A 9.84–73.2 nJ, 0.048 mm2 time-domain impedance sensor that provides values of resistance and capacitance

A new time-domain impedance sensor readout circuit based on 0.18-μm CMOS technology is presented. A current DAC is used to charge the device under test (DUT) to increase the node voltage of the DUT. Using a time-domain comparator and a counter, a time period between the start of charge till the moment that the node voltage reaches a reference level is recorded and digitally converted. The resistance and capacitance components of the impedance can be quantized by using the time period data. The fabricated prototype consumes only 9.84 to 73.2 nJ of energy and requires merely 3 ms per measurement, where both are >103 times' reductions as compared to the state-of-the-arts. Moreover, to the best of the authors' knowledge, this proposed readout chip is the first of its kind that is able to deduce each resistance and capacitance component of the impedance. The chip takes up 0.048-mm2 of area.