High Resolution ADC for Ultrasound Color Doppler Imaging Based On MASH Sigma-Delta Modulator

A high precision quantization ultrasound imaging system, capable of capturing small variances of the echo signal with a wide dynamic range, is important for producing accurate diagnostic outputs. Commercial ultrasound systems, typically utilizing 12 or 14 bits analog-to-digital converters (ADCs), lack the ability to measure blood flow deep inside the tissue and may be affected by surrounding tissue noise.

In this study, we propose a newly designed ADC with over 20-bit resolution. The superior performance was achieved by shaping the quantization noise with a [Formula: see text] sigma-delta modulator (SDM), and filtering the shaped noise at high frequencies by a digital decimation filter.

Designed in a mature 0.35 μm CMOS technology and powered by a 3.3 V voltage supply, the proposed SDM integrated circuits (IC) model achieved a signal to noise and distortion ratio (SNDR) of 109.5 dB, and an effective number of bits (ENOB) of 17.9-bit in an 8 MHz bandwidth. Eight identical SDMs were integrated onto one chip, and the entire layout occupied an area of 4.8 mm × 5 mm. A total of sixteen 8-channel SDM IC models were connected to all elements of the array transducer.

Simulated performance with blood flow evaluation datasets using 12-bit and 20-bit ADCs demonstrates that the proposed 20-bit ADC provides superior overall performance on image contrast and estimation accuracy of the blood speed.

Owing to these advantages, the 20-bit ADC shows promise for future development of ultrasound imaging systems, especially for color Doppler imaging.