Analysis and Design of N-Path Filter Offset Tuning in a 0.7–2.7-GHz Receiver Front-End

Kim Östman, Mikko Englund, Olli Viitala, Mikko Kaltiokallio, Kari Stadius, Kimmo Koli, Jussi Ryynänen

Research output: Contribution to journalArticleScientificpeer-review

23 Citations (Scopus)


N-path techniques have become a popular candidate alternative to external pre-selection filtering in wireless receivers. Their main attraction lies in enabling tunable on-chip high- Q filters, with straightforward migration from one CMOS node to another. However, parasitic capacitance at the N-path filter input offsets the bandpass response from the desired center frequency in wideband circuits. In this paper, we focus on an LNA-first receiver and show that the offset at the LNA output varies in magnitude depending on LNA and filter load impedance properties. An offset-tuning approach is then evaluated for its effects on receiver gain and noise and to obtain design guidelines. We propose a digitally controllable implementation that preserves front-end gain and linearity, with a small penalty on receiver NF. A programmable 0.7–2.7-GHz front-end in 40-nm CMOS verifies the functionality. At 1.7 GHz, the front-end has a gain of 37 dB, a NF of 5.2 dB, and an out-of-band IIP3 of + 1 dBm.

Original languageEnglish
Article number6926874
Pages (from-to)234-243
Number of pages10
Issue number1
Publication statusPublished - Jan 2015
MoE publication typeA1 Journal article-refereed


  • Blockers
  • circuit optimization
  • CMOS
  • complex filtering
  • linearity
  • low-noise amplifiers
  • N-path filtering
  • quadrature
  • receivers
  • RF front-ends


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