Quantization Noise Upconversion Effects In Mixer-First Direct Delta-Sigma Receivers

In this paper, we investigate the application of the direct Delta sigma receiver (DDSR) concept in a mixer-first architecture. Specifically, we analyze the degrading effects of quantization noise (Q(n)) upconversion on DDSR sensitivity, which is a major concern in mixer-first DDSR architecture. We demonstrate that with the chosen approach, the mixer-first architecture is suitable for the DDSR despite the potential challenges arising from Q(n) upconversion. A systematic modeling and understanding of Q(n) upconversion effects is presented, which lead to simple design guidelines. The results demonstrate that a first-order low-pass Q(n) filtering is sufficient in most cases for mixer-first DDSR implementations. Based on analytical results, we design a transistor-level mixer-first DDSR by merging the functionality of N-path capacitors both as channel select and Q(n) filters. Simulations performed in a 28-nm complementary metal-oxideUsemiconductor (CMOS) process show a mere 1.5-dB degradation from maximum signal-to-noise and distortion ratio (SNDR) for the worst-case scenarios arising from Q(n) upconversion effects, validating the chosen approach.