A High-Voltage Differential SPDT T/R Switch for Ultrasound Systems

An improved bootstrapped circuit topology is proposed for the design of a high-voltage, differential, single-pole double-throw transmit/receive switch for an ultrasound hand gesture recognition system. The differential transmit/receive switch is designed in a $0.18~\mu $ m HV BCD technology. It is intended to interface with bimorph piezoelectric micromachined ultrasonic transducer electrodes, although a single-ended version can also interface with conventional ultrasound transducers. A comprehensive analysis has produced useful insights, namely the dependence of off-isolation on high-voltage input slew rate, and the dependence of common-mode rejection ratio on threshold mismatch and timing misalignment. In addition, an extended model has been developed to predict harmonic distortion through a DMOS transistor. Measured results verify the effectiveness of the design guidelines and switch operation. The switch circuit exhibits $67~\Omega $ on-resistance and -63 dB off-isolation while occupying a modest area of $289~\mu $ m $\times 295~\mu $ m. The switch achieved a figure-of-merit with 74% improvement over the state-of-the-art. To the best of the authors’ knowledge, this differential switch is the first of its kind reported for piezoelectric micromachined ultrasonic transducer biomedical ultrasound systems.