Capacitive position sensing for capacitive drive MEMS devices
An apparatus for driving and position sensing in a comb-drive actuator includes a generator, a driver circuit, sensing circuitry, and signal processing circuitry. The generator is configured to apply a sensing-voltage to a first electrode of the comb-drive actuator. The driver circuit is configured to apply a drive-voltage to a second electrode of the comb-drive actuator, having an opposite polarity relative to the first electrode. The sensing circuitry is configured to measure at the second electrode a sensed-waveform resulting from the sensing-voltage applied to the first electrode. The signal processing circuitry is configured to estimate a position of the first electrode relative to the second electrode based on the sensed-waveform.
1. An apparatus for driving and position sensing in a comb-drive actuator, the apparatus comprising:
a generator, configured to apply a sensing-voltage to a first electrode of the comb-drive actuator;
a driver circuit, configured to apply a drive-voltage to a second electrode of the comb-drive actuator, having an opposite polarity relative to the first electrode;
sensing circuitry, which is configured to measure at the second electrode a sensed-waveform resulting from the sensing-voltage applied to the first electrode; and
signal processing circuitry, which is configured to estimate a position of the first electrode relative to the second electrode based on the sensed-waveform.
2. The apparatus according to claim 1 , wherein the sensed-waveform falls on a resistor connected in series to the second electrode.
3. The apparatus according to claim 1 , wherein the sensed-waveform is measured by a circuit having an adaptive reference ground.
4. The apparatus according to claim 1 , wherein the sensing-voltage comprises a sine waveform.
5. The apparatus according to claim 1 , wherein:
the generator is configured to apply the sensing-voltage to a common first electrode of two or more comb-drive actuators;
the driver circuit comprises two or more driver circuits configured to apply respective drive-voltages to two or more respective second electrodes of the two or more comb-drive actuators;
the sensing circuitry is configured to measure at the second electrodes respective sensed-waveforms resulting from the sensing-voltage applied to the common first electrode; and
the signal processing circuitry is configured to estimate positions of the first electrodes relative to the respective second electrodes based on the respective sensed-waveforms.
6. A method for driving and position sensing in a comb-drive actuator, the method comprising:
applying a sensing-voltage to a first electrode of the comb-drive actuator;
applying a drive-voltage to a second electrode of the comb-drive actuator, having an opposite polarity relative to the first electrode;
measuring at the second electrode a sensed-waveform resulting from the sensing-voltage applied to the first electrode; and
estimating a position of the first electrode relative to the second electrode based on the sensed-waveform.
7. The method according to claim 6 , wherein measuring the sensed-waveform comprises measuring the sensed-waveform that falls on a resistor connected in series to the second electrode.
8. The method according to claim 6 , wherein measuring the sensed-waveform comprises measuring the sensed-waveform using a circuit having an adaptive reference ground.
9. The method according to claim 6 , wherein applying the sensing-voltage comprises applying a sine waveform.
10. The method according to claim 6 , wherein:
applying the sensing-voltage comprises applying the sensing-voltage to a common first electrode of two or more comb-drive actuators;
applying the drive-voltage comprises applying respective drive-voltages to two or more second electrodes of two or more respective comb-drive actuators;
measuring at the two or more second electrodes respective sensed-waveforms resulting from the sensing-voltage applied to the common first electrode; and
estimating positions of the first electrodes relative to the respective second electrodes based on the sensed-waveforms.