A Low-Power 8-to-12-bit Reconfigurable SAR ADC for Portable Ultrasound Systems

A low-power reconfigurable successive approximation register (SAR) analog-to-digital converter (ADC) for portable ultrasound systems is presented. The ADC features a high power-efficiency 8-to-12-bit capacitive digital-to-analog converter (CDAC), and a "1-step" switching scheme is proposed to further reduce the switching energy of CDAC. A body-biasing technique is employed to calibrate the offset of the comparator. The ADC operates at 6.25 MS/s in 9-to-12-bit modes and can operate at 50 MS/s in the 8-bit mode. Designed in a 40-nm CMOS technology, the proposed reconfigurable SAR ADC achieves a post-simulated signal-to-noise and distortion ratio (SNDR) of 49.3/54.9/60.7/67.0/72.0 dB and a spurious-free dynamic range (SFDR) of 65.5/68.0/77.4/82.8/88.9 dB with a power consumption of 55.3/56.3/58.7/60.1/61.6 µW in 8/9/10/11/12-bit resolution modes at 6.25 MHz sampling rate, 49.0 dB SNDR and 65.3 dB SFDR with 332.5 µW power consumption in 8-bit resolution mode at 50 MHz sampling rate.