Coherent light generators – Particular component circuitry – Controlling current or voltage to laser
Reexamination Certificate
2000-08-18
2003-03-04
Ip, Paul (Department: 2828)
Coherent light generators
Particular component circuitry
Controlling current or voltage to laser
C372S038080
Reexamination Certificate
active
06529536
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a laser drive circuit and a recording apparatus using this laser drive circuit. More specifically, the present invention relates to an optical disc recording and reproducing apparatus for compact discs (CD-R (Recordable)/CD-RW (Read Write)), digital versatile discs (DVD-RAM (Random Access read write Memory)), magnet-optical (MO) discs, or other discs to which data can be written, as well as a laser drive circuit applied to this apparatus.
A known laser drive circuit applied to an apparatus of this kind is described, for example, in Japanese Patent Publication No. 8-3904 (hereafter referred to as a “conventional example”).
FIG. 1
shows the laser drive circuit described in the conventional example. The laser drive circuit
100
comprises an operation amplifier (hereafter referred to as an “OP amplifier”)
101
, an inverter circuit
102
having complementary output ends, PNP transistors
103
,
104
,
105
, a resistor
106
, a power terminal
110
to which a power supply Vcc is supplied, an input end
111
to which a setting voltage Vc is supplied for setting a drive current I
LD
, a terminal
112
to which a drive pulse signal CP for recording is supplied, and a terminal
113
having a semiconductor laser
114
connected thereto.
The setting voltage Vc supplied to the input end
111
is supplied to a non-inverted input end of the OP amplifier
101
. Then, a base voltage of the PNP transistor
103
is controlled depending on the setting voltage Vc. A constant current Id output from a collector of the transistor
103
is supplied to an emitter of each of the PNP transistors
104
,
105
, which constitute a current switch.
In addition, the drive pulse signal CP supplied to the terminal
112
is supplied to the inverter circuit
102
. Complementary output signals from the inverter circuit
102
are supplied to corresponding bases of the transistors
104
and
105
. When the drive pulse signal CP is at a high level, an output signal from the inverter
102
turns on the transistor
105
. This causes the constant current Id to be supplied to the semiconductor laser
114
through the terminal
113
. On the other hand, when the drive pulse signal CP is at a low level, the output signal from the inverter circuit
102
turns on the transistor
104
. This causes the constant current Id to flow to the ground.
In the laser drive circuit
100
in the above described conventional example, however, the constant current Id flows to the transistor
104
or
105
whether the drive pulse signal CP is at the high or low level. Normally, a drive current of 100 mA or higher is required for the semiconductor laser
114
during recording. The laser drive circuit
100
constantly consumes a current of 100 mA or higher. As a result, this circuit disadvantageously consumes a high current.
In particular, if the laser drive circuit
100
is located near the semiconductor laser
114
, heat generated by the laser drive circuit
100
rises an operating temperature of the semiconductor laser
114
. This results in a further increase in the drive current for the semiconductor laser
114
, which is a serious problem.
On the other hand, optical disc recording and reproducing apparatuses are required to record data at a high speed. The laser drive circuit
100
in the conventional example, however, is constructed using the PNP transistors
103
,
104
, and
105
. Accordingly, this circuit cannot essentially meet this requirement easily.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to provide a laser drive circuit that consumes less current and that can still operate at a high speed, as well as a recording apparatus using this laser drive circuit.
To attain the above object, according to a first aspect of the present invention, there is provided a laser drive circuit comprising a drive current source comprising a MOS transistor to generate a drive current depending on a setting current, a switch comprising a MOS transistor to supply the drive current supplied by the drive current source to a semiconductor laser, in response to a drive signal, and a stabilizing circuit connected to the drive current source to stabilize the drive current when the switch is turned on or off.
According to a second aspect of the present invention, there is provided a laser drive circuit comprising a drive current source comprising a MOS transistor to generate a drive current depending on a setting current, a control circuit configured to detect the setting current to control it depending on a setting voltage, and a switch comprising a MOS transistor to supply the drive current supplied by the drive current source to a semiconductor laser, in response to a drive signal.
According to a third aspect of the present invention, there is provided a recording apparatus comprising a drive circuit configured to generate a drive current for recording depending on a setting voltage for recording, and a semiconductor laser to which the drive current from the drive circuit is supplied, the drive circuit comprising a drive current source comprising a MOS transistor to generate the drive current depending on a setting current corresponding to the setting voltage, and a switch comprising a MOS transistor to supply the drive current supplied by the drive current source to the semiconductor laser, in response to a drive signal.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
REFERENCES:
patent: 4868482 (1989-09-01), O'Shaughnessy et al.
patent: 5317206 (1994-05-01), Hanibuchi et al.
patent: 5514989 (1996-05-01), Soto et al.
patent: 5796767 (1998-08-01), Aizawa
patent: 5859862 (1999-01-01), Hikasa et al.
Ip Paul
Kabushiki Kaisha Toshiba
Nguyen Tuan M
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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