System-Level Mitigation of Undersampling ADC Nonlinearity for High-IF Radio Receivers

Over the last years ongoing advances in ADC technology have enabled RF signals to be sampled at IF frequencies. Undersampling is nowadays employed in software-defined radio or radar receivers and offers the possibility to relieve requirements in the analog receiver partition. Unfortunately, when moving to higher IF concepts, this becomes demanding for the ADC itself, because of inherent spurious-free dynamic range (SFDR) roll-off that increases with input frequency. This fact often limits the receiver's IF placement to Nyquist zone (NZ) 2. In this work the emerging concept of Digital Assistance is pursued to give the receiver access to higher NZs while making no compromise on the SFDR. We will present and discuss post-correction results for two 16-bit high-speed converters from two different vendors at 120 and 125 MSPS, respectively. The proposed system-level post-correction decomposes nonlinearity into a static and a dynamic part. For both ADCs under investigation the degraded SFDR in higher NZs could be improved by up to 15 dB using purely digital linearization technologies, thus increasing the detectability of small signals in the presence of very strong signals or interferers. Near-identical results for both ADCs confirm the general validity of the system-level correction approach.