Coherent light generators – Particular component circuitry – Having feedback circuitry
Reexamination Certificate
1999-03-11
2002-02-05
Leung, Quyen (Department: 2881)
Coherent light generators
Particular component circuitry
Having feedback circuitry
C372S038020
Reexamination Certificate
active
06345062
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser apparatus with an improved feedback control circuit for controlling the driving of the semiconductor laser, an information recording/reproduction apparatus such as an optical disk apparatus, and an image recording apparatus such as a laser beam printer or a copying machine.
Semiconductor lasers have advantages such as an easy direct light intensity modulation, small in size, a low consumption power and a high efficiency, and therefore they are widely used in memory devices having large capacities, such as optical disk devices and laser beam printers.
However, the semiconductor laser of the current type entails drawbacks, that is, the amount of light emitted is varied, and the laser itself is easily damaged due to excessive current, for various reasons.
When a semiconductor laser is driven, the amount of light emitted from the semiconductor laser is detected, and the driven amount is negative-feedback-controlled on the basis of the result thereof, and a control circuit for stabilizing the amount of light emitted is used. Further, in the case of the optical disk device, there are great demands of a light intensity modulation of a higher accuracy and lower noise during reproduction of data, in order to achieve a larger capacity and a higher speed of data transfer.
In particular, in a recordable medium or a phase changeable medium (PC medium) capable of overwriting data, the S/N ratio of the entire system greatly depends upon optical laser noise, and therefore it is very important to suppress such noise in order to increase the recording density.
Further, in a magneto-optical medium (MO medium), the differential detection method is used for the reproduction of a signal, and therefore the influence of laser noise is less as compared to the case of the recordable medium or PC medium. However, since the reproduction signal level is extremely low, it is required that the optical laser noise should be suppressed to a certain level or less.
Under these circumstances, a wide-band type front automatic power control (APC) disclosed in, for example, “High-Precision Laser Control Method (II) in Optical Disk Apparatus”, General Meeting in Spring 1991 of the Institute of Electronics, Information and Communications Engineering, C-372 by Taguchi and Hoshino, has been proposed as a means for suppress the laser noise while using a presently available semiconductor laser as a light source of the optical disk device.
In this method, when output light from the semiconductor is irradiated onto a recording medium, light actually irradiated onto an optical disk (that is, part of the front light of the semiconductor laser) is guided to a light detector, and with use of the detection signal, the output light of the semiconductor laser is controlled. Thus, the control band can be widened, and the optical laser noise can be suppressed.
In the wide band front APC method, it is significant how wide the control band can be made as compared to the reproduction signal band. The technique of widening the control band larger than the reproduction signal band is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 4-208581, U.S. Pat. No. 5,097,473 entitled “Semiconductor Laser Apparatus” and filed by the same applicants as those of the present invention.
This semiconductor laser apparatus is equipped with an error detector for generating an error signal corresponding to a difference between an output signal from a light intensity detector for detecting the intensity of output light from the semiconductor laser, and a laser drive control signal from outside, so as to constitute a feedback control system for negative-feedback-controlling the driving current for the semiconductor laser on the basis of the error signal. Further, the semiconductor laser apparatus includes a phase compensation circuit for negative-fed back a compensation current for compensating a phase delay of the feedback control system, to an input side of the error detector.
Further, the applicant of the present invention proposed “Semiconductor Laser Apparatus, Information Recording/Reproducing Apparatus and Image Recording Apparatus” capable of dispensing with the adjustment of the CR time constant for the phase compensation of a phase compensation loop separately from the front APC loop, and imparting the variable gain function to the phase compensation amplifier (Jpn. Pat. Appln. KOKAI Publication No. 8-83948, U.S. Pat. No. 5,579,329).
FIG. 1
shows the first prior art example of the semiconductor laser apparatus using a wide band front APC circuit, which is applied to an optical disk drive apparatus.
As shown in this figure, a semiconductor device for driving a laser, is denoted by reference numeral
60
, and a semiconductor laser
1
, a monitor light receiving element
2
, a resistor element
3
and a variable resistor element
4
are provided outside the semiconductor device
50
to be connected thereto. In this example, the laser driving semiconductor device
60
has a plurality of external terminals. The semiconductor laser
1
is connected between the first external terminal
11
and the external power source, the monitor-use light receiving element
2
is connected between the second external terminal
12
and the external power, and the resistor element
3
is connected between the third external terminal
13
and the ground potential, and the variable resistor element
4
is connected between the fourth external terminal
14
and the ground potential.
The monitor-use light receiving element
2
is, for example, a pin photo-diode, having one end to which, for example, a power voltage Vcc is applied as a DC reverse voltage. The light receiving element
2
receives part of the light emission output from the semiconductor laser
1
, and generates a current corresponding to the level of the received light. The light receiving element
2
and the semiconductor laser
1
are used in the optical recording/reproducing head portion of an optical disk drive apparatus.
Next, the interior of the semiconductor device
60
for driving the laser, will now be described.
A gain controllable operation amplifier circuit (gain control amplifier: GCA)
15
has a non-reversal input terminal (+), to which a reference voltage REF is input via an input resistance Ri.
To the reversal input terminal (−) of the circuit
15
, a laser drive control signal SIG is input via an input resistance Ri. A negative feedback signal is input from the monitor-use light receiving element
2
to the circuit
15
via the second external terminal
12
, and a gain control voltage is supplied from the variable resistor element
4
via the fourth external terminal
14
, to the gain control terminal of the circuit.
A gain-fixed type control amplification circuit
16
is an operation amplification circuit having a non-reversal input terminal (+) and a reversal input terminal (−) to which output signals (differential signals) from the GCA
15
are input, and the signals are amplified.
The GCA
15
and the control amplifying circuit
16
connected to the next stage, constitute an error detection circuit for detecting an error between a laser drive control signal input and a negative feedback signal input from the monitor-use light receiving element.
A high-frequency signal generating circuit
17
is designed to generate a high frequency signal of a predetermined frequency, to be superimposed on a laser drive control signal SIG, so as to suppress laser noise caused by reflection light from the optical disk, returning to the semiconductor laser (that is, return light) during a play-back of the optical disk. The high-frequency signal is supplied to the non-reversal input terminal (+) of the GCA
15
via a coupling capacitor Cc.
A laser drive circuit
18
is designed to current-drive the semiconductor laser
1
on the basis of an output signal from the control amplifying circuit
16
. The laser drive circuit
18
is made of, for example, an NPN transistor having a base co
Nagahama Tetsuya
Taguchi Toyoki
Tazawa Masayuki
Leung Quyen
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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