Parasitic Capacitance Cancellation and SNR Improvement for Capacitance-to-Digital Converters based on a Switched-Capacitor Feedback

MEMS microphones for human-to-machine interface applications require small, low-power readout circuits. One approach to enhance scalability is to eliminate the microphone biasing circuit. The feasibility of this approach has been demonstrated by employing a switched-capacitor-based feedback to a voltage-controlled oscillator. The resulting capacitance-to-digital converter offers a wide input dynamic range, exceeding the microphone requirements. This manuscript proposes a further improvement: the oscillation frequency depends on the difference between a sensing and a reference capacitance. This approach provides two main advantages. Firstly, it compensates for the parasitic capacitance, which reduces conversion sensitivity. Secondly, it allows trading surplus dynamic range for an increase in signal-to-noise ratio at the same power consumption.