A 12-b 1-GS/s 31.5-mW Time-Interleaved SAR ADC With Analog HPF-Assisted Skew Calibration and Randomly Sampling Reference ADC

This paper presents a 12-b, 1-GS/s ADC array, realized by time-interleaving four 250-MS/s pipelined SAR ADCs, with integrated on-chip reference voltage buffers. A reference ADC-based calibration algorithm treats static nonlinearity, gain, and offset errors in the array. Timing-skew errors between the sub-ADCs are distinguished from those of the gain mismatches by the assistance of an analog high-pass filter (HPF) for input slope information and subsequently corrected by digitally controlled delay lines (DCDLs). Directly driven off the on-chip 50-Ω termination resistors without any dedicated input buffer, the 65-nm CMOS prototype ADC array also employs a frequency-hopped, randomly-sampling scheme for the ref. ADC, eliminating the spectral effect of its interference to the main array. The core ADC consumes 31.5 mW and occupies an area of 0.27 mm ² , including nine on-chip reference voltage buffers, the ref. ADC, and the HPF path. The measured peak signal to noise and distortion ratio of the array is 65.3 dB, and the measured spurious-free dynamic range is >70 dB from dc to 500 MHz at 1 GS/s with calibration. The prototype ADC chip achieves an figure of merit of 20.9 and 59.7 fJ/step (the latter is limited by the jitter of an off-chip clock source) for a low-frequency input and a Nyquist input, respectively.