This article presents a compact 13-bit 200-MS/s pipelined successive-approximation register (SAR) analog-to-digital converter (ADC) with a robust current-biased ring amplifier (ring-amp) and kT/C noise cancellation. The proposed current-biasing scheme using split capacitors significantly enhances the PVT robustness of the ring-amp. With additional split capacitors used for current-biasing, the kT/C noise cancellation technique can be seamlessly implemented in this architecture. With kT/C noise cancellation, the input-referred thermal noise can break the input sampling kT/C noise limit. As a result, the input sampling capacitance can be greatly reduced. With only 128-fF single-end input sampling capacitance, the prototype ADC implemented in a 28-nm process achieves 67-dB SNDR with only 0.004-mm2 core area. The power consumption at 200 MS/s is 1.3 mW, yielding a Schreier figure of merit of 175.5 dB and a Walden figure of merit of 3.7 fJ/conversion-step.