Design and Analysis of an N-Path Filter with High Out-of-Band Rejection Using Feed-Forward Technique

Abstract

This paper presents an N-path filter with high out-of-band rejection using feed-forward technique. The structure utilizes two four-path filters, one as the main-path and the other as auxiliary-path, and two TIAs to increase the order of the filter from two to four. As a result of this, and due to using two series resistors in the main path, the out-of-band rejection is significantly improved. Analysis and simulations show that the series resistors can be chosen such that the NF degradation is below 2[Formula: see text]dB while the out-of-band rejection is improved by about 20[Formula: see text]dB. Therefore, the trade-off between the insertion-loss and out-of-band rejection is relaxed compared to conventional N-path filter. Also, it is shown that decreasing the size of baseband capacitors improves the NF of the filter. The effect of clock phase-noise on NF of the filter in the presence of strong out-of-band blocker is modeled and simulated.