Coherent light generators – Particular component circuitry – For driving or controlling laser
Reexamination Certificate
2000-01-28
2001-11-20
Font, Frank G. (Department: 2877)
Coherent light generators
Particular component circuitry
For driving or controlling laser
C372S038010, C372S038070, C372S038040, C330S260000, C330S308000
Reexamination Certificate
active
06320890
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a driving circuit for a semiconductor laser which is applied to an optical disk recording/reproducing apparatus using a recordable compact disk (CD-R), digital versatile disk (DVD-RAM), magneto-optic disk (MO), for example.
As the laser driving circuit applied to the above type of apparatus, an automatic power control (APC) system and automatic current control (ACC) system are provided.
FIG. 12
shows a conventional apparatus of APC system used for an MO, for example. The apparatus includes a laser driving circuit
101
, a laser diode (LD)
102
constructed by a semiconductor laser, lenses
103
,
105
,
106
,
108
constructing an optical system, a beam splitter
104
, a 4-segment sensor
107
, for example, for detecting reflected light from an optical disk
110
at the data readout time, and a photodiode
109
for detecting an output signal from the laser diode
102
and feeding the same back to the laser driving circuit
101
. The laser driving circuit
101
controls the amount of emission light of the laser diode
102
according to a signal supplied from the photodiode
109
.
FIG. 13
shows a conventional apparatus of ACC system used for CD-R or DVD-RAM, for example. The apparatus includes a laser driving circuit
111
, a laser diode (LD)
112
, lenses
113
,
115
,
116
constructing an optical system, a beam splitter
114
, a 4-segment sensor
117
, for example, for detecting reflected light from an optical disk
119
at the data readout time, a photodiode
118
used as a photodetector for detecting an output light amount of the laser diode
112
, an amplifier
120
for amplifying an output signal of the photodiode
118
and a digital signal processing circuit
121
for processing an output signal of the amplifier
120
and supplying the processed signal to the laser driving circuit
111
. The digital signal processing circuit
121
includes an analog/digital converter (A/D)
121
a
for converting an output signal of the amplifier
120
into a digital signal, a microprocessor unit (MPU)
121
b
for processing an output signal of the analog/digital converter
121
a,
and a digital/analog converter (D/A)
121
c
for converting an output signal of the microprocessor unit
121
b
into an analog signal. The laser driving circuit
111
controls the amount of emission light of the laser diode
112
according to a signal supplied from the digital signal processing circuit
121
by use of a current value thereof.
In the case of APC system shown in
FIG. 12
, a plurality of pulse signals are generated for each pit in order to form pits of good shape in the optical disk. The laser diode is driven by the pulse signals. Therefore, the laser diode
102
is driven by a high-frequency pulse signal. As a result, it is required for the photodiode
109
which monitors the light emission output of the laser diode
102
to have a wide-band characteristic of 500 MHz, for example. Further, a high-precision lens is used as the lens
108
for guiding the laser light to the photodiode
109
. On the other hand, in the case of ACC system, the high-speed response in comparison with the APC system is not required. Therefore, the photodetector and optical system can be made simple in construction.
However, in the conventional ACC system shown in
FIG. 13
, in the laser driving circuit
111
constructed by a semiconductor integrated circuit, variations occur in resistances of resistors constructing the circuit. Further, the resistance fluctuates depending on the temperature. In addition, the transistor characteristic also fluctuates depending on the temperature. Therefore, it is difficult to stabilize the laser output with high precision.
BRIEF SUMMARY OF THE INVENTION
This invention has been made in order to solve the above problem and an object of this invention is to provide a laser driving circuit capable of stabilizing the laser output with high precision.
The above object can be attained by a laser driving circuit comprising: a first amplifier for comparing an input signal which controls a light emission intensity of a semiconductor laser with a monitor signal obtained by monitoring a driving current of the semiconductor laser and effecting the control operation to make the input signal and the monitor signal substantially equal to each other; a second amplifier connected to an output terminal of the first amplifier; an adder circuit for adding together output signals of the first and second amplifiers; a driving current generating circuit having an input terminal supplied with an output signal of the adder circuit and an output terminal configured to be connected to the semiconductor laser, for generating a driving current of the semiconductor laser according to the output signal of the adder circuit; and a terminal to which a resistor for detecting the driving current output from the driving current generating circuit and generating the monitor signal is connected.
Further, a laser driving circuit comprising: a first amplifier for comparing an input signal which controls a light emission intensity of a semiconductor laser with a feedback signal obtained by feeding back a driving current of the semiconductor laser and effecting the control operation to make the input signal and the feedback signal substantially equal to each other; a second amplifier connected to an output terminal of the first amplifier; an adder circuit for adding together output signals of the first and second amplifiers; a driving current generating circuit supplied with an output signal of the adder circuit, for generating the driving current of the semiconductor laser, at least part of the driving current being fed back to the first amplifier as the feedback signal; and a resistor connected to an input terminal of the first amplifier, for detecting the feedback signal fed back from the driving current generating circuit.
In addition, a laser driving circuit comprising: at least two converting circuits for converting at least two input signals which control a light emission intensity of a semiconductor laser to currents for generating a driving current used for driving the semiconductor laser; a current mirror circuit having an input terminal supplied with output signals of the at least two converting circuits; a current switch circuit connected to an output terminal of the current mirror circuit, for eliminating a current which is unnecessary for an operation mode of the semiconductor laser from an output signal of the current mirror circuit according to the operation mode of the semiconductor laser to generate a control current; and a driving current generating circuit having an input terminal supplied with the control current and an output terminal configured to be connected to the semiconductor laser, for generating the driving current of the semiconductor laser according to the control current.
Further, a laser driving circuit comprising: at least two converting circuits for converting at least two input signals which control a light emission intensity of a semiconductor laser to currents for generating a driving current used for driving the semiconductor laser; a current switch circuit connected to each output terminal of the at least two converting circuits, for eliminating a current which is unnecessary for an operation mode of the semiconductor laser from sum of output signals of the at least two converting circuits according to the operation mode of the semiconductor laser to generate a control current; and a driving current generating circuit having an input terminal supplied with the control current and an output terminal configured to be connected to the semiconductor laser, for generating the driving current of the semiconductor laser according to the control current.
According to the laser driving circuit of this invention, the laser output can be stabilized with high precision without being influenced by fluctuations in the resistances of the internal circuit and variations in the resistances due to a temperature change.
Additional objects and advantages
Font Frank G.
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Rodriguez Armando
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