A phase-noise and spur filtering technique using reciprocal-mixing cancellation

Abstract

Recent passive-mixer-based architectures, such as [1], have shown that blockers as large as 0dBm can be tolerated without excessive gain compression. However, even in a perfectly linear receiver, reciprocal mixing of the blocker with LO phase noise deposits additive noise on the wanted signal, as shown in Fig. 5.3.1. This is an inevitable limitation to any mixer-based receiver. Assuming that the blocker experiences no passive RF filtering, the noise figure of such a receiver in the presence of a given blocker is only lowered through improving the LO phase noise. To overcome this challenge, most wireless receivers use LC-oscillators that despite their superior phase noise to ring oscillators [2], still consume a large portion of the radio power. As the quality factor of on-chip resonators does not scale with technology, the phase noise of an LC-oscillator can only be improved by consuming more power, while the benefits of circuit innovation are fundamentally limited [3]. Although increasing current helps, it does come at a cost, and is ultimately limited by the maximum allowable amplitude, and how reliably small inductor values can be fabricated without Q-degradation. In this paper, we propose a mixed-signal reciprocal-mixing cancellation technique that leads to a substantial reciprocal-mixing noise figure improvement independent of the LO phase noise.