Open loop laser power control for optical navigation devices and optical systems
View Patent ↗A current output of a drive signal, modulated between two current settings, is applied to a laser diode, e.g. VCSEL. The settings are selected such that laser diode's power output meets the average power and peak power limits of the eye safety standards. The drive signal having a duty cycle toggling between the two settings. The duty cycle is selected such that the average and peak power limits are met for the given upper current setting. The drive circuit may include an analog modulator or digital analog converter (DAC) for maintaining the lower and upper current settings. When the drive circuit is implemented as an integrated circuit, the DAC may be incorporated into the IC. The sensitivity of the DAC is selected to maintain the desired lower and upper current settings.
1. A system comprising:
a drive circuit configured to provide a drive signal modulated between a minimum current setting and a maximum current setting at a desired duty cycle; and
a laser configured to receive the drive signal and generate an output, wherein a difference between the maximum current setting and the minimum current setting is such that output power of the laser can be controlled by the drive signal within about 2 percent of a desired output power over temperature.
2. A system, as defined in claim 1 , wherein the laser is a semiconductor-based laser.
3. A system, as defined in claim 2 , wherein the semiconductor-based laser is selected from a group that includes vertical cavity surface emitting lasers, edge emitting laser diodes, super-resonant cavity light emitting diodes (LEDs), and high efficiency LEDs.
4. A system, as defined in claim 1 , the drive circuit further including a digital-to-analog converter.
5. A system, as defined in claim 1 , wherein the output power of the laser is below a select average power limit.
6. A system, as defined in claim 1 , wherein output power of the laser is below a select peak power limit.
7. A system, as defined in claim 1 , wherein the minimum current setting and the maximum current setting are adjacent current settings.
8. A system, as defined in claim 5 , wherein the select average power limit corresponds to at least a minimum operative level to project and receive a reflected signal.
9. An optical navigation device comprising:
an optical mouse sensor that includes a drive circuit configured to provide a drive signal having a current output modulated between a minimum current setting and a maximum current setting at a desired duty cycle; and
a laser configured to receive the drive signal and generate an output, wherein a difference between the maximum current setting and the minimum current setting is such that output power of the laser can be controlled by the drive signal within about 2 percent of a desired output power over temperature.
10. An optical navigation device, as defined in claim 9 , wherein the laser is a vertical cavity surface emitting laser.
11. An optical navigation device, as defined in claim 9 , the drive circuit further including a digital-to-analog converter.
12. An optical navigation device, as defined in claim 9 , wherein the output power of the laser is below a select average power limit.
13. An optical navigation device, as defined in claim 9 , wherein the drive signal output power of the laser is below a select peak power limit.
14. An optical navigation device, as defined in claim 9 , wherein the minimum current setting and the maximum current setting are adjacent current settings.
15. An optical navigation device, as defined in claim 12 , wherein the select average power limit corresponds to at least a minimum operative level to project and receive a reflected signal.