JPS58189843A - Optical digital disc player - Google Patents

Abstract

PURPOSE:To prevent the operation of a focus controlling system from being unstable even with the beam amount changed, by irradiating the beam of a prescribed wavelength by a laser light emitting device and irradiating the reflected light on a detector provided with plural photodetecting parts. CONSTITUTION:Even if the amount of light applied to a photodetector 17 without focus error is changed, the output of an adder 41 (i.e., focus error detecting signal) is unchanged. A difference signal of outputs of the adder 41 and a subtractor 22 outputted from a subtractor 43 corresponds to the change in the light amount change of the beam light applied to the photodetector 17 and is negatively fed back to a control input terminal of a laser driving circuit 44. As a result, the circuit 44 drives a laser light emitting device 15 so that the amount of beam light applied to the photodetector 17 is almost constant, thereby minimizing the output of the offset voltage to the output terminal of the subtrators 23 and 24.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an optical digital disc player,
In particular, it relates to improvements in the focus control system.

[Technical background of the invention]

Recently, for the purpose of recording information signals such as audio signals and image signals with high density and reproducing them with high fidelity, it is possible to directly record digitally encoded signals obtained by converting the information signals into 2pCM (Hals code modulation). An optical digital disc player device has been developed which records data on a disc and extracts and demodulates a digital encoded signal from the disc using an optical pickup during playback. This kind of device is
On the other hand, the digitally encoded signal formed by PCM on the ○ surface is directly recorded as pit rows with different pitches on the uneven surface. We are trying to irradiate it with a beam of light. Then, this light beam hits the pit row, is reflected, and is received by the optical pickup.

For this reason, an optical pickup detects the intensity and temporal variation of light and outputs an electrical signal in response to the detection, from which the digitally encoded signal recorded on the disc is extracted.

By the way, what is particularly important in the above-mentioned optical digital disc player is that the beam light [reliably follows the pit row (tracking control)] and that the beam light reliably converges on the pit row. For example, the objective lens position [control a′fru (that is, focus control age)
That's true.

FIG. 1 shows the focus control means and tracking control means of such an optical digital disc player.

That is, in Fig. 1, 1 is a disk, and at the bottom of the figure is an optical pickup [objective lens 1].
2 will be installed. This objective lens 12
is equipped with a moving coil that cooperates with a magnet (not shown) and a magnet (not shown), and is driven by the focus actuator 13 so as to move it closer to or away from the disk 1. Further, the objective lens 11, like the focus actuator 13,
A radial actuator 14 including a magnet and a moving coil (not shown) is capable of moving the disk 11 in the radial direction.

Then, the objective lens 12 is irradiated with a companion beam light emitted from the laser emitter 15 via the beam splitter 16. Therefore, the beam light is transmitted to the objective lens 1.
2 converges onto the disk 11 as shown by the broken line in the figure, changes depending on the presence or absence of bits on the disk 1, and is reflected, travels backwards through the objective lens 12f, and is reflected at right angles to the beam splitter 16 for detection. Here, the photodetector 11 has four light-receiving areas P each composed of a photosensitive element such as a photodiode.
It is a so-called 4-division type with pa to PDdi. When the bump photodetector 17 receives the reflected light from the beam splitter 16, it independently outputs signals Pa to Pdk corresponding to the respective light intensities. However, the can light receiving area PDa
PDd to PDd are configured such that when light of the same intensity is received, the respective output signals Pa to Pd have approximately the same level. Note that the light receiving area PD, to PI)d is P
I), and PDb and PD c and PDd coincide with the tangential direction of the disk 11, and PD, and PDd and P
Db and PDc are arranged to coincide with each other in the radial direction of the disk 1.

Then, the can output signal Pa of the photodetector 1'7
Pd to Pd are supplied to corresponding input terminals of the focus error detection circuit 18 and the tracking error detection circuit 19, respectively.

The focus error detection circuit 1B is, for example, an adder formed of an operational amplifier, ? 0. ．． ? J-work subtractor 22.23
'/f, (Pa + Pb) - (Pc + Pd
) The focus error detection signal [is designed to be output]. In addition, the tracking error detection circuit 1
Reference numeral 9 includes an adder 24.25 and a subtracter 25.26' (for example, operational amplifiers), and outputs a tracking error detection signal r of (P1+Pc)-(Pb+Pd). The error detection signal (Pa+Pc)-(pb+pa) and the tracking error detection signal (Pa+Pc)-(Pb+Pd) are each set to zero when no focus error or tracking error occurs. In FIG. 1, ``■'' and ``V'' are voltage sources for offset compensation of the focus error detection circuit 11 and the tracking error detection circuit 19, respectively.

The focus error detection signal is transmitted to the focus actuator 1 via the phase compensation circuit 28 and the amplifier circuit 191i.
2 and drives the moving coil. A servo loop serving as a focus control system is formed here to perform focus control.The focus error detection circuit 18 and the tracking error detection circuit 19 are combined and called a matrix circuit, for example. The output signal sound of adder 24.25 is calculated by Ericaro into an adder (not shown), and Pa+Pb+P
It is recorded on the first disc named e1Pd and outputs nine RF signals in purple in response to digitally encoded signals. Although not shown, this RF multiplied signal is supplied to the error signal together with the tracking error signal. As a result, the error signal processing circuit 30 generates the next signal 2-signal [phase compensation circuit 3 and amplifier circuit 32?] corresponding to the positive and negative pit string tracking errors. The signal is supplied to the radial actuator 14 via the radial actuator 14 to drive the moving coil. A servo loop serving as a tracking control system is formed here to perform tracking control.

The phase compensation circuits 29 and 31 are intended to compensate for phase delays near the cutoff frequencies of the focus control system and tracking control system that constitute the servo loop, and to prevent oscillation of each control system.

Further, the laser emitter 1) 5 is driven by a laser drive circuit 33 in such a manner that the output is substantially constant.

[Problems with background technology]

By the way, each light receiving area PD of the photodetector 17 serving as a detection device! In actuality, for example, due to various variations in the manufacturing process, there are differences in sensitivity between L to PDd, and even if the same label light is provided, it may not be possible to obtain the same level of output signal. 0This^^, in the tJg1 diagram, the focus error detection circuit 18 and the tracking error detection circuit 19 are provided with voltage sources v1 and V2, and the offset voltages are set in the state where there is no focus error or tracking error, respectively. 7'j.

However, the beam light supplied to the photodetector 17 is rarely subject to overall level fluctuation due to changes in the operating state of the laser emitter that is the light source, changes in the reflectance of the disk 11 (D), dirt on the objective lens, etc. As a result, when the amount of light beam provided to the photodetector 17 changes, the focus error detection circuit 18 and the tracking error detection circuit 19 change the offset voltage of each subtracter 21 and the tracking error detection circuit 19. , error signals may be output even though no focus error or tracking error has actually occurred.

Due to this process, an optical digital disc player equipped with the unconventional focus and tracking control system shown in Fig. 1 becomes unstable in response to fluctuations in the beam light supplied to the photodetector. There are some problems. [Object of the Invention] This first invention was made in view of the above-mentioned points, and it is possible to prevent the operation of the focus control system even if the amount of beam reflected by the disk and provided to the detection device changes. To provide a good optical digital disc player device by preventing instability and stabilizing the amount of beam light provided to a detection device to stabilize the operation of a tracking control system. 0 [Object of the Invention] This invention emits beam light tWA of a predetermined wavelength from a laser emitter onto a disc on which a digitally encoded signal obtained by encoding an information signal is recorded as a bit string, and the reflected light is emitted from a laser emitter. [Multiple light receiving units] By irradiating the next detection device, the output signal of the detection device is converted into the digitally encoded signal? At the same time, a focus error detection signal and a tracking error detection signal are generated, and the first and second signals are generated based on the output signal of the detection device in a sequential optical digital disc player. A means for deriving 1gl of light and a level adjustment for one of the first and second signals to compensate for the difference in sensitivity between the respective light receiving sections of the detection device, 1g20 means for outputting a signal difference signal t to the focus control system as a focus error detection signal; a third means for directly deriving the difference signal t between the first and second signals to the first means; 2. Difference signal of each ratio signal obtained by the method of @3? The present invention is characterized in that it includes a WJ4 means for controlling the amount of beam light fed back to the laser drive circuit driving the laser emitter and supplied to the detection device to be substantially constant.

[Embodiments of the Invention] Fig. 2 shows the main parts of an optical digital distractor player device according to the present invention. However, in FIG. 2, the same parts as in FIG.

That is, the focus error detection circuit 1 shown in FIG.
The output terminal of the adder 2o in 8 is connected to the non-inverting input terminal (+) of the adder/subtractor 22, and is connected to one input terminal of the adder 41.
The output terminal of is connected to the inverting input terminal (→) of the adder/subtractor 220, and is also connected to the inverting input terminal (→) of the operational amplifier 42 via a resistor RIk.
The output terminal is connected to the other input terminal of the adder 41, and is feedback connected to the inverting input i (→) via the variable resistor VR, 1r, and the non-inverting input terminal (+) is grounded. The operational amplifier 42, the resistor R6, and the variable resistor VR are:
It consists of an inverting amplifier with adjustable gain. The output terminal of the adder 41 corresponds to the output terminal of the focus error detection circuit 18 and is connected to the input terminal of the amplifier 290 via the phase compensation circuit 28.

At the same time, the output terminal of the adder 41 is connected to the non-inverting input terminal (+) of the subtracter 43.

The output terminal of this subtracter 43 is connected to a laser drive circuit 44 which can control the output sound of the laser emitter 15 from the outside.
In other words, in the optical digital disc player having the above-mentioned configuration, is there no focus error, no tracking error? To detect. At this time,
For example, by operating the variable resistor VR, i, the gain of the operational amplifier 42 is 1.
Adjustment is made so that the output level of the m adjustment adder 4 becomes zero. As a result, the absolute values of the respective input terminal levels of the adder 41 are equal, and it can be equivalently considered that the sensitivities of the individual light areas PDa to PDa of the photodetector 17 are approximately equal. The voltage source v2 is adjusted to offset the offset voltage of the subtracter 27.

There is no focus error on this one! 1c1
Even if the amount of light supplied to the photodetector 17 changes, the output of the adder 41 (that is, the focus error detection signal) does not change, and the oven loop gain of the focus control system that forms the multiple loops simply changes. Furthermore, the difference signal between the outputs of the adder 41 and the subtracter 22 outputted by the subtracter 43 corresponds to the change in the light intensity of the beam light provided to the photodetector 11, and is output from the control input terminal of the laser drive circuit 44. will be given negative feedback. As a result, the laser drive circuit 44 controls the laser emitter 15' so that the amount of beam light provided to the photodetector 17 is approximately constant.
(The output of the offset voltage to the output terminals of the subtracters 23 and 24 is prevented as much as possible.)
[It is something that Therefore, such an optical digital disc player is equipped with the sophisticated focus control system shown in FIG.
The playback can be performed.

Note that the present invention is not limited to the above-mentioned embodiments. For example, in the tracking error calibration circuit 19,
An inverting amplifier configured in the same manner as the operational amplifier 42° resistor RI + variable resistor VR in Fig. 2 is provided to compensate the level of each signal of P1 + Pck and Pb + Pd, so that (Pi + Pc) - (Pb + Pd). You can also strain the signals from adult cows.

It goes without saying that various other modifications and applications are possible without departing from the gist of the invention.

〔Effect of the invention〕

As detailed below, according to the present invention, even if the amount of beam reflected by the disk and provided to the detection device t changes, the operation of the focus control system can be prevented from becoming unstable, and the detection A good optical digital disc player device that stabilizes the amount of beam light provided to the device and stabilizes the operation of the tracking control system. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a focus control system and a tracking control system mounted on a conventional optical digital disc player, and FIG. 2 is a circuit diagram showing a main part of an optical digital disc player according to the present invention. 11...Disc, 12...Yanagi lens, 13...
-Focus actuator, 14...Radial actuator, 15...Laser emitter, 16...Beam splitter, 11...Photodetector, 18...Focus error detection circuit, 1g...Tracking, king Error detection circuit, 21, 22, 24.25°41...
Adder, 22, 23, 26, 277.43...Subtractor,! Ji, 31... Phase compensation circuit, 29°32...
, amplifier circuit, 3o... error signal processing circuit, 33.4
4... Laser drive circuit, 42... Operational amplifier, V,
, V... Voltage source, R7... Resistor, VR. ...Variable resistance○

Claims (1)

[Claims] A laser emitter is irradiated with a beam of a predetermined wavelength and the reflected light is sent to a plurality of light receiving sections The digital encoded signal is extracted from the output signal of the detection device, and a focus error detection signal and a tracking error detection signal are generated to perform focus control and tracking control. In the optical digital disc player device, a first detection signal is detected based on the output signal of the detection device.
and a first means for deriving a second signal, and after level adjustment is performed on either the first signal or the second signal to compensate for the sensitivity difference between the light receiving sections of the detection device. Jli2 means outputs the difference signal t between the first and second signals to the focus control system as a focus error detection signal; The difference signal between the ratio signals obtained from the means of 3 and the second and third means [the beam light amount r that is fed back to the laser drive circuit that drives the laser emitter and is provided to the detection device is approximately constant] Optical digital disc player device 0 characterized by comprising a fourth controlling means and a tether.