A PVT-Robust 8b 20GS/s Time-Interleaved SAR ADC with Quantization-Embedded Current-Mode Buffer and Differ-Based Dither Timing Skew Calibration

Wide bandwidth (BW) and moderate-resolution ADCs with a sampling rate exceeding 10GS/s play a vital role in wireline receivers. Time-interleaved (TI) SAR ADCs retain low power but with exacerbated input BW limitation in massive TI factor. Although such an obstacle can be alleviated by the hierarchical sampler [1], the remaining long routings [2] among the bulky TI channels jeopardize efficiency and linearity. Alternatively, the TI time-domain (TD) ADC [3] reduces the channel number achieving superior BW; it however desires much heavier calibration overhead than SAR ADCs. To tackle the routing constraints and simultaneously source TD-ADC's pluses, this paper develops a PVT-robust quantization-embedded current-mode (QE-CM) buffer, which facilitates a current-domain TI input signal distribution; it not only decouples the BW issue from extensive routings but also enables the MSBs' quantization in parallel with signal buffering from its inherent TD feature, speeding up the single-channel 8b SAR ADC to 1.25GS/s. The prototype also features a signal-independent background timing calibration based on [4], while incorporating the proposed differ-based dither injection to accelerate the convergence speed and accuracy. The 16× QE-CM-assisted TI SAR ADC achieves 38.93dB SNDR and 51.87dB SFDR with a Nyquist input at 20GS/s, facilitating a >20GHz ERBW. It experiences <1.0dB and <1.5dB SNDR variations from -40°C to 85°C and under ±5% supply variation, respectively.