A Calibration-free 80MHz CT DSM Using Dual Quantization and ISI Shuffler Achieving 106.2dB SFDR

Continuous-time (CT) Delta-Sigma-Modulators (DSMs) are favorable implementations of wide band receiver analog-to-digital converters (ADCs). Multi-bit (MB) quantization allows for higher resolution, improved jitter robustness, larger maximum stable amplitude (MSA), and reduced dynamic requirements within the loop-filter (LF). A key bottleneck for MB DSMs is digital-to-analog converter (DAC) linearity by mismatch, which typically requires mismatch shaping or calibration techniques [1]–[4]. As oversampling ratio (OSR) decreases, static mismatch shaping techniques become less effective [5], and required calibration circuitry results in increased area, power consumption, and long start-up calibration times [4]. Dynamic DAC errors also cause linearity degradation at high sampling frequencies [6], which is mitigated by the use of RTZ/RTO techniques [5] or calibration [2]. While 1 b or 1.5b DSM largely avoid the mismatch problem [7]–[9], they reduce the MSA and require a much higher OSR and sampling frequency. Dual quantization DSM offer an alternative solution [10]: they use a noise-shaping feedback DAC with low output bitwidth in a multibit DSM to inherit all benefits of a MB DSM but avoid the non-linear MB DAC. Previous work has limited the order of the digital DSM (DDSM) for stability and increased its OSR for sufficient resolution [10], disadvantageous for wide bandwidths. Multi-stage noise SHaping (MASH) DDSM have been introduced to achieve high resolution with low OSR, but they require recombination filters that are prone to mismatch [11]. This paper presents a wideband CT DSM that achieves high linearity without any calibration of static and dynamic DAC errors by employing a Sturdy MASH (SMASH) DDSM dual quantization DAC.