A common plate is formed in a moveable element of a device, the device having an actuator coupled to drive the moveable element. A first plate and the common plate together form a first capacitance, while a second plate and the common plate together form a second capacitance, both of which varies as a function of displacement of the moveable element. A measurement circuit has an input coupled to the first plate, while an excitation voltage source has an output coupled to the second plate. A guard voltage source has an output coupled to a conductive portion of the device. Other embodiments are also described and claimed.