Electronic interface design for an electrically floating micro-disc

The design of an electronic interface for an electrically floating micro-disc is
presented. The system, based on a second order electromechanical –
modulator, can be used as a multi-axis capacitive accelerometer with the
proof mass levitated by electrostatic forces. A synchronous detection
scheme, used to sense the position of the proof mass, has been designed,
simulated in PSpice
TM
and successfully implemented on a PCB. The
interface contains a differential pick-off with no ohmic connection to the
proof mass, which distinguishes the circuit from typical sensing circuits for
MEMS capacitive accelerometers. A noise analysis of the pick-off circuit
was performed, and an electronic equivalent model of the sensing circuit has
been developed and used to analyse the linearity of its transfer function. The
linearity of the sensing circuit was confirmed experimentally using the PCB
implementation.