Breaking the Trade-Off between Bandwidth and Close-in Blocker Attenuation in an N-Path Filter

A unique property of two-path filter is exploited to reject close-in blocker bands near a desired receiver band. It is based on the observation that each path in a two-path filter averages one half-cycle of the input carrier. If the carrier and the filter's clocks have same frequencies, the average over half-cycle of a sinusoid depends on the phase difference between the clock and the input. A 90
^o
or 270
^o
phase difference can result in a zero average, and potentially a perfect carrier suppression. Since this principle of blocker suppression is based on a relative phase relationship between the clock and the blocker, and not a relative frequency separation between the bands, it is shown to break the trade-offs plaguing the pass-band width of a filter and the extent of close-in blocker suppression. A digitally auto-tuned loop that calibrates the 2-path clocks to the desired phase is proposed. The proposed two-path architecture is shown to attenuate close- in blockers more efficiently than the traditional bandpass and bandstop N-path filters.