MEMS driver
Systems and methods provide actuator control. Actuator control is provided via charge control as opposed to voltage control. A driver for driving an actuator can include a charge pump for injecting charge into one or more capacitive elements of the actuator. The driver can further include a capacitance detection aspect for detecting the capacitance of the capacitive elements of the actuator to determine positioning of the actuator.
1. A driver device, comprising:
a charge pump to generate voltage required to inject charge into an actuator;
a charge sink through which the actuator can be discharged, wherein the charging and discharging of the actuator effectuates movement of the actuator; and
a switch for operatively connecting the charge pump and the charge sink to the actuator;
wherein stability of the actuator is increased by virtue of a charge control, wherein the actuator comprises a comb drive, wherein the comb drive is maintained in a stable position via an electrostatic force as a result of the charge control, a capacitance of the comb drive having an inverse relationship to the voltage, the electrostatic force adding to an electrostatic spring force associated with the comb drive, wherein an effective stiffness of the comb drive resulting from the added electrostatic force is approximately three times greater than an actual physical stiffness of the comb drive.
2. The driver device of claim 1 , wherein the driver device interfaces with a controller for controlling the movement of the actuator though one of a parallel digital interface or a serial peripheral interface.
3. The driver device of claim 2 , wherein the parallel digital interface is operative to transmit pulse width modulated signals to control the injection of charge into the actuator and the discharging of the actuator.
4. The driver device of claim 1 , wherein the charge pump is operatively connected to a charge capacitor for the charging of the actuator.
5. The driver device of claim 4 , wherein the charge sink is operatively connected to a discharge capacitor through which the actuator is discharged.
6. The driver device of claim 1 , wherein the charge pump and the charge sink are controlled by a precision current source and a precision current sink, respectively.
7. The driver device of claim 1 , wherein the actuator receives a varying voltage signal injected therein to determine a capacitance of the actuator.
8. The driver device of claim 7 , wherein the charging and the discharging of the actuator is performed sequentially at a frequency higher than a resonant frequency associated with the actuator to determine the capacitance of the actuator.
9. A driver device, comprising:
a driver circuit for driving a MEMS actuator via charge control to induce voltage that results in desired movement of the MEMS actuator while allowing the voltage to vary, the driver circuit, comprising:
a charge pump configured to inject charge into the MEMS actuator;
a charge sink configured to sink charge from the MEMS actuator; and
a switch configured to switch at least one of the charge pump and the charge sink to an appropriate capacitive element of the MEMS actuator;
wherein stability of the MEMS actuator is increased by virtue of the charge control, wherein the MEMS actuator comprises a comb drive, wherein the comb drive is maintained in a stable position via an electrostatic force as a result of the charge control, a capacitance of the comb drive having an inverse relationship to the voltage, the electrostatic force adding to an electrostatic spring force associated with the comb drive, wherein an effective stiffness of the comb drive resulting from the added electrostatic force is approximately three times greater than an actual physical stiffness of the comb drive.
10. The driver device of claim 9 , wherein an operational voltage limit of the MEMS actuator is increased by virtue of the charge control relative to a conventional voltage-controlled driver device.
11. A method, comprising:
successively charging and discharging an actuator to effectuate movement of the actuator;
determining a capacitance of the actuator to determine a position of the actuator resulting from the movement of the actuator by sensing voltage at an input of the actuator; and
measuring a slope of a voltage ramp up or ramp down resulting from the successive charging and discharging with a differentiator circuit and an analog to digital converter (ADC), the voltage ramp being a function of the capacitance of the actuator.
12. The method of claim 11 , further comprising adjusting charging and discharging periods to be longer or shorter relative to each other to allow for desired movement of the actuator.
13. The method of claim 11 , wherein a frequency of the charging and discharging is greater than a mechanical resonant frequency of the actuator to prevent inadvertent movement of the actuator.
14. The method of claim 11 , wherein the measuring of the voltage ramp comprises measuring a ramp up in output voltage.
15. The method of claim 14 , wherein the measuring of the voltage ramp further comprises measuring a peak voltage associated with the ramp up in output voltage.
16. The method of claim 11 , further comprising measuring the time between a change in output voltage reflected by the voltage ramp up and ramp down with a comparator.
17. The method of claim 11 , wherein the determining of the capacitance of the actuator further comprises sampling voltages induced by the successive charging and discharging of the actuator.
18. The method of claim 11 , wherein the determining of the capacitance of the actuator comprises generating a varying voltage resulting in the voltage at an input of the actuator and sensing coupling via a capacitor.