A Digitally-Assisted Blocker Resilient RF Receiver for Wideband SAW-less Applications
Babakrpur Nalousi, Esmail
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The demand for integrated wideband surface acoustic wave (SAW)-less receivers that support various wireless communication bands stipulate stringent linearity requirements. Local oscillator (LO) harmonic interferers and out-of-band interferers are two significant sources of signal distortion in wideband SAW-less receivers. Harmonic mixing products and intermodulation products of these interferers, which can be orders of magnitude stronger than the desired signal, fold on the desired signal band, resulting in significant distortion. To improve resilience of such receivers to LO harmonic interferers, a digitally-assisted dual-path receiver with nonuniform LO phases is proposed which employs an adaptive digital equalizer to suppress distortion products. An adaptive minimum mean-squared error (MMSE) harmonic rejection equalizer is developed that minimizes the desired signal distortion in the mean-squared error sense in the presence of harmonic interferers and the correlated noise between the two paths. The proposed receiver performs robust harmonic rejection of any LO harmonic including 7th and 9th using only four uniformly spaced clocks with 25% duty cycle. Although intermodulation products are inherently different in nature from harmonic mixing products, it has been shown that concurrent suppression of both distortions using one MMSE equalizer is feasible in the presence of distinct nonlinear receive chains. A mathematical framework is derived for analyzing signal distortion in the presence of harmonic and out-of-band interferers. This framework models a K-path SAW-less M-phase receiver, which provides sufficient front-end observations to cancel the distortion products. The proposed receiver jointly accounts for distortion products as well as correlated noise of the two paths. Furthermore, the use of passive mixer-ﬁrst receiver topology to sense signals at higher LO harmonics is proposed. The advantages of such a receiver include sensing of multiple bands concurrently and reduced tuning range requirements in the frequency synthesizer. The single and joint harmonic matching performance of a zero-IF M-phase mixer-ﬁrst receiver is analyzed. It is shown that minimum possible return loss for joint matching occurs when the geometric mean of input impedances at the highest and lowest sensing bands equals the antenna impedance. The noise ﬁgure when sensing higher order LO harmonics is shown to result in only modest degradation, with the loss becoming even less with increasing number of LO phases.