A 12b 160MS/s synchronous two-step SAR ADC achieving 20.7fJ/step FoM with opportunistic digital background calibration

A 12b two-step pipelined SAR ADC reports a 66.7dB SNDR and an 86.9dB SFDR for a 5MHz sinusoidal input at 160MS/s. A digital background calibration based on opportunistic PN injection treats both DAC mismatch and residue-amplifier gain errors. The calibration enables a significant downsizing of the ADC input capacitance to yield a wideband, highly linear input network and an over-80dB SFDR while digitizing inputs from DC to 300MHz at full speed. The conversion FoM of this ADC is 20.7fJ/step at Nyquist. The prototype occupies an active area of 0.042mm² in a 40nm CMOS low-leakage digital process.