This paper presents an 8b 2.5-GS/s single-channel CDAC-assisted three-stage subranging ADC using reference-embedded comparators (RECs). In this work, both the power consumption and calibration overhead of the RECs are largely reduced by a simple capacitor DAC (CDAC) designed for this subranging ADC. In addition, the severe CDAC gain error is also largely reduced by a simple gain error compensation design, which is not only insensitive to the PVT variation but is also a low-complexity design. This ADC is implemented in 28-nm CMOS technology and occupies an active area of 0.024 mm². With a Nyquist-rate input at 2.5 GS/s, the measured SNDR is 44.8 dB with a 3.5-mW power consumption only. This ADC achieves a Walden Figure-of-Merits of 9.8 fJ/conv.-step only. Compared to the single-channel prior-art ADCs with a sampling rate ≥1.5 GS/s and a resolution of 6-10b, this work advances the state-of-the-art by nearly 2×.