This article presents a second-order noise-shaping (NS) successive approximation register (SAR) analog-to-digital converter (ADC) with a process, voltage, and temperature (PVT)-robust closed-loop dynamic amplifier. The proposed closed-loop dynamic amplifier combines the merits of closed-loop architecture and dynamic operation, realizing robustness, high accuracy, and high energy-efficiency simultaneously. It is embedded in the loop filter of an NS SAR design, enabling the first fully dynamic NS-SAR ADC that realizes sharp noise transfer function (NTF) while not requiring any gain calibration. Fabricated in 40-nm CMOS technology, the prototype ADC achieves an SNDR of 83.8 dB over a bandwidth of 625 kHz while consuming only 107 μW. It results in an SNDR-based Schreier figure-of-merit (FoM) of 181.5 dB.