UC Berkeley

Ultrasound has long been used for medical imaging. Recent advances of miniaturized MEMS ultrasonic transducers new applications such as gesture recognition, personal fitness devices, and fingerprint sensors. These devices are considerably smaller than conventional transducers. To benefit from their lower excitation power requirements and address the reduced sensitivity requires the design of novel interface electronic circuits.

The first part of this thesis describes new circuits capable of generating all the high voltage drive signals for MEMS transducers on-chip from a single low-voltage supply. A novel level shifter design lowers power dissipation by suppressing the crow-bar current of conventional designs. The techniques have been verified in a seven channel ASIC and applied to a personal fitness application.

The second part of the thesis applies the new circuit ideas to the realization of an ultrasonic fingerprint sensor comprising over 6000 individual transducer elements in a 5x4 mm^2 area, each with drive and sense electronics. Unlike prevalent optical or capacitive fingerprint sensors, the ultrasonic solution is capable of recording both the surface and inner layers of the finger, resulting in reduced susceptibility to spoofing attacks.