An Ultra-Narrowband N-path Notch Filter for NB-IoT Applications
Jianbin Liu, Zhihua Wei, Kun Li, Pei‐Ling Chi, Tao Yang · 2024
In this paper, an ultra-narrowband N-path notch filter for Narrowband Internet of Things (NB-IoT) applications is proposed. Conventional N-path notch filters rely mostly on adjusting the baseband capacitance to meet the performance requirements of narrowband notch bandwidth (BW), resulting in excessive capacitance area. In contrast, this paper presents an innovative approach to optimize the notch bandwidth in terms of both clock duty cycle and switch size, and combines it with an LC-matching method to reduce the impact on the pass-band insertion loss. The ultra-narrowband notch filter is fabricated using a 55nm CMOS process. Measurement results show that it successfully achieves an extremely narrow BW of only 180 kHz with a compact overall size of 1.1mm2. The measured maximum rejection is 22 dB and pass-band return loss keeps better than 13 dB under the adjustable frequency range of 1.79 to 1.88GHz.