An 8-bit 10-GHz 8x time-interleaved successive-approximation-register (SAR) analog-to-digital converter (ADC) incorporates an aggressively scaled digital-to-analog converter (DAC) with grouped capacitors in a symmetrical structure to afford a threefold reduction in the bottom-plate parasitic capacitance. A detailed study rigorously analyzes the effect of gradient on the proposed DAC layout. The DAC additionally implements quantized sub-radix-2 scaling with redistributed redundancy. A high-speed dual-path bootstrapped switch decouples the critical signal from the nonlinear parasitic capacitance to boost the sampling spurious-free dynamic range by more than 5 dB. Fabricated in a 28-nm CMOS process, the ADC demonstrates an SNDR of 36.9 dB at Nyquist while consuming 21 mW, yielding a figure-of-merit of 37 fJ/conv.-step, the best among state-of-the-arts.