Supply-Doubled Pulse-Shaping High Voltage Pulser for CMUT Arrays

A supply-doubled pulse-shaping high voltage (HV) pulser is presented for medical ultrasound imaging applications, particularly those that use capacitive micromachined ultrasonic transducers (CMUTs). The pulser employs a bootstrap circuit combined with dynamically biased stacked transistors, which allow HV operation above process limit without lowering device reliability. The new pulser overcomes supply voltage limitation of conventional unipolar pulsers by generating output signals that are almost twice the supply level. It also can generate three-level pulses to further optimize the transmit pressure signals. A proof-of-concept prototype has been implemented in 0.18-μm HV CMOS/DMOS technology with 60 V devices. Measurement results show that the HV pulser can safely generate controllable three-level pulses with up to 85 V
_pp
from 45 V supply. Acoustic measurements are conducted connecting the pulser to a CMUT with 2 pF capacitance and 8.3 MHz center frequency. The pulse shape has been adjusted for the CMUT under test to generate maximum pressure output and the results are in good agreement with a large signal CMUT model.