A 4MS/s 10b SAR ADC with integrated Class-A buffers in 65nm CMOS with near rail-to-rail input using a single 1.2V supply

We present a 10b differential SAR ADC integrated with unity gain (Class-A) voltage buffers, operating from a single supply voltage 1.2V and handling near rail-to-rail inputs. The two differential inputs are first compared and depending on the comparison result, the inputs are either swapped or not, after which these signals are buffered, sampled and converted. This way each of the two buffers needs to handle only half of the full-scale range which enables operation of the Class-A buffers at the ADC supply voltage while providing an overall near rail-to-rail (full-scale) input range for conversion. The buffered ADC can handle 2V
_P-P
differential input and consumes 149μW at 4MS/s to achieve a state-of-the-art Walden FoM of 87fJ/conversion-step including buffers. The buffered ADC was designed in a 65nm CMOS process and occupies an active area of 0.04mm
²
.