Reciprocal mixing and inherent nonlinearity in N-path filters
P. van der Kamp (TU Delft - Electrical Engineering, Mathematics and Computer Science)
LCN de Vreede – Mentor (TU Delft - Electronics)
M Babaie – Graduation committee member (TU Delft - Electronics)
M.A. Montazerolghaem – Coach (TU Delft - Electronics)
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Abstract
N-path filters promise to miniaturize RF receivers by replacing various fixed off-chip filters with a single programmable on-chip filter. This research investigates some of the issues of receivers with N-path filters under strong blocker conditions: reciprocal mixing and inherent nonlinearity. First, a technique for reciprocal mixing cancellation is explored and shown to be impossible using only mixers and baseband impedances. Second, the inherent nonlinearity of both bandpass and notch N-path filters are simulated and modelled. To validate this approach, a highly linear receiver is proposed and designed in 40nm CMOS. The receiver has a bandpass common gate architecture, with a notch filter in the feedback path, improving linearity. The filter is isolated using buffers, improving LO leakage. The common gate stage is IM3 compensated to obtain good
linearity (OOB IIP3 >20 dBm).