Offset Correction in Dual-Chopper Read-Out Circuits for Half-Bridge Capacitive Accelerometers

Abstract:
Sensor read-out circuits using half-bridge capacitive accelerometers suffer from a signal offset due to production mismatches. This paper describes a two-part solution to reduce the offset within the circuit to a minimum. A capacitor array is used to apply a coarse signal correction by placing digitally controlled capacitors in parallel to the sensor capacitors. The second part consists of a current DAC placed within a differential amplifier to balance out unsymmetric currents caused by the signal offset. A binary search algorithm is applied to determine the optimal configuration of both parts. The offset correction method was implemented to a dual-chopper read-out circuit and reduces the sensor offset to under 0.04 %.