A front-end integrated circuit for a 2D capacitive micromachined ultrasound transducer (CMUT) array as a noninvasive neural stimulator

In this paper, we present a front-end integrated circuit (IC) for an ultrasound neurostimulation system, to be interfaced with a 16×16 2D CMUT array to realize an ultrasound field pattern (USFP) using quantized phases and amplitudes. The IC uses a pulse width modulation (PWM) technique with a three-level pulse to generate excitation signals having multi-level quantized amplitudes. For a programmable phase delay, each transmitter (TX) element has a voltage controlled delay cell (VCDL) controlled by a global delay-locked loop (DLL). A 6.75-V supply voltage is generated by an on-chip 2:1 step-down charge pump. The IC was fabricated in a 0.35-μm 13.5-V DDD process. The nonlinearity of the phase delay is characterized and shown not to significantly degrade the quality of the projected stimulation pattern. In addition, we validated the beamforming and steering capability of the IC with a 16-element 1D CMUT array operating at 6 MHz as part of our initial characterization efforts before integration with a 2D array.