Analysis of the signal transfer and folding in N-Path filters with a series inductance

Lammert Duipmans, R.E. Struiksma, Eric A.M. Klumperink, Bram Nauta, Frank Edward van Vliet

    Research output: Contribution to journalArticleAcademicpeer-review

    33 Citations (Scopus)
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    N-path filters exploiting switched-series-R-C networks can realize high-Q blocking-tolerant band-pass filters. Moreover, their center frequency is flexibly programmable by a digital clock. Unfortunately, the time variant nature of these circuits also results in unwanted signal folding. This paper proves analytically that folding can be reduced and band pass filtering can be improved by adding an inductance in series with the switched-R-C network. In contrast, a shunt capacitor degrades band-pass filter performance. The interaction between the reactive series impedance and the switched capacitors of an N-path filter complicates analysis due to memory effects associated with reactive components. Assuming $N$ identical signal paths with 1/$N$ duty cycle, we show it is possible to solve the set of differential equations, by assuming that the signals in each path only differ in delay. Analytical equations are verified versus simulations, and the benefits in filter properties and reduction in signal folding are demonstrated.
    Original languageEnglish
    Pages (from-to)1-10
    Number of pages10
    JournalIEEE transactions on circuits and systems I: regular papers
    Issue number99
    Publication statusPublished - 1 Jan 2015


    • EWI-25240
    • IR-92400
    • METIS-309629


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