Electronics design for high density CMUT array based ultrasound imaging system
Rashid, Muhammad Wasequr
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In catheter based ultrasound imaging applications, gathering real-time imaging data from a large number of transducer array elements is extremely challenging with the standard interconnect and transducer technology as there is a restriction on cable count due to the diameter of the catheter. Intracardiac Echocardiography (ICE) imaging systems require many cables connecting the transducer array elements at the tip of the catheter to the backend imaging systems. Reducing the number of cables using highly integrated front-end electronics, is essential for 3-D ICE imaging systems with 2-D imaging arrays. Cable reduction would also reduce the cost of the current 2-D imaging ICE catheters with 1-D imaging arrays and can enable to ICE imaging under MRI by reducing the RF induced heating of the catheters. Current approaches to cable reduction tend to rely on area and power-hungry circuits to function, making them unsuitable for use in catheters. This research explores the design of the CMOS receiver circuitry which implements a Time Division Multiplexing (TDM) scheme to address the receive cable restrictions of the catheter. This approach, implemented in the form of a direct digital demultiplexing technique, allows for a reduction in the number of analog signal processing stages required. Receive multiplexing alone is not enough to reduce the cable count since the same elements in the arrays are used as transmitters. Therefore, the CMOS circuitry should integrate transmit beamforming as well. For this purpose, this study also explores an on-chip programmable transmit beamformer circuit for producing focused and steered transmit beams. In this thesis, a system which uses an e cient real-time programmable on-chip transmit beamformer circuitry to reduce the cable count on the transmit side and analog 8:1 Time Division Multiplexing with Direct Digital Demodulation to reduce the cable count on the receive side is described and initial imaging results are presented.