A 4x Time-Domain Interpolation 6-bit 3.4 GS/s 12.6 mW Flash ADC in 65 nm CMOS

Abstract

A 6-bit 3.4 GS/s flash ADC in a 65 ㎚ CMOS process is reported along with the proposed 4x time-domain interpolation technique which allows the reduction of the number of comparators from the conventional 2 N -1 to 2 N-2 in a N-bit flash ADC. The proposed scheme effectively achieves a 4x interpolation factor with simple SR-latches without extra clocking and calibration hardware overhead in the interpolated stage where only offset between the 2 N-2 comparators needs to be calibrated. The offset in SR-latches is within ±0.5 LSB in the reported ADC under a wide range of process, voltage supply, and temperature (PVT). The design considerations of the proposed technique are detailed in this paper. The prototype achieves 3.4 GS/s with 5.4-bit ENOB at Nyquist and consumes 12.6 ㎽ power at 1 V supply, yielding a Walden FoM of 89 fJ/conversion-step.