A fully integrated self-calibrating transmitter/receive IC for an ultrasound presence detector microsystem

A fully integrated transmitter/receiver ASIC for an ultrasound presence detection microsystem is described. The transducers consist of thermally excited silicon membranes which are fabricated using a standard silicon circuit technology plus one additional etching step. The mixed-signal chip is realized with no external components. It can be configured as either the transmitter or the receiver of the microsystem. As a transmitter, the silicon transducer is used as an electromechanical resonator to emit ultrasound at 80 kHz. In receive mode, the sensor sensitivity is automatically maximized by a self-calibrating scheme which tunes the receiver membrane resonant frequency to that of the transmitter.