UBC Theses and Dissertations
On the design of high-voltage analog front-end circuits for capacitive micromachined ultrasonic transducers (CMUT) Behnamfar, Parisa
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.
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