A blocker-tolerant wideband noise-cancelling receiver with a 2dB noise figure

Abstract

As narrowband off-chip RF filtering is not compatible with the concept of software-defined radio (SDR), an SDR receiver must be designed to tolerate large out-of-band blockers with minimal gain compression and noise figure degradation. A recent circuit tackles this problem by dispensing with the LNA entirely. This mixer-first approach achieves impressive linearity, but at the expense of noise figure and, since such a receiver has no gain prior to down-conversion, the flicker noise corner can be unacceptably high. Other SDR attempts invariably use a noise-cancelling LNA at the front end, which provides wideband matching, however such approaches have either inadequate linearity or display too large a noise for our purposes. In this work, we propose a hybrid frequency-translational, noise-cancelling (FTNC) receiver that employs two separate down-conversion paths to enable noise cancelling with no voltage gain prior to base-band filtering. The resulting design has a sub-2dB noise figure and tolerates 0dBm blockers with no gain back-off, breaking the traditional noise-linearity trade-off common in all receivers.