A 10.9-nV/√Hz, 74.9-dB DR, 20-MS/s Ultrasound Analog Front End for Fully Digital Beamforming

This letter presents a compact and energy-efficient analog front-end (AFE) circuit for fully digital beamforming in endoscopic and catheter-based 3-D ultrasound imaging. The AFE converts single-ended analog input from each transducer element into a 10-bit digital output through a low-noise amplifier (LNA) and a 20-MS/s SAR ADC. To minimize chip area and power consumption, the LNA employs a capacitor-splitting inverter-based amplifier with dynamic power control, while the ADC utilizes unit-length capacitors and digital error correction. A modified monotonic switching improves the conversion rate, and the kickback noise is reduced by an enhanced Elzakker comparator. Fabricated in a 0.18- $\mu $ m CMOS process, the ultrasound AFE occupies a low silicon area of 0.052 mm2/channel, achieves 74.93-dB dynamic range (DR), 10.9-nV/ $\surd $ Hz input referred noise, and −58.33-dB total harmonic distortion (THD). The average power consumption is 1.34 mW/channel.