A 20MHz-BW 12.3-ENOB NS SAR ADC with a 3rd-order Multi-Input Filter and a PVT-Robust Ratio-Based FIA

Combining the noise-shaping (NS) technique with the SAR converter enables high resolution while maintaining state-of-the-art power efficiency and minimal area occupation [1]. However, the performance of existing NS SAR ADCs drops significantly for bandwidths higher than a few MHz, making the NS SAR unattractive for high-speed applications such as wireless communications. Single-core wideband solutions use passive residue processing [2]–[5] to implement noise shaping with minimal time and power overhead, but the resulting noise transfer function (NTF) is less sharp than that of active filters typically used in narrow-band designs, leading to resolutions around 11 ENOB. On the other hand, implementing a high-bandwidth active solution is challenging for two main reasons. First (1), increasing bandwidth requires working with a minimal OSR. Achieving good resolution at a low OSR demands sharp, high-order shaping with precise control of NTF poles and zeros, precluding the use of most open-loop amplifiers due to their sensitivity to PVT variations. Second (2), increasing the sampling frequency reduces the time available for residue processing. Consequently, it is necessary to expand the bandwidth of loop-filter amplifiers, which implies an increase in area, power consumption, and parasitic capacitance. This work addresses these issues by proposing (1) a dynamic open-loop floating inverter amplifier (FIA) with a ratio-based approach to control all loop-filter coefficients through component ratios and (2) a novel 3rd -order loop filter architecture that relaxes the amplifier by reducing its capacitive load, allowing faster operation.