Circuits and methods for calibrating actuator displacement
View Patent ↗Embodiments of the present invention include circuits and methods for calibrating position displacement in a voltage controlled actuator. In one embodiment, a calibration circuit comprises an actuator having a control terminal for receiving a programmable control voltage to set a displacement, a switch that selectively decouples said programmable voltage from said control terminal and couples a reference current to said control terminal when the control terminal is decoupled from said control voltage, a comparator that senses a voltage difference between said control voltage and said control terminal, and a timer coupled to an output of the comparator. The timer measures a time period required to increase the control terminal voltage. The capacitance of the actuator may be determined and used to calibrate the position of the actuator.
1. A calibration circuit comprising:
a control terminal of an actuator configured to receive a control voltage to set a displacement of the actuator;
a switch that selectively decouples said control voltage from said control terminal in response to a first signal;
wherein the control terminal is further configured to receive a reference current when the control terminal is decoupled from said control voltage;
a comparator that senses a voltage difference between a voltage on said control terminal and the control voltage when the control terminal is decoupled from said control voltage; and
a timer coupled to an output of the comparator,
wherein the timer measures a time period between a point in time when the reference current is activated and a point in time when the voltage difference increases to a threshold.
2. The circuit of claim 1 wherein said time period is used to determine said the position of the actuator.
3. The circuit of claim 1 further comprising a controller for setting the control voltage and receiving timing information from the timer.
4. The circuit of claim 3 further comprising a memory coupled to said controller, wherein said controller retrieves calibration factors from said memory to determine said position of the actuator.
5. The circuit of claim 1 wherein said timer is a counter.
6. The circuit of claim 1 wherein the comparator is enabled after a settling period associated with said decoupling.
7. A method of calibrating actuator displacement comprising:
providing a control voltage to a control terminal of an actuator to set a displacement of the actuator;
selectively decoupling said control voltage from said control terminal in response to a first signal;
providing a reference current to said control terminal when the control terminal is decoupled from said control voltage;
comparing a voltage difference between said control voltage and a voltage on said control terminal, wherein said voltage on said control terminal changes in response to said reference current;
measuring a time period between a point in time when the reference current is activated and a point in time when the voltage difference increases to a threshold.
8. The method of claim 7 wherein said time period is used to determine said the displacement of the actuator.
9. The method of claim 7 wherein said time period is used to generate a plurality of voltages and corresponding actuator displacements.
10. The method of claim 7 wherein said time period is used to determine lens displacements in a digital camera.
11. The method of claim 7 wherein said time period is used to determine lens displacements in a digital camera while the camera is in use.
12. The method of claim 7 further comprising setting the control voltage from a controller and receiving timing information from the timer in said controller.
13. The method of claim 12 further comprising storing calibration factors in a memory coupled to said controller, wherein said controller retrieves calibration factors from said memory to determine said actuator displacement.
14. The method of claim 7 wherein said measuring a time period is performed by a counter.
15. The method of claim 7 wherein said comparing occurs after a settling period associated with said decoupling.
16. The method of claim 7 wherein providing a control voltage includes receiving a digital signal representing a voltage to be applied to said actuator, and converting the digital signal to an analog voltage.
17. An apparatus comprising:
an actuator having a control terminal configured to receive a control voltage to set a displacement of the actuator;
means for selectively decoupling said control voltage from said control terminal;
a reference current coupled to said control terminal when the control terminal is decoupled from said control voltage, wherein a voltage on said control terminal changes in response to said reference current;
means for comparing a voltage difference between said control voltage and the voltage on said control terminal;
means for measuring a time period between a point in time when the voltage on the control terminal changes in response to the reference current to a threshold.
18. The apparatus of claim 17 wherein actuator is a lens actuator and the control voltage sets a displacement of a lens.
19. The apparatus of claim 18 wherein the lens actuator is a MEMS device.
20. The apparatus of claim 17 wherein the capacitance on the control terminal is measured to adjust the control voltage.