Eye-safe laser navigation sensor

• US 20070230525A1
• Filed: 05/12/2006
• Published: 10/04/2007
• Est. Priority Date: 03/31/2006
• Status: Active Grant

• Current Assignee: Monterey Research, LLC (Vector Capital Corporation)
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Gibbs, Gary, Rohilla, Gajender, Sanders, Steven, Shah, Pulkit, Pancholy, Ashish
• Granted Patent: US 7,809,035 B2
• Time in Patent Office: Days
• US Class Current: 372/38.20
• CPC Class Codes: H01S 5/042 Electrical excitation ; Circuits therefor monolithically integrated laser drive components H01S5/0261
• CPC Class Codes: H01S 5/06808 by monitoring the electrical laser parameters, e.g. voltage or current

Abstract

One embodiment relates to an optical navigation apparatus which provides fault-tolerant limitation of laser output power. The apparatus includes a diode laser and a current source interconnected with the diode laser. Two independent circuits in the current source are configured to limit current flowing through the diode laser. Another embodiment relates to a method of providing fault-tolerant limitation of laser output power in an optical navigation apparatus. A first digital current limit value is converted to a first analog signal, and the first analog signal is used to limit an electrical current from a power supply connection to an anode of a diode laser. A second digital current limit value is converted to a second analog signal, and the second analog signal is used to limit an electrical current from a cathode of the diode laser to a ground connection. Other embodiments are also disclosed.

Claims

1. An optical navigation apparatus providing fault-tolerant limitation of laser output power, the apparatus comprising:

a diode laser; and

a current source interconnected with the diode laser; and

two independent circuits in the current source for limiting current flowing through the diode laser.

2. The apparatus of claim 1, wherein the current source is integrated onto a single silicon die.

3. The apparatus of claim 2, further comprising:

two independent memory registers integrated into the current source, wherein the two independent memory registers are programmed to hold digital current limit data.

4. The apparatus of claim 3, further comprising:

two independent digital-to-analog (D/A) converters integrated into the current source, wherein the two independent D/A converters are each configured to convert the digital current limit data to an analog current limit signal.

5. The apparatus of claim 4, further comprising:

two independent current limiter circuits integrated into the current source, wherein the two current limiter circuits are configured to be controlled by the analog current limit signals.

6. The apparatus of claim 5, wherein a first current limiter circuit is configured between a supply voltage and an anode of the diode laser so as to limit a current output from the current source.

7. The apparatus of claim 6, wherein a second current limiter circuit is configured between a ground connection and a cathode of the diode laser so as to limit a current return to the current source.

8. The apparatus of claim 5, further comprising:

two independent supply voltage sensors integrated into the current source, wherein the two supply voltage sensors are configured to monitor changes in a supply voltage of the current source; and

two independent compensation circuits controlled by output signals from the two supply voltage sensors.

9. The apparatus of claim 8, wherein each compensation circuit is configured to modify the digital current limit data read from an associated memory register and to provide the voltage-compensated digital data to an associated D/A converter.

10. The apparatus of claim 5, further comprising:

two independent temperature sensors integrated into the current source, wherein the two temperature sensors are configured to monitor changes in an operating temperature; and

two independent compensation circuits controlled by output signals from the two temperature sensors.

11. The apparatus of claim 10, wherein each compensation circuit is configured to modify the digital current limit data read from an associated memory register and to provide the temperature-compensated digital data to an associated D/A converter.

12. The apparatus of claim 5, further comprising:

two independent supply voltage sensors integrated into the current source, wherein the two supply voltage sensors are configured to monitor changes in a supply voltage of the current source; and

two independent temperature sensors integrated into the current source, wherein the two temperature sensors are configured to monitor changes in an operating temperature; and

two independent compensation circuits, wherein each compensation circuit is controlled by output signals from associated voltage and temperature sensors.

13. The apparatus of claim 1, wherein the laser output power does not exceed a predetermined power limit over a range of anticipated operating conditions even with occurrence of a single fault event.

14. A method of providing fault-tolerant limitation of laser output power in an optical navigation apparatus, the method comprising:

converting a first digital current limit value to a first analog signal;

using the first analog signal to limit an electrical current from a power supply connection to an anode of a diode laser;

converting a second digital current limit value to a second analog signal; and

using the second analog signal to limit an electrical current from a cathode of the diode laser to a ground connection.

15. The method of claim 14, wherein said converting and using steps are performed with circuitry integrated onto a single silicon die.

16. The method of claim 14, further comprising:

sensing a supply voltage with a first sensor;

compensating for changes in the supply voltage by adjusting the first digital current limit value based on output from the first sensor;

sensing the supply voltage with a second sensor which is independent of the first sensor; and

compensating for changes in the supply voltage by adjusting the second digital current limit value based on output from the second sensor.

17. The method of claim 14, further comprising:

sensing a temperature with a first sensor;

compensating for changes in the temperature by adjusting the first digital current limit value based on output from the first sensor;

sensing the temperature with a second sensor which is independent of the first sensor; and

compensating for changes in the temperature by adjusting the second digital current limit value based on output from the second sensor.

18. An integrated circuit configured to provide fault-tolerant limitation of laser output power in an optical navigation apparatus, the integrated circuit comprising:

circuit means for converting a first digital current limit value to a first analog signal;

circuit means for using the first analog signal to limit an electrical current from a power supply connection to an anode of a diode laser;

circuit means for converting a second digital current limit value to a second analog signal; and

circuit means for using the second analog signal to limit an electrical current from a cathode of the diode laser to a ground connection.

19. The integrated circuit of claim 18, further comprising:

a first sensor circuit for sensing a supply voltage;

circuit means for compensating for changes in the supply voltage by adjusting the first digital current limit value based on output from the first sensor circuit;

a second sensor circuit for sensing the supply voltage which is independent of the first sensor circuit; and

circuit means for compensating for changes in the supply voltage by adjusting the second digital current limit value based on output from the second sensor circuit.

20. The integrated circuit of claim 18, further comprising:

a first sensor for sensing a temperature;

circuit means for compensating for changes in the temperature by adjusting the first digital current limit value based on output from the first sensor;

a second sensor for sensing the temperature which is independent of the first sensor; and

circuit means for compensating for changes in the temperature by adjusting the second digital current limit value based on output from the second sensor.