Integrated-circuit implementation of a matched-cell dynamic focusing architecture for a 5-channel, 50-MHz planar annular array

We have developed an integrated circuit for dynamically focusing a high-frequency (50 MHz) 5-channel planar annular array. The IC uses a 0.5 μm gate length CMOS process and measures 2 mm by 2 mm. High-impedance preamplifiers are included on each channel. The architecture is based on a collection of identical analog delay cells. Focusing of the array is accomplished by varying the delay of all cells simultaneously. Matched-cell architectures can be developed for linear arrays, linear phased arrays, and curved annular arrays, but the simplest architecture results for a planar annular array. Simulations of the one-way receive radiation pattern for a 1.7-mm diameter planar annular array using this architecture indicate a -6 dB beamwidth that increases smoothly from 93 μm to 220 μm over the axial range from 3.2 mm to 8.0 mm. The one-way beamwidth of a single-element transducer of the same diameter exceeds 1.4 mm over the same range. Dynamic focusing experiments have been performed using coaxial cables to simulate differential delays between channels from an axial ultrasound point source