A capacitance-to-digits readout circuit for integrated humidity sensors for monitoring the in-package humidity of ultra-small medical implants

There remains a need for satisfactory integrated sensors that can monitor humidity inside small active implanted devices in which delicate electronics are operating. This paper describes a simple capacitance-to-digits readout circuit for a capacitive humidity sensor for ultra-small medical implants. The proposed readout circuit provides a larger dynamic range than conventional capacitance readout circuits by removing the parasitic capacitance from the measured capacitive input. The circuit was designed in XFAB's 0.6-μm CMOS technology and provides 1 % resolution in measuring relative humidity