An 11.0 bit ENOB, 9.8 fJ/conv.-step noise-shaping SAR ADC calibrated by least squares estimation

A noise-shaping SAR ADC implemented in 28 nm UTBB FDSOI is presented. A cascaded FIR-IIR loop filter topology is used, and implemented as an inverter-based switched-capacitor circuit. The loop filter also employs input buffers. To correct CDAC mismatch, an off-line calibration technique that estimates the CDAC calibration coefficients from a digitized test sequence is proposed and used. At 28 MS/s and Nyquist bandwidth of 1.75 MHz, the measured accuracy is 11.0 bit ENOB, and the Walden FOM 9.8 fJ/conv.-step.