834-879MHz UHF 통신시스템 3차 고조파 제거를 위한 Feedforward 기반 액티브 대역통과 필터

This paper descries an active bandpass filter using feedforward structure for improve the channel selectivity of wireless communication system. This avtive bandpass filter is composed of two paths: one path feedforward, the other is feedthrough path. The feedthrough path is composed of a delay control circuit, the feedforward path is composed of a notch filter and PGA. The outputs signal of these two path are added to reject unwanted signals. To perfect reject unwanted signal, the two path should be syncronized each other. Therefore, delay circuit and PGA synchronize phase delay and amplitude of two path signals. The delay controlled 0.2 to 22.5nsec with 0.1nsec step. The PGA gain range is 0 to 15dB with 1dB step. The cut-off frequency response of active bandpass filter is about 40dB/Hz. Moreover, ACLR is about 60dB.