Improved Sigma-Delta ultrasound beamformers with adaptive low-pass decimation filters

Sigma-Delta (Σ-Δ) beamformers have been proposed to reduce hardware complexity of the phased array front-end circuitry in digital ultrasound imaging systems. However, the sample repetitions involved in dynamic focusing degrades the image quality due to the elevated noise level. Thus, conventional low-pass decimators are deemed to be insufficient to suppress the elevated in-band noise floor. This paper shows that, adaptive rank-order filters in combination with the low-pass decimators following the beam summation are adequate to suppress the in-band noise components. As a result, we propose a novel hardware efficient digital beamformer employing single-bit Σ-Δ modulators incorporated with adaptive reconstruction filters. Simulations using experimental phantom data sets have shown that the proposed structure ensures high quality B-scan images comparable to the ones obtained by multi-bit A/D beamformers by preserving the hardware simplicity of the conventional single-bit Σ-Δ beamformers.