6.

A non-inverting input terminal of the operational amplifier 25 is connected to ground via a resistor R7. A resistor R is connected between this inverting input terminal and the output terminal, and a resistor R9 is connected to the output terminal.
It is connected to the inverting input terminal of the operational amplifier 26 via the inverting input terminal of the operational amplifier 26.

The non-inverting input terminal of the operational amplifier 26 is connected to the reference voltage source Vref.
It is connected to the. Further, a resistor R1° is connected between the inverting input terminal and the output terminal, and the output terminal is further connected to the inverting input terminal of the operational amplifier 27 via the resistors R, □ and the switch So+. The non-inverting input terminal is connected to ground, and a capacitor C3 is connected between the inverting input terminal and the output terminal. Here, the switch Sw1 is turned on by a control circuit (not shown) during a tracking signal detection mode in which a light beam cross-scans a plurality of grooves formed on a recording medium in a focus-on state.
When the tracking servo is in the on state in the recording or reproducing mode, it is controlled to be in the off state. Since the operational amplifier 27 is used as an analog hold circuit, an operational amplifier such as Intersil's ICH8500, which has a very small bias current, is used.

The output terminal of the operational amplifier 27 is connected via a resistor R1□ to the other input terminal of the analog multiplier 20 and the cathode of a diode D□ whose anode is connected to ground. Here, the resistor R2 and the diode D discharge the negative voltage from the hold circuit 24 when the power is turned on, and prevent it from being input to the multiplier 20.

The operation of the above-mentioned circuit will be explained below with reference to FIG. Note that (a) shows the tracking error signal input to the variable gain circuit 17, and (b) to (f) show the multiplier 20, the envelope detector 21, the differential amplifier circuit 22, and so on. Voltage comparison circuit 2
3 and the output voltages of the hold circuit 24 are shown.

When the tracking signal detection mode is selected, a substantially sinusoidal tracking error signal is input to the variable gain circuit 17. In the initial state, since the capacitor C1 of the hold circuit 24 is in an uncharged state, the output voltages of the hold circuit 24, multiplier 20, envelope detector 21, and differential amplifier circuit 22 are respectively at ground level, and the voltage comparison circuit 2
3 is ground level and basis +! ! A differential output of the voltage V ref is output to the hold circuit 24 . Here, the output voltage of the hold circuit 24 is the time integral of the current flowing into the capacitor C1, that is, when the output voltage of the voltage comparison circuit 23 is V x and the output voltage of the hold circuit 24 is vy, the output voltage is determined by the time constant of Rise. When a voltage is input from the hold circuit 24, the analog multiplier 20 outputs a tracking error signal with an amplitude proportional to the output voltage of the hold circuit 24. The upper and lower envelopes of this tracking error signal are detected by the envelope detection circuit 21, and the differential amplifier circuit 22 outputs the potential difference between the upper and lower envelopes output from the envelope detector 21 to the voltage comparison circuit 23.

The voltage comparison circuit 23 outputs a comparison output between the output of the differential amplifier circuit 22 and the reference voltage V ref to the hold circuit 24 .

As a result of the output voltage of the hold circuit 24 gradually increasing, the output voltage of the differential amplifier circuit 22 increases. Therefore, the output voltage of the voltage comparison circuit 23 gradually decreases, and the hold circuit 2
When the current flowing into the hold circuit 24 begins to decrease and the output voltage of the voltage comparator circuit 23 reaches the ground level, the hold circuit 24
There is no current flowing into the hold circuit 24, and the hold circuit 24 outputs a constant voltage. In this way, since the analog multiplier is controlled to always keep the potential difference between the upper and lower envelopes output from the envelope detector 21 constant, a constant specified output can always be obtained from the variable gain circuit. Tracking servo that is not affected by variations in groove depth depending on the recording medium can be realized.

When the tracking servo gain control for the recording medium 1 is completed in the tracking signal detection mode, the switch Sw1 is turned off, no current flows into the hold circuit 24, and a hold state is entered in which a constant voltage is output to the analog multiplier 20. The gain set during tracking signal detection mode can be maintained.

In addition, when the hold circuit 24 is configured with an analog circuit,
The hold value changes somewhat with the passage of time, but as a countermeasure for this, it is possible to update the hold value by using the above-mentioned tracking signal detection mode in the fast-forward mode or the like.

Further, the present invention is not limited to the above embodiments; for example, the hold circuit 24 is configured with an analog circuit, but it may be configured with a digital circuit by A/D converting the output of the differential amplifier 23. You can also do it. In addition, various embodiments are possible, such as being able to be configured with a four-division photoelectric conversion element instead of a two-division photoelectric conversion element.

(Effects of the Invention) According to the present invention, the gain of the tracking servo circuit can be controlled for the groove or pit row formed on the recording medium, so it is possible to always configure the best tracking servo circuit. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the invention, FIG. 2 is a circuit diagram of a variable gain circuit of the invention, and FIG. 3 is a diagram for explaining the invention. DESCRIPTION OF SYMBOLS 1... Recording medium, 11... Groove, 3... Light source, 4... Collimating lens, 5... Prism, 6...
...Half mirror 17...Objective lens, 8...Actuator, 91,9□...Photoelectric conversion element, 13.1
4...Amplifier, 15...Differential amplifier, 17...
Variable gain circuit.

Claims (1)

[Scope of Claims] Projecting a light beam onto a recording medium in which a pregroove is formed or a recording medium in which a pit row is recorded, and receiving the reflected light or transmitted light by at least two photoelectric conversion elements,
In a tracking servo circuit that obtains a tracking error signal for tracking servo by passing the differential output of this photoelectric conversion element through a variable gain circuit, when a plurality of grooves or pit rows are scanned across with the light beam, a specified tracking output is obtained. controlling the gain of the variable gain circuit according to the tracking error signal during the cross-scanning so that an error signal is obtained;
A tracking servo circuit comprising gain control means for controlling the variable gain circuit so as to maintain the control gain thereafter.