JPH01211326A - Actuator driving circuit - Google Patents

Abstract

PURPOSE:To perform tracking at the center of a track so as to prevent decline of C/N by correcting the offset produced in the quantity of the light which is split by the optical beam at the center of the track and projected on a photodetector element. CONSTITUTION:Since tracking error signals cut grooves at the time of track jumping, the maximum and minimum (negative maximum) values are produced. The maximum and minimum values are respectively held by a peak holding circuit 4 and inversional amplifier circuit 6 until the next track jump controlling signal comes. Then the values are inputted to a differential amplifier circuit 7 and a mean value is obtained. The differential between the mean value and the tracking error signals is taken at a differential amplifier circuit 8 and a servo is actuated so as to make the output of the amplifier circuit 8 zero. Therefore, even when a tracking actuator operates within the range of <=+ or -0.1mm from the center of a movable section, tracking can be performed at the center of a track and decline of C/N is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a tracking actuator and drive circuit for optical disk drives and magneto-optical disk drive devices used for document files, data files, and the like.

2. Description of the Related Art Conventionally, this type of actuator drive circuit has had a configuration as shown in FIG. In FIG. 2, 21 is a photodetection element, 22 is an amplifier circuit that converts the output current from the photodetection element 21 into voltage and amplified it, and 23 is a differential amplifier circuit that takes the difference between the outputs from the two amplifier circuits 22. 24 is a phase compensation circuit that performs phase compensation of the differential output; 25 is a switch circuit that switches whether the phase compensation output is a track jump signal according to a track jump control signal; and 26 is a driver that amplifies the current of the output from the switch circuit 25. circuit,
27 is a tracking actuator.

The operation of the actuator drive circuit configured as described above will be described below.

The light irradiated onto the disk by the optical head is diffracted by the tracking groove, passes through the optical head again, and is irradiated onto the two-divided photodetecting element 21. The photodetector element 21 converts the amount of light into a current. The converted current is converted into a voltage by the amplifier circuit 22 and further amplified. The respective amplified voltages from the two divided photodetection elements 21 are input to a differential amplifier circuit 23, and a differential output (this is called a tracking error signal) is obtained. A phase compensation circuit 24 performs phase compensation on this tracking error signal. Since the grooves on the disk are cut in a spiral shape, if you try to trace the same track, it is necessary to perform a track jump to return to the original track once every revolution. A switch circuit 26 switches between the output from the phase compensation circuit and the track jump signal, and the switching is performed in accordance with the track jump control signal. Furthermore, the output from the switch circuit 26 is current-amplified by the driver circuit 26 to drive the tracking actuator 27. When a track jump occurs, a current flows through the tracking actuator to return one track to the original position by the switch circuit 26, but otherwise the differential amplifier circuit 2
The servo is applied so that the output from 3 becomes zero.

Problems to be Solved by the Invention However, with the above configuration, when the tracking actuator 27 operates near the center of the movable part, the amount of light to the two divided photodetecting elements 21 becomes equal at the center of the track. However, if the moving part is operating between ±0.1 or more from the center of the moving part, the end of the objective lens will be used, resulting in vignetting of the light, and the light detection will be divided into two at the center of the track. The amount of light to the element 21 is no longer equal, and off-seratra occurs. Since the servo works so that the output from the differential amplifier circuit 23 is zero, that is, the amount of light to the two divided photodetecting elements 21 is equal, tracking occurs at a point away from the center of the track, causing a large drop in C/N. However, the servo gain becomes small and tracking is lost.

In view of the above problems, the present invention provides tracking at the center of the track even at a position of ±0.1■ or more from the center of the movable part of the tracking actuator, reducing the drop in C/H, and increasing the tracking range. The present invention provides a complete actuator drive circuit that can be used.

Means for Solving the Problems For this purpose, the present invention provides a first means for detecting the maximum and minimum values of a tracking error signal at the time of a track jump, and a second means for calculating the average value of the maximum and minimum values. and third means for using a difference signal between the tracking error signal and the average value as a new tracking error signal.

Effect: With this configuration, even if the tracking actuator operates within a range of, for example, ±0.5 from the movable part, tracking is performed at the center of the track, making it possible to reduce the drop in G/H.

EXAMPLES Below, the actuator drive circuit of the present invention will be described with reference to the drawings.

FIG. 1 shows a circuit diagram of an actuator drive circuit in one embodiment of the present invention. In Fig. 1, 1 is a divided photodetection element, 2 is an amplifier circuit that converts the output current from the photodetection element 1 into voltage and amplifies it, and 3 is a difference between the output voltages from the two amplifier circuits 2. a dynamic amplifier circuit, 5 is a peak hold circuit having a hold capacitor 6 that holds the peak value of the output (tracking error signal) from the differential amplifier circuit and clears it with a track jump control signal; 6 is a peak hold circuit that inverts the tracking error signal; 7 is a differential amplifier circuit that takes the difference between the outputs from the two peak hold circuits 4 and outputs the average; 8 is a differential amplifier circuit that inputs the tracking error signal to the differential amplifier circuit 7; A differential amplifier circuit that takes the differential output of
9 is a phase compensation circuit that performs phase compensation; 1o is a switch circuit that switches between the output from the phase compensation circuit 9 and the track jump signal according to a track jump control signal; 11 is a driver circuit that performs current amplification; and 12 is a tracking actuator. .

The operation of the actuator drive circuit configured as above will be described below.

The light irradiated onto the disk by the optical head undergoes diffraction by the tracking groove, passes through the optical head again, irradiates the divided photodetection element 1, is converted into a current, and is further converted into voltage and amplified by the amplifier circuit 2. Ru. 2
The outputs from the two amplifier circuits 2 are input to the differential amplifier circuit 3, and a tracking error signal is obtained. The grooves on the disk are cut in a spiral shape, so if you try to trace the same track, a track jump is performed to return the track to its original position once every revolution. This track jump is performed by the switch circuit 1 by the track jump control signal.
This is done by switching to 0 and giving a track jump signal. The tracking error signal at track jump is
Maximum and minimum values (negative maximums) result from crossing the groove. This maximum value is held by the peak hold circuit 4 that charges and discharges the hold capacitor 6, and the minimum value is held by the inverting amplifier circuit 6 and the peak hold circuit 4 until the next track jump control signal arrives. If it does, it will be cleared, and the next maximum and minimum values will be captured and held. If these maximum and minimum values are input to a differential amplifier circuit 7 with a gain of 0.6, an average value can be obtained.

This average value is equal to the DC offset of the tracking error signal that occurs when the amount of light incident on the divided photodetecting elements differs even if the original beam is at the center of the track. Therefore, if the average value and the tracking error signal are differentiated by the differential amplifier circuit 8, the DC offset can be canceled, and if the light beam is at the center of the track, the output of the differential amplifier circuit 8 will be zero. This current is passed through the phase compensation circuit 9 and the switch circuit 10 and is amplified by the driver circuit 11 to drive the tracking actuator 12. Since the servo operates so that the output of the differential amplifier circuit 8 becomes zero, tracking will occur at the center of the track even if the tracking actuator operates within a range of ±0.1 mm or more from the center of the movable part.

As a result, a tracking accuracy of ±0.1 μm and a C/N drop of 0.3 dB or less were obtained within the range of ±0.5 mm.

Effects of the Invention As described above, the present invention corrects an offset in the amount of light irradiated to the photodetecting element divided by the light beam at the center of the track, thereby increasing the tracking range of the tracking actuator to, for example, 10.5 m. By increasing the size of the disc, it is no longer necessary to correct the eccentricity of the disk using a linear motor, and an inexpensive stepping motor can be used, which has a significant effect.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an actuator drive circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional actuator drive circuit. 4...Peak hold circuit, 6...Hold capacitor, 6...Inverting amplifier circuit, 7.
...Differential amplifier circuit, 8...Differential amplifier circuit.

Claims (5)

[Claims] (1) A first means for detecting the maximum value and minimum value of the tracking error signal at the time of a track jump, a second means for calculating the average value of the maximum value and the minimum value, and the tracking error signal and the average value. an actuator drive circuit comprising third means for using a difference signal between the two values as a new tracking error signal. (2) The first means has a hold capacitor which inputs the tracking error signal and holds the maximum value of the tracking error signal or a value similar to the maximum value as an output until the next track jump as a means for detecting the maximum value. An actuator drive circuit according to claim 1, comprising a peak hold circuit. (3) The first means uses an inverting amplifier circuit that inputs the tracking error signal as a means for detecting the minimum value, and an inverting amplifier circuit that inputs the output of the inverting amplifier circuit and detects the minimum value according to the maximum value of the output of the inverting amplifier circuit until the next track jump. The actuator drive circuit according to claim 1 or 2, further comprising a peak hold circuit that holds the value as an output. (4) The second means uses a differential or summing amplifier circuit that inputs the maximum value or a value similar to the maximum value and the minimum value or a value similar to the minimum value and outputs the average value or a value similar to the average value. An actuator drive circuit according to claim 1. (5) The third means is provided with a differential or summing amplifier circuit that receives the tracking error signal and the average value or a value similar to the average value and outputs the new tracking error signal as claimed in claim 1. Actuator drive circuit described in section.