Capacitance-controlled oscillator optimization for integrated capacitive sensors with time/frequency-based conversion

AbstractTechnology scaling improves timing resolution, but diminishes voltage resolution, so time-/frequency-to-digital conversion is gaining popularity. In traditional amplitude-based converters, the sensor signal typically has to be pre- processed (amplified, filtered, etc) before feeding it to the converter. In the context of time-based converters, the conversion of the sensor to a frequency/time signal can be seen as pre-processing, after which it is fed to the time-to- digital converter. This paper focuses on the optimized conversion of a capacitive sensor (MEMS) to a time/frequency signal by using a Capacitance-Controlled Oscillator (CCO). In this way the sensor is directly converted to a usable time signal, so other pre-processing such as amplification and filtering can be avoided. Different oscillator topologies are investigated, designed in UMC130 CMOS technology, and compared to each other, based on key parameters such as tuning range, linearity, phase noise and power consumption. It is indicated which oscillators are suited for which applications