Catheter-Mounted CMOS Front-Ends for Broadband Intravascular Ultrasonic Imaging.

Abstract

Intravascular ultrasonic (IVUS) imaging catheters currently use ceramic piezoelectric transducers to form radial images of blood vessel walls. Further improvements in image quality may be enabled through Capacitive and Piezoelectric Micromachined Ultrasonic Transducers (CMUTs and PMUTs). Polymer PMUTs offer many benefits in imaging quality, however, the low acoustic sensitivity and high electrical impedance of polymer PMUTs prevents unbuffered use with 50-Ω IVUS cables. Here, we present the design and optimization of an integrated CMOS front-end specifically designed to be integrated on a 0.8-mm imaging catheter. A series-duplexer topology with active limiter was selected for simplicity of integration, and compatibility with conventional high-voltage IVUS pulser-receiver systems. Noise optimization of the front-end revealed that an impedance-matching optimum exists, which balances the system parasitic capacitances relative to the transducer complex impedance. Optimized design equations compared favorably to simulation results in predicting front-end bandwidth and transducer-referred SNR. Large-signal transient simulation showed that the front-end can withstand 100-V pulses while recovering in 240 ns for echo reception. The integrated front-end occupied 0.74 × 1.8 mm die area (including large solder-bump bond pads), with an estimated transducer-referred noise floor of 6.5 over a 100-MHz imaging bandwidth.