A 1 MHz BW 34.2 fJ/step Continuous Time Delta Sigma Modulator With an Integrated Mixer for Cardiac Ultrasound.

Fully digitized 2D ultrasound transducer arrays require one ADC per channel with a beamforming architecture consuming low power. We give design considerations for per-channel digitization and beamforming, and present the design and measurements of a continuous time delta-sigma modulator (CTDSM) for cardiac ultrasound applications. By integrating a mixer into the modulator frontend, the phase and frequency of the input signal can be shifted, thereby enabling both improved conversion efficiency and narrowband beamforming.

Analysis of the Distortion Mechanism in Delta-Sigma Beamforming.

Dynamic receive beamforming on a Delta-Sigma modulator's low-resolution output bit-stream suffers from a severely increased noise floor, rendering the promising method infeasible. This paper addresses the mechanism behind the increased noise floor. By using multirate theory and bifrequency analysis, we show that the increased noise floor is caused by aliasing/imaging of the powerful quantization noise from specific frequency regions according to the focus depth.