A Bidirectional Readout Integrated Circuit (ROIC) with Capacitance-to-Time Conversion Operation for High Performance Capacitive MEMS Accelerometers

In this paper, a bidirectional readout integrated circuit (ROIC) with capacitance-to-time conversion operation has been proposed and demonstrated for high performance capacitive micro-electro-mechanical system (MEMS) accelerometers, which is implemented by a 0.35-mum CMOS EEPROM process. For the desired performance of the proposed ROIC, a bidirectional time-to-digital conversion (TDC) method with a capacitance-to-time (C-T) conversion operation is employed for the detection of the directions. At the condition of the reference capacitance (C
_Ref.
) of 20 pF, the new ROIC shows the positive sign-bit ('1') for the case of the sensor capacitance (C
_Sen.
) < 20 pF and the negative sign-bit ('0') for the case of C
_Sen.
> 20 pF, which lead to the bidirectional accelerometer operation. Consequently, the new proposed ROIC exhibits the bidirectional readout operation by the bidirectional TDC operation with the C-T conversion.