Custom integrated circuit design for ultrasonic therapeutic CMUT array

This paper presents the design of a highly flexible and programmable transmit beam-former ASIC using a high voltage (HV) 0.35 mu m CMOS technology to be flip-chip bonded to a 4 x 4 CMUT array for ultrasound therapeutic applications. However, proposed IC can be used as a transmitter circuitry in color Doppler 3D imaging applications. In our proposed chip, each CMUT element is provided by an 8-bit shift register, an 8-bit comparator, a one-shot circuit with adjustable pulse width, a programmable pulse train generator and a HV pulser circuit. The interface electronics can generate two types of outputs with programmable focusing delays to 16 ultrasound transducer elements in different modes: The first mode is for generating single pulses in which the one-shot circuits adjust the width of the pulses from a few nanoseconds to 650 ns with enough resolution for different operating frequencies of ultrasound transducer. The second one has been considered for generating controllable pulse trains with output frequencies in the range of 1-10 MHz. At final stage the amplitudes of single pulses or pulse trains are increased up to 45 V using HV pulsers. Using an external control system like FPGA, the pulser circuit fires correspondent CMUT element when its stored shift register value is identical with the value of global counter