A 9.7fJ/Conv.-Step Capacitive Sensor Readout Circuit with Incremental Zoomed Time Domain Quantization

This paper presents a capacitive sensor readout circuit with an incremental zoom current-controlled oscillator (CCO)-based timedomain (TD) ΔΣM. It supports single-sensor measurement, leading to 2x savings in sensing hardware compared to dual-sensor schemes. A low-cost 5b TD-ΔΣM is implemented with a 7- stage ring-CCO and a double-PFD (DPFD) quantizer. To further boost its speed, a fast start-up scheme is designed for the CCO quantizer. Combining all these merits, the proposed readout circuit achieves 0.23fF resolution while dissipating only 61pJ per conversion with a short measurement time of 4.1μs. To the authors’ best knowledge, it realizes the best energy efficiency and shortest measurement time among all high-resolution capacitanceto-digital converters (CDCs) achieving over 12 ENOB.