This paper presents a SAR-assisted Continuous-time Delta-Sigma (CT Δ Σ ) ADC, which combines the energy efficiency of SAR ADCs with the relaxed driving requirements of CT Δ Σ ADCs, as well as similar anti-alias filtering. When clocked at 2.4GHz, the ADC achieves 77.5dB SNDR in 40MHz BW. It consumes 3.2mW, resulting in a state-of-the-art Walden FoM of 6.5fJ/cs and a Schreier FOM of 178.5dB.