A capacitance deviation-to-time interval
converter is presented for interfacing capacitive sensors.
It consists of two ramp integrators, two current-tunable
Schmitt triggers, and two logic gates. A prototype circuit
built using discrete components exhibits a resolution as
high as 13 bits and a linearity error less than ±0.2 %
when the output pulse is counted by a 20 MHz clock
signal. Its application to a humidity sensor is also
presented.