Capacitance-Controlled Oscillator with Enhanced Tuning Range using Negative Capacitance for Time-Based Sensor Interfaces

Since time-based sensor-to-digital conversion is gaining popularity in recent years, techniques to convert the sensor signal to a time-based signal are needed. Integration of a capacitive sensor in a capacitance-controlled oscillator (CCO) is one technique, but it suffers from sensor sensitivity degradation. To increase the sensitivity of the variation of the period of the CCO to the sensor variation, this paper proposes a technique which is based on cancelling part of the nominal capacitance C0 of the sensor with a negative capacitance. To demonstrate the concept, the Signal-to-Noise Ratio is shown to increase with over 25% for a coupled sawtooth CCO, as is validated by simulations in UMC130 CMOS technology.