Ultrasound beamformer using pipeline-operated S/H delay stages and charge-mode summation

The proposed ultrasound beamformer is based on the delay-and-sum beamforming principle. The circuit consists of several programmable delay lines. Each delay line is constructed by pipeline-operated sample-and-hold (S/H) stages with digitally-assisted delay control, which ensure delay-independent gain and good timing accuracy. The summation is realised in the charge domain using the charge-averaging method, which consumes virtually no extra die area or power. A prototype beamformer has been fabricated in a 0.35 µm CMOS process to interface nine transducer elements. Measurement results show that this circuit consumes much less power and chip area than the prior art, while maintaining good accuracy and flexibility.