JPS6076032A - Focus control circuit of disk record reproducer - Google Patents

Abstract

PURPOSE:To perform the gain control of focus search independently of that of focus servo by providing a switch circuit which leads the output signal of a focus search gain control circuit to the reference potential point and to the reverse input terminal of an amplifying circuit. CONSTITUTION:In a focus search operating mode, a feedback circuit which consists of a level control circuit 23 and a feedback resistance R11 is connected to an amplifying circuit, a phase compensating circuit 20 and a drive circuit 21 respectively. The focus search gain is controlled by controlling the variable resistance VR2 of the circuit 23 regardless of the variable resistance VR1 of the circuit 18. In a focus servo operating mode, a capacitor C3 charged in the focus search operating mode is discharged. At the same time, the output of the circuit 23 is led to the earth. The focus servo gain is controlled by controlling the resistance VR1 of the circuit regardless of the resistance VR2 of the circuit 23.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a disc record playback device suitable for, for example, an optical CD (conductor disc) type DAD (digital audio disc), and particularly focuses on This invention relates to a device that can perform r-in adjustment of a search signal.

[Technical background of the invention]

Recently, in the field of audio equipment, digital recording and playback methods that utilize PCM (alpha code modulation) technology are being adopted in order to achieve high-fidelity playback as much as possible. In other words, this is what is called digital audio conversion, and the principle is to make the audio characteristics independent of the characteristics of the recording medium and to be far superior to conventional analog recording and playback methods. This is because it has been established.

In this case, a system that uses a disk as a recording medium is called a DAD system, and optical, electrostatic, and mechanical recording and reproducing methods have been proposed. Regardless of which method is adopted, the playback device that embodies it must be able to satisfy a variety of advanced control functions and performance that are not found in American devices. .

In other words, if we take the CD system as an example,
A transparent resin disk with a diameter of 12 cm3 and a thickness of 1.2 m: is coated with a metal thin film that forms bits (irregularities with different reflectances) corresponding to digital (PCM) data.・The CLV (Constant Linear Velocity) method is used to drive the rotation at variable rotational speeds of about 500 to 200 [r, p, m,], which is then driven by an optical pickup with a built-in half-quad laser and a photoelectric conversion element. It plays in a linear tracking manner from the inner circumferential side to the outer circumferential side.
The track pitch of this disc is 16 [μm], and the program area (radius 25 to 58 [mn:
]), and their index data etc. are recorded in the lead-in area (radius 23 to 25 [: m
This can be easily seen from the fact that it is recorded in

By the way, in the above-mentioned CD type DAD playback device, what is particularly important is that the light beam emitted from the semiconductor laser of the optical pickup is used to accurately read the digitized data recorded on the disk without errors. For the objective lens that condenses the light beam, a focus length is set so that the focus (spot) of the light beam is always on the signal recording surface of the disk, and the focus length of the light beam is set so that the spot is located from the pit row to the disk. Tracking servo is applied to accurately trace the pit row without shifting in the radial direction.

In this case, the objective lens is held in a predetermined position by a biasing force such as a spring when the DAD playback device is in a non-operating state, and is brought into contact with the biasing force of the spring when the power is turned on. A so-called focus search is performed in which the lens is moved to the focal position @, and after reaching the focal position through this focus search, the focus servo is switched to the focal position and controlled to be held at the focal position.

Here, FIG. 1 shows the conventional focus length search, focus search, and tracking serve means. That is, the reference numeral 11 in the figure is a photodetector (photoelectric conversion element) built into the optical pickup. This photodetector 1 is of a four-division type, for example, four light-receiving areas P D a using photodiodes.
-P D d is formed, and a light beam (reflected light) that is changed depending on the presence or absence of a bit on the disk is irradiated onto the center thereof. The four light-receiving areas PDa-PDd of this photodetector 1
By receiving the above-mentioned reflected light, each of them independently outputs a frequency No. 16 Pa=Pd corresponding to the presence/absence of the above-mentioned bit. However, each output level of this frequency signal Pa-Pd is different from the light receiving area PDa.
= It changes according to each amount of light received by PDd.

The frequency signals Pa to Pd thus obtained are selectively supplied to the oscillators 12 to 124 constituting the matrix circuit 12, respectively.

Tsumashi, this matrix circuit No. 2 is Pa+Pb.

It generates four frequency signals: Pc +Pd, Pa +Pc, and Pb +Pd, among which PR+
Pb.

The two signals Pe+Pd are supplied to input terminals 131 and 132 of the pickup control integrated circuit No. 3, respectively, and the two signals Pa+Pc, , Pb+Pd are supplied to the input terminals 131 and 132 of the pickup control integrated circuit No. 3 through coupling capacitors C1 and C2, respectively. Input terminal 1 of integrated circuit J3 for pickup control
33,134.

Here, the pickup control integrated circuit 13 is a central integrated circuit for performing the focus search, focus search, and tracking serve, and includes a focus error signal generation circuit J4, a switching control circuit 15, and a low frequency oscillator 16. , focus detection circuit 17, amplifier circuit 18
and a tracking error signal generation circuit 19. Although the original operation is to start with a focus search, here, in order to make the explanation easier to understand, we will first discuss the focus search.

That is, the focus error signal generation circuit 14
It is composed of a subtraction circuit consisting of an operational amplifier OP7 and resistors R1 to R4, and assuming that the disc is currently being played stably, the Pa supplied through the input terminals 131 and 132 is
It outputs a voltage signal corresponding to the phase difference between two frequency signals, +Pb and Pc -1-Pd. This voltage signal becomes the focus error signal FE corresponding to the focal deviation of the light beam on the signal recording surface of the disk, and the signal becomes O[v] level when the objective lens is at the in-focus position. However, this objective lens still has a voltage characteristic such that, for example, when the objective lens approaches the disk with respect to the focal point position, the polarity becomes positive, and when it moves away from the focal point, the voltage becomes negative.

Here, the focus error signal FE is supplied to the first fixed terminal a of the switching control circuit 15. The second fixed terminal of this switching control circuit 15 is supplied with the output of a low frequency oscillator J6 for focus search, which will be described later.

The switching control circuit 15 switches the movable terminal C to the second fixed terminal side when an H (high) level signal is output from the focus detection circuit J2.

Although the details will be described later, the seven-occurrence detection circuit 17 is connected to the input terminal J33. No.3
By determining whether the levels of the two frequency signals Pa + Pc * Pb + Pd supplied to 4 are above or below a predetermined value, it is detected whether the objective lens is near the in-focus position. When the objective lens is near the in-focus position, the H level signal (7-occasion OK signal)
When the objective lens is not near the in-focus position, an L level signal is output.

Therefore, as mentioned above, when the disc is being played back stably, the objective lens is located near the focused position, so the focus detection circuit 17 outputs an H level signal. The movable terminal C of the switching control circuit 15
is connected to the first fixed terminal a. Therefore, the focus error signal FE output from the seven-occurrence error signal generation circuit J4 is supplied to the amplifier circuit No. 8 via the switching control circuit 15. This amplifier circuit J8 includes an operational amplifier OP2, resistors R5゜R6, and a big alar f control φ.
Output terminal 35 and input terminal 36 of integrated circuit 3 for 1j
It is something like a variable resistor VRI connected externally between the
By adjusting this variable resistor VRI, the level of the focus error signal FE can be changed, and the focus error signal FE can be changed. The gain can be adjusted.

The focus error signal whose level has been adjusted by the amplifier circuit J8 is then sent to the phase compensation circuit 20 and the operational amplifier OP.
3. It is supplied to a focus actuator coil 22 for driving the objective lens in the focus direction (perpendicular to the disk surface) through a drive circuit 2 including resistors R7 and R8. For this reason, the objective lens is always controlled to be at the focused position, and the focus search is performed at this position.

Next, the focus search will be explained. first,
When the DAD playback device is in a non-operating state, the objective lens is held at a given position (for example, the farthest position from the disk) by a biasing force such as a spring, as described above. When the power is turned on to the DAD playback device in this state, a light beam is irradiated from the semiconductor laser, but since the objective lens is not at the focused position, the amount of light reaching the photodetector I is small, and each received light beam is The frequency signal Pa=Pd output from the area is at a low level. This results in l), Pa-1-Pc and P
Since the levels of the two frequency signals b + Pd also become low, the focus detection circuit J7 eventually outputs an L level signal and connects the movable terminal C of the switching control circuit 15 to the second fixed terminal b (11). This causes the low frequency oscillator 1
6 is now supplied to the amplifier circuit 18.

This low frequency oscillator 16 outputs a triangular wave voltage signal (focus search signal) OSC having a frequency of, for example, 1 to 4 (R2), and this focus search signal O8C causes the objective lens to move to the aforementioned predetermined position. The lens is moved from this position in the direction of the in-focus point (the direction closer to the disk), and a focus search is performed here. Then, as the objective lens approaches the in-focus point, the level of each frequency signal Pa-Pd increases sequentially, and when the objective lens reaches the vicinity of the in-focus point position, the focus detection circuit 17 outputs an H-level focus OK signal and switches. Movable terminal C of control circuit 15
is connected to the first fixed terminal &111tl, and the focus search is completed here. and,
Instead, the focus error signal FE is used to control the focus position to be maintained at all times.

Then, when the objective lens is deviated from the focused position due to an external impact etc. while the focus servo is being applied as described above, each frequency signal Pa -
Since the level of Pd becomes low, the output of the focus detection circuit NOR becomes L level, and as a result, the objective lens is moved to the vicinity of the in-focus position as described above by the focus search signal O8C from the low frequency oscillator 16, and then again. This allows the focus direction to be adjusted.

Note that the input terminal 1 of the pickup control integrated circuit 13
The two frequency signals Pa+PcPb+Pd supplied to 33 and 134 are supplied to the tracking error signal generation circuit J9.

This tracking error signal generation circuit J9 has the above-mentioned Pa
-1-Pc, Pb +Pd A voltage corresponding to the phase difference between the two frequency signals (Q is output. And this voltage signal is a tracking corresponding to the deviation from the pit row of S/,) This is the error signal TE, which is at 0 [V] level when the spot is on the pit row.For example, when the spot deviates from the pit row toward the outer circumference of the disk, it becomes positive polarity, and when it deviates toward the inner circumference, it becomes negative polarity. It was made to become so. This tracking error signal TE is led out to the outside via the output terminal 137 of the pickup control integrated circuit 13, and is used to drive the objective lens in the tracking direction (radial direction of the disk) via a drive circuit (not shown). is supplied to an actuator coil (not shown). For this reason,
The objective lens is controlled so that the spot is always located on the pit row, and the tracking sensor is located here. is to be carried out.

[Problems with background technology]

By the way, in the conventional DAD playback device, as mentioned above, the force sensor? dyne; in is possible, but gain adjustment for focus search is not possible. As explained in FIG. 1, the focus error signal FE and focus search signal O8C
are amplified by the gains set by the amplifier circuit 8, the phase compensation circuit 20, and the drive circuit 2. In this case, the variable resistor VRI of the amplifier circuit J8 gives priority to the shifted focus error signal FE. Therefore, the gain of the focus search signal O8C is inevitably determined by the adjusted value. Therefore, if the above adjustment value is small with respect to the best gain of the focus search signal OSC, the time required for focus search will be unnecessarily long, and if the above adjustment value is large, the objective lens will move during focus search operation. When the speed is too fast and the focus OK signal is output and the focus search is completed, the focus? - If the objective lens is focused at the focal point position, the color will be lost. Therefore, it has been strongly desired to be able to adjust the gain of the multi-focus search independently of the dyne adjustment of the focus servo.

[Purpose of the invention]

This invention was made in order to improve the above-mentioned problems, and provides an extremely good focus control circuit for a disc record playback device that can perform focus search gain adjustment independently of focus servo gain adjustment. The purpose is to provide.

[Invention (ll’l: male:]

That is, the focus control circuit of the disc record playback device according to the present invention includes a switching control circuit that selectively derives a focus error signal and a focus search signal depending on whether or not a focus OK signal is generated, and an inverting input terminal and a non-inverting input terminal. an amplifier circuit having an input terminal, supplying a signal derived by the switching control circuit to the non-inverting input terminal, and connecting a focus servody adjustment circuit between the inverting input terminal and the output terminal; a drive circuit for amplifying an output signal and outputting it to the seven orcus actuator coils for controlling the movement of the objective lens; and adjusting the level of the output signal of this drive circuit and outputting it to the inverting input terminal of the amplifier circuit. A focus search dyne adjustment circuit capable of adjusting a focus search dyne, and the focus OK
The present invention is characterized by comprising a switch circuit that guides the output signal of the focus search dyne adjustment circuit to a reference potential point and an inverting input terminal of the amplifier circuit depending on whether a signal is generated.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG. However, in FIG. 2, the same parts as in FIG. 1 are designated by the same reference numerals, and only the different parts will be described here.

FIG. 2 shows its configuration, and the output of the drive circuit 2 is supplied to the focus actuator coil 22 and also to the level adjustment circuit 23. This level adjustment circuit 23 includes a resistor R9,
R) 0, variable resistor VR2 and phase compensation capacitor c3
The output of the drive circuit 2 is connected to resistors R9 and R
1O and variable resistance VR? The level is set at , and outputted from the input terminal 38 of the pickup control integrated circuit J3.

Inside the pickup control integrated circuit i3, the output of the switch circuit for discharging the capacitor C3 and the level adjustment circuit 23 is connected to the amplifier circuit 18 via the feedback resistor R11 via the input terminal 13B. Inverting input terminal (-) of operational amplifier OP2
A switch circuit 24 consisting of a switch s2 for supplying
is configured. Each of the switches 81 and 82 of this switch circuit 24 is controlled on/off in response to the output of the seven focus detection circuit NOA, and an L level ITO signal is output from the focus detection circuit 17. When the switch circuit is turned off and the switch s2 is turned on, the H level focus is OK from the 7-occurrence detection circuit 12.
When a signal is output, switch SL is on, switch S
2 is turned off.

The operation of the above configuration will be described below.

First, to explain the focus search, for example, when the power is turned on to the current DAD playback device, the objective lens is not near the in-focus position, so as mentioned above, an L level signal is sent from the focus detection circuit NOA. Output. Therefore, in the switching control circuit 15, the movable terminal C
is connected to the fixed terminal, and the switch circuit 2
The switch circuit No. 4 is set to the OFF state, and the switch S2 is set to the ON state. During the focus search operation, a feedback circuit including a level adjustment circuit 23 and a feedback resistor R11 is connected to the amplifier circuit 1B, the phase compensation circuit 20, and the drive circuit 2.

In this case, the focus search signal O8C, which is the output of the low frequency oscillator J6, is supplied to the amplifier circuit J8 via the switching control circuit 15, but until this focus search signal O8C is output to the focus actuator coil 22. The transfer characteristic of can be expressed as follows. That is, assuming that the input level of the amplifier circuit 18 is vin, the output level is vl, the output level of the drive circuit 2 is 2, and the output level of the level adjustment circuit 23 is v3, the transfer characteristic of the amplifier circuit 18 is expressed as follows. Ru. Further, the transfer characteristic of the drive circuit 2 can be expressed as follows. Furthermore, the transfer characteristic of the level adjustment circuit 23 can be expressed as follows. Here, by substituting equations (1) and (3) into equation (2), we get: Therefore, when we solve equation (4) for ■2, we get:

Furthermore, by substituting N into equation (5) and rearranging it, we get the following. Here, R4, (R, +R,.+VR2)<R4゜(R5+VR
1) Assuming A-(7), the above equation (6) becomes as follows: As long as the value of the variable resistor VR is sufficiently thick compared to the resistors R5 and R6, the focus search signal O8C is ultimately transmitted. The characteristic can be expressed as .

That is, the focus search signal O8C is given a transfer characteristic expressed by the qQ equation and is output to the focus actuator coil 22. The gain adjustment can be performed by adjusting the variable resistor vR2 of the level adjusting circuit 23, regardless of the variable resistor VR1 of the amplifier circuit 18, as is clear from equation 101.

Next, the focus tape will be explained. When the objective lens moves close to the in-focus position based on the focus A signal O8CK, the focus detection circuit 17 outputs an H level focus OK signal. Therefore, in the switching control circuit 15, the movable terminal C is connected to the fixed terminal a side, and the switch 87 of the switch circuit 24 is set to the on state and the switch S2 is set to the off state. In other words, during focus serve operation,
The switch of the switch circuit 24 discharges the capacitor C3 charged during the focus search operation, and the switch S2 leads the output of the level adjustment circuit 23 to the ground, so that the feedback circuit during the focus search operation ends up being used. has been separated.

In this case, the seven focus error signal FE is supplied to the amplifier circuit 18 via the switching control circuit 5, but the transfer characteristic until this focus error signal FE is output to the focus actuator coil 22 is as follows. It is expressed as follows. That is, the transfer characteristics of the amplifier circuit 18 are:
v −R5+R6+VR1vIn 15111. (1
1) −R6, and the transfer characteristics of the drive circuit 2 are v=R, +
R8■ ,,,,,,,.

2 R8', the transfer characteristic given to the focus error signal FE is R,+R8R5+R6+VR.

v--vin・・・・・・ari -R8R6 It is expressed as

That is, the focus error signal FE is given a transfer characteristic expressed by the zero-order equation and is output to the focus actuator coil 22. And the gain adjustment is (
As is clear from Equation 131, the variable resistance VR of the amplifier circuit 18,
This can be done by adjusting the

Therefore, if the focus control circuit of the DAD playback device is configured as described above, each gain adjustment of the focus search and focus chi can be performed independently, and thereby the output gain of the focus couch signal O6C can be adjusted independently. You will be able to adjust it easily.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide an extremely good focus control circuit for a disc record reproducing apparatus that can perform focus search gain adjustment independently of focus servo gain adjustment.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram for explaining the focus search and tracking servo means of a conventional disc record playback device, and FIG. 2 is a focus diagram of a disc record playback device according to an embodiment of the present invention. FIG. 2 is a block circuit diagram showing a control circuit. 1 No... Photodetector, 12... Integrated circuit for matrix up control, 14... Focus error signal generation circuit, 15... Switching control circuit, J6... Low frequency oscillator, J7... Focus detection Circuit, 18... Amplification circuit, No. 9... Tracking signal/1d signal generation circuit, 20... Phase compensation circuit, 2 No. 1/2... Mem motion circuit, 2
2... Focus actuator coil, 23...
Level MiIfi adjustment circuit, 24... switch circuit, F
E...Focus error signal, osc...7 focus search partner number, VR1+VB2'' variable resistor, OP
, ~OP3... operational amplifier.

Claims (1)

[Scope of Claims] The information signal is read out from a disc on which the information signal is recorded by using an optical pickup, and the objective lens of the optical pickup is used for focus search (based on No. 8, from an initial setting position to a focused point). a focus search means for moving the objective lens to a position close to the focus position; a focus detection means for detecting by the focus search means that the objective lens has reached the vicinity of the in-focus position and generating a focus OK signal; and generation of the focus 0K4fl. a focus servo means for controlling the objective lens to be pulled into the in-focus position according to a focus error No. 4g generated based on the output signal of the optical pickup in the state; a switching control circuit that selectively derives the focus error signal and the focus search signal depending on whether or not the focus OK signal is generated; and the switching control circuit has an inverting input terminal and a non-inverting input terminal. an amplifier circuit configured by supplying the derived signal to the non-inverting input terminal and connecting a focus length-bore-in W multiplier circuit between the inverting input terminal and the output terminal; and amplifying the output signal of the amplifier circuit. A drive circuit outputs the output signal to a focus actuator coil for controlling the movement of the objective lens, and an output signal of this drive circuit is outputted to the inverting input terminal of the amplifier circuit at a level alf to generate a sharp force snarch r-in. an adjustable focus search gain adjustment circuit and an output signal of the focus search gain adjustment circuit depending on whether or not the focus OK signal is generated; A focus control circuit for a disc record playback device patented as comprising a switch circuit.