Target voltage independent capacitance measurement circuit implemented by 0.18 µm CMOS for PWM-MEMS control

This paper proposes a target voltage independent capacitance measurement circuit aiming for PWM-MEMS control. PWM-MEMS, which is controlled by time domain PWM signal, instead of voltage domain analog signal, is emerging for fast-response MEMS control. Real-time angle measurement for feedback control is essential for the PWM-MEMS. Capacitance measurement is one of promising technique for the angle measurement without any additional optical components. To realize real-time capacitance measurement for PWM-MEMS with minimal disturbance to MEMS operation, measurement at driving electrode is expected, and short measurement time within off state of PWM signal, small amount of charges for measurement are required. We have designed and fabricated the proposed capacitance measurement circuits in 0.18μm CMOS, and measurement result shows that measurement time of 60μs, charge requirement of 80fC with capacitance measurement at target voltage range of 2.5V - 1.5V.