Improved Continuous-Time Delta-Sigma Modulators With Embedded Active Filtering

Continuous-time ΔΣ modulators used in wireless transceivers need to digitize small desired signals that are accompanied by large out-of-band interferers. In such applications, it is desirable that the CTΔΣM have a low-pass signal transfer function whose bandwidth can be specified. Many architectures present themselves as potential candidates to realize such filtering-CTΔΣMs. This work investigates these threads and concludes that a CTΔΣM with an embedded Rauch filter is a compelling design choice. The theory is supported by measurement results from a filtering-CTΔΣM test chip that achieves a peak SNDR of 76.7dB in a 1MHz signal bandwidth. Measurements demonstrate improved power efficiency and out-of-band linearity when compared to prior art.