An ultrasound beamforming method using 1.5-bit ADCs for portable ultrasound scanners

In this paper, a novel 1.5-bit beamforming algorithm and its architecture for ultra small ultrasound scanners is presented, in which the received RF signals are quantized into 3 levels, -1, 0, +1 and the 1.5-bit samples from all active elements are aggregated, taking into account dynamic focusing delays. It is obvious that the 1.5-bit quantizer is greatly simpler than conventional multi-bit ADCs. Since reducing one bit in quantization reduces the SQNR by 6 dB, however, the 1.5-bit beamforming method suffers from low SNR problems. To improve the SNR of the 1.5-bit beamformer, a high sampling rate and a simple dithering technique are used. We verified experimentally that the dithering technique can improve the SQNR by about 12 dB. The experimental results with in-vivo data show that a 64 channel 1.5-bit beamformer provides 7.5 MHz linear array images that might be acceptable for some point-of-care applications when the sample rate is 80 MHz.