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On the design of high-voltage analog front-end circuits for capacitive micromachined ultrasonic transducers (CMUT)

University of British Columbia

In ultrasound imaging, capacitive micromachined ultrasonic transducer (CMUT) technology has become a promising alternative to conventional piezoelectric- based technology. This work focuses on various aspects of CMUT-based imaging technologies. In the context of CMUT design and integration with associated electronics, flexible and reliable CMUT models that can be seamlessly simulated with the read-out circuits and provide insights in the system-level performance are of great importance. This work proposes a generic Verilog-AMS model for CMUT sensors that takes into account the non-linearities, dynamic behavior and harmonic resonances of the CMUT. This model is able to provide reliable estimations of the pull-in voltage as well as the resonance frequency and the spring softening effect. To improve the signal-to-noise ratio (SNR), integrating the CMUT transducer with the front-end electronics is critical. Design and implementation of a comprehensive analog front-end system in a 0.8μm high-voltage CMOS technology which includes high-voltage and fast-switching transmitters as well as low-power variable-gain receivers is presented. Co-simulation of the front-end electronics and the CMUT model demonstrates full system functionality. Experimental results of the system at the transmit mode confirm the reliability of this co-simulation. An on-chip adaptive biasing unit (ABU) is also included in the design which aims to improve the CMUT receive sensitivity. The ABU consists of a DC-DC converter to generate a range of bias voltage levels and a digital control unit to select the desired voltage. Co- simulation of the ABU with the Verilog-AMS model confirms the increase in the CMUT sensitivity in receive mode. In the context of CMUT super-resolution imaging, we present the design of a transceiver circuit in a 0.35μm high-voltage CMOS technology that supports both the fundamental and asymmetric modes of operation. The transmitter provides high- voltage pulses to the CMUT electrodes. The receiver includes transimpedance analog adders to add the fundamental mode in-phase signals as well as differential amplifiers to combine the out-of-phase signals of the asymmetric modes. Furthermore, low- power variable-gain stages are included to amplify the resulting signals and facilitate interfacing to the ultrasound imaging machine for additional processing and display. The design functionality is confirmed by experimental results.

Text

2014-09-29

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/50469

Electrical and Computer Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/