24.5 A 72GS/s 9b Time-Interleaved Pipeline-SAR ADC Achieving 55.3/49.3dB SFDR at 20GHz/Nyquist Inputs in 16nm FinFET

The ever-increasing demands of communication traffic have driven optical modules to scale beyond 100Gb/s. This evolves aggressive bandwidth and SNDR frontiers for their ADCs in the receiver to cope with advanced modulations and oversampling rates. Time-interleaving (TI) is indispensable for such the near-hundred GS/s envelope, but a massive TI factor confines the achievable SFDR as well as ENOB at wideband inputs over 20GHz [1]. The constraint primarily stems from two regimes, which are the bandwidth mismatch and implicit distortion in the interleaver. Relying solely on timing skew calibration [1]–[3] for skew-associated impairments is not sufficient since it only provides first-order correction for bandwidth mismatch. An additional order of amendment can be achieved by tuning the sampling capacitors [1], but the error detection mechanism remains unsound. Furthermore, the input buffers of the ADC, interfacing with high-frequency signals and short track time, give rise to distortions and gain attenuation, considerably ruining ADC performance. Minimizing the TI factor for a given sampling rate inherits a better interleaver performance by mitigating the mismatch and distortion sources. The unit-ADC composites SAR with pipeline can push the single-channel to 1GS/s+ [3], which in turn requires additional background inter-stage gain (ISG) calibration compared to its pure SAR counterparts. This work presents a 72GS/s time-interleaved pipeline-assisted SAR ADC, which leverages linearized wideband input buffers and a dual-path bootstrapped switch (BS) to facilitate >55dB SFDR for a 20GHz input. Furthermore, an R/R-based open-loop amplifier is introduced, omitting the ISG calibration in the 1.125GS/s unit pipeline-SAR ADC. The prototype achieves 46.4dB SNDR and 63.6dB SFDR at low input frequencies and 37.0dB SNDR and 49.3dB SFDR at Nyquist input. Fabricated in a 16nm FinFET technology, it consumes 393.6mW of power, yielding a 53.7fJ/conv.-step $\text{FoM}_{\mathrm{s}}$ with a 20GHz input.