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 3D-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 inverterbased 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 0.18μm CMOS process, the ultrasound AFE occupies a low silicon area of 0.052 mm2/channel, achieves 74.93 dB dynamic range (DR), 10.9nV/√Hz input referred noise, and -58.33 dB total harmonic distortion (THD). The average power consumption is 1.34mW/channel.