A 1.25-GS/s 10-bit single-channel ring amplifier-based pipelined ADC in 28-nm CMOS

This paper proposed a pipelined analog-to-digital converter (ADC) that utilizes a high-linearity input buffer and a two-step input-split fully differential ring amplifier (ringamp). The implemented input buffer based on a gain-boost cascode current source, is optimized for linearity over a wider frequency range by suppressing fluctuations in tail current. To save power consumption without compromising common-mode and power-supply rejection, a fully differential ring amplifier is employed as the residue amplifier. Additionally, a correlation-based calibration is implemented, which involves injecting pseudo-random dither signals into each multiplying digital-to-analog converter (MDAC) stage to enhance linearity. Fabricated in a 28-nm CMOS process, the 1.25-GS/s 10-bit ADC achieves a spurious-free dynamic range (SFDR) of 70.7 dB and a signal-to-noise-and-distortion ratio (SNDR) of 50.3 dB at Nyquist input. The core conversion circuits of the ADC consume only 30.2 mW from a single 1-V supply. This translates to a Walden figure of merit (FoM) of 90 fJ/conversion-step and a Schreier FoM of 153.5 dB, respectively.