Heterodyning technique to improve performance of delta-sigma-based beamformers

Delta-sigma (/spl Delta//spl Sigma/) modulators can implement a simpler digital ultrasound beamformer than can traditional architectures based on multi-bit analog-to-digital converters (A/D). The signal-to-noise ratio (SNR) of the /spl Delta//spl Sigma/ modulators, however, suffers from limited oversampling ratios. To improve the SNR of each channel, a mixing signal heterodynes narrowband signals to lower frequencies where the baseband /spl Delta//spl Sigma/ modulator performs better. Noise figure analyses are presented that illustrate the effectiveness of this technique in improving noise performance. Also, spectral Doppler and color flow simulations are presented that realistically emulate a 32 channel oversampled beamformer and compare these results with traditional and ideal systems.