# US 8,541,733 B2 · Laser light detection circuit

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- Number: US 8,541,733 B2
- Document ID: US8541733B2
- Status: Granted
- Kind: B2
- Application number: 13/087,101
- Filed: 2011-04-14
- Published: 2011-10-20
- Granted: 2013-09-24
- Earliest claimed: 2010-04-16
- Assignees: ON Semiconductor Trading, Ltd.
- Applicants: Rui Kurihara; Takahiro Kawashima
- Inventors: Rui Kurihara; Takahiro Kawashima
- Web page: https://patentgrep.com/patent/US8541733B2

## CPC

- G11B 7/126: Circuits, methods or arrangements for laser control or stabilisation
- G11B 7/005: Reproducing (G11B7/0065 takes precedence)
- H01S 5/06832: {Stabilising during amplitude modulation}
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL

## Abstract

The invention provides a laser light detection circuit that prevents a peak output occurring when the circuit switches between the operation stop mode and the operation mode so as to prevent the breakdown or malfunction of the next-connected circuit. A laser light detection circuit has a differential amplifier that amplifies and outputs a signal corresponding to the intensity of laser light, a drive transistor having a base to which the output of the differential amplifier is applied, a second constant-current source connected to the emitter of the drive transistor, an output transistor having a base connected to the emitter of the drive transistor, a bypass transistor connected between the emitter of the drive transistor and the ground, and a control circuit. The control circuit forms a bypass current route from the second constant-current source to the ground through the bypass transistor by turning on the bypass transistor when the circuit switches from the operation stop mode to the operation mode.

## Claims

### Claim 1

A laser light detection circuit comprising:
an amplifier amplifying an inputted signal corresponding to intensity of laser light and outputting the amplified signal;
a first transistor having an input terminal to which the signal amplified by the amplifier is applied;
a constant-current source connected to an output terminal of the first transistor;
a second transistor having an input terminal connected to the output terminal of the first transistor;
a bypass transistor connected between the output terminal of the first transistor and the ground; and
a control circuit controlling the constant-current source and the bypass transistor so as to form a bypass current route from the constant-current source to the ground through the bypass transistor by starting the operation of the constant-current source and turning on the bypass transistor when the circuit switches from an operation stop mode to an operation mode.

### Claim 2 (depends on 1)

The laser light detection circuit of claim 1, wherein the control circuit turns on the bypass transistor before the start of the operation of the constant-current source.

### Claim 3 (depends on 1)

The laser light detection circuit of claim 1, wherein the control circuit controls the constant-current source and the bypass transistor so as to form the bypass current route from the constant-current source to the ground through the bypass transistor by stopping the operation of the constant-current source and turning on the bypass transistor when the circuit switches from the operation mode to the operation stop mode.

### Claim 4 (depends on 1)

The laser light detection circuit of claim 1, wherein the control circuit turns on the bypass transistor before the stop of the operation of the constant-current source.

### Claim 5 (depends on 1)

The laser light detection circuit of claim 1, further comprising a light receiving element receiving laser light and generating a current corresponding to intensity of the received laser light, and a current voltage conversion circuit converting the current generated by the light receiving element to a voltage signal and outputting the voltage signal, wherein the voltage signal outputted by the current voltage conversion circuit is inputted to the amplifier.

### Claim 6 (depends on 1)

The laser light detection circuit of claim 1, wherein the control circuit comprises a power control signal generation circuit generating a power control signal, a bias signal generation circuit generating a bias signal for controlling the constant-current source in response to the power control signal and a switch control circuit for controlling the bypass transistor in response to the power control signal.

### Claim 7

A laser light detection circuit comprising:
a light receiving element receiving laser light and generating a current corresponding to intensity of the received laser light;
a current voltage conversion circuit converting the current generated by the light receiving element to a voltage signal and outputting the voltage signal;
an amplifier amplifying the voltage signal outputted by the current voltage conversion circuit and outputting the amplified voltage signal;
a first constant-current source supplying an operation current to the amplifier;
a first transistor having a base to which the voltage signal amplified by the amplifier is applied;
a second constant-current source connected to an emitter of the first transistor;
a second transistor having a base connected to the emitter of the first transistor;
a bypass transistor connected between the emitter of the first transistor and the ground; and
a control circuit controlling the first and second constant-current sources and the bypass transistor so as to form a bypass current route from the second constant-current source to the ground through the bypass transistor by starting the operations of the first and second constant-current sources and turning on the bypass transistor for a predetermined period when the circuit starts operating.

### Claim 8 (depends on 7)

The laser light detection circuit of claim 7, wherein the control circuit turns on the bypass transistor before the start of the operations of the first and second constant-current sources.

### Claim 9 (depends on 7)

The laser light detection circuit of claim 7, wherein the control circuit comprises a power control signal generation circuit generating a power control signal, a bias signal generation circuit generating a bias signal for controlling the first and the second constant-current sources in response to the power control signal and a switch control circuit for controlling the bypass transistor in response to the power control signal.