A Harmonic Rejecting N-Path Filter with Harmonic Gain Calibration Technique

Abstract

In this paper, an improved harmonic rejecting N-path filter with a circuit-level structure is proposed. A different set of mixing functions is introduced to conventional N-path filters. Systematic analysis shows that the mixing functions have the benefits of harmonic rejection at the radio frequency node. An 8-path circuit-level structure is proposed, and a harmonic gain calibration technique is introduced to calibrate the errors due to the process variation and mismatch. The proposed 8-path filter is designed and simulated under the 65-nm CMOS technology and achieves 17–$29\text{dB}$ gain with a $2\mathrm{nd}$ harmonic rejection ratio of 24–$31\text{dB}$, $3\mathrm{rd}$–$6\mathrm{th}$ harmonic rejection ratio of 35–$60\text{dB}$, a frequency range of 0.1–$1\text{GHz}$, and a noise figure of 3.8–$4.9\text{dB}.$