Integrated Hybrid Sub-Aperture Beamforming and Time-Division Multiplexing for Massive Readout in Ultrasound Imaging

This paper demonstrates hybrid sub-aperture beamforming (SAB) with time-division multiplexing (TDM) for massive interconnect reduction in ultrasound imaging systems. A single-chip front-end system prototype has been fabricated in 180-nm HV BCD technology that combines 5×1 SAB with 8×1 TDM to efficiently reduce the number of receive signal interconnect by a factor of 40. The system includes on-chip high voltage (HV) pulsers capable of generating unipolar pulses up to 70 V in transmit (TX) mode. The receiver (RX) chain consists of a T/R switch, a variable-gain low-noise amplifier (VG-LNA) with 4-step gain control (15-32 dB) for time-gain compensation followed by a programmable switched-capacitor analog delay-and-sum beamformer. The proof-of-concept prototype operates at 200-MHz clock frequency and the SAB provides 32-step fine delays with a maximum delay of 310 ns corresponding to better than λ/20 delay quantization at 5 MHz. With these specifications the SAB is capable of beam steering from 0° to 45° for a 5-element subarray with 150-micron pitch (λ/2), providing a near ideal phased array imaging performance. The sub-aperture beamformer is followed by the TDM system where each of the 8 channels is sampled at a rate of 25 MS/s after an antialiasing bandpass filter. Full functionality of the prototype chip is validated through electrical and acoustic measurements on a 1-D capacitive micromachined ultrasonic transducer (CMUT) array designed for intracardiac echocardiography (ICE).