We present a single-channel 10-b 400-MS/s successive approximation register (SAR) analog-to-digital converter (ADC) embodying a proposed 2-b/step conversion scheme with single reference voltage for the IEEE 802.11ac. By means of the said scheme, the proposed ADC requires only three capacitor arrays instead of at least four capacitor arrays in other capacitor digital-to-analog converter-based 2-b/step SAR ADCs. The proposed ADC features a small input capacitance loading, thereby alleviating the driving requirement of the power-hungry input buffer in the IEEE 802.11ac system; and features a symmetrical architecture with highly matched interconnections. In addition, the proposed ADC embodies a proposed high-speed dynamic comparator with kickback noise cancelation and high-speed successive approximation (SA) control logic for high conversion rate and resolution. The proposed ADC prototype fabricated in 65-nm CMOS process achieves signal-to-noise-and-distortion-ratio >52 dB across 200-MHz Nyquist bandwidth, while dissipating 5.61-mW power. The ADC prototype, when benchmarked with state-of-the-art 2-b/step SAR ADCs, features a highly competitive figure-of-merit, i.e., 43 fJ/conv.step.