A sigma-delta-based sparse synthetic aperture beamformer for real-time 3-D ultrasound

Sigma-delta (/spl Sigma//spl Delta/) modulation allows delay resolution in ultrasound beamformers to be achieved by simple clock cycle delays applied to the undecimated bitstream, greatly reducing the complexity of the signal processing and the number of bits in the datapath. The simplifications offered by this technique have the potential for low power and portable operation in advanced systems such as 3-D and color Doppler imagers. In this paper, an architecture for a portable, real-time, 3-D sparse synthetic aperture ultrasound beamformer based on /spl Sigma//spl Delta/ modulation is presented, and its simulated performance is analyzed. Specifically, with a 65-element linear phased array and three transmit events, this architecture is shown to achieve a 1.1/spl deg/ beamwidth, a -54-dB secondary lobe level, and a theoretical frame rate of 1700 frames/s at /spl lambda//64 delay resolution using a second-order low pass /spl Sigma//spl Delta/ modulator. Finally, a technique for modifying the proposed multi-beam architecture to allow improved analog-to-digital (A/D) resolution by premodulating the input signal for bandpass /spl Sigma//spl Delta/ modulation is also presented.