Driver circuit for semiconductor light-emitting device
AssigneeFuji Photo Film Co., Ltd.
InventorTakashi Shoji
Life of this patent
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Abstract
A driver circuit for driving a semiconductor light-emitting device such as a semiconductor laser includes a voltage-controlling amplifier for controlling a light-emitting current which enables the semiconductor light-emitting device to emit light. The output voltage of the voltage-controlling amplifier is dependent on a light-quantity command voltage signal applied thereto. Since the light-emitting current can be directly varied by the voltage-controlling amplifier, the quantity of the emitted light can vary with a sufficiently fast response to follow the light-quantity command signal. The quantity of the emitted light is maintained at the level of the light-quantity command signal under feedback control by a current-controlling amplifier.
Claims7
A driver circuit for a semiconductor light-emitting device, comprising:
- (i) a first current path comprising a first resistor having one end kept at a predetermined voltage level, a semiconductor light-emitting device having an anode connected to the other end of said resistor, a second resistor having one end connected to the cathode of said semiconductor light-emitting device, and a voltage-controlling amplifier having an output terminal connected to the other end of said second resistor;
- (ii) a second current path comprising said first resistor, a third resistor having one end connected to a junction between said other end of said first resistor and said anode of said semiconductor light-emitting device, and a current-controlling amplifier having an output terminal connected to the other end of said third resistor;
- (iii) a light detector for monitoring the intensity of light emitted from said semiconductor light-emitting device;
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- (iv) a feedback path connecting an output terminal of said light detector to an input terminal of said current-controlling amplifier;
- (v) said voltage-controlling amplifier drawing a current which enables said semiconductor light-emitting device to emit light so that an output voltage of said voltage-controlling amplifier is of a prescribed value dependent on an input signal applied to the voltage-controlling amplifier;
- (vi) said current-controlling amplifier drawing a current corresponding to the difference between an output signal applied from said light detector to said current-controlling amplifier and a reference signal applied to the current-controlling amplifier so that said intensity of light is maintained at a prescribed intensity level.
A driver circuit for a semiconductor light-emitting device, comprising:
- (i) a first current path comprising a first resistor having one end kept at a predetermined voltage level, a semiconductor light-emitting device having a cathode connected to the other end of said resistor, a second resistor having one end connected to the anode of said semiconductor light-emitting device, and a voltage-controlling amplifier having an output terminal connected to the other end of said second resistor;
- (ii) a second current path comprising said first resistor, a third resistor having one end connected to a junction between said other end of said first resistor and said cathode of said semiconductor light-emitting device, and a current-controlling amplifier having an output terminal connected to the other end of said third resistor;
- (iii) a light detector for monitoring the intensity of light emitted from said semiconductor light-emitting device;
- and
- (iv) a feedback path connecting an output terminal of said light detector to an input terminal of said current-controlling amplifier;
- (v) said voltage-controlling amplifier issuing a current which enables said semiconductor light-emitting device to emit light so that an output voltage of said voltage-controlling amplifier is of a prescribed value dependent on an input signal applied to the voltage-controlling amplifier;
- (vi) said current-controlling amplifier issuing a current corresponding to the difference between an output signal applied from said light detector to said current-controlling amplifier and a reference signal applied to the current-controlling amplifier so that said intensity of light is maintained at a prescribed intensity level.
Dependencies are inferred from the claim text.