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 A-E 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.