多相滤波器的原理及其实现

作为直接变频式低中频接收机中的关键技术之一 ,多相滤波器起着抑制镜像干扰和邻频道干扰的作用 ,它的设计直接影响着整个系统的接收性能。以复数滤波器为例 ,讨论了多相滤波器的基本原理。在此基础上 ,推导出其电路结构形式 ,并实现了一个三阶复数带通滤波器。将该滤波器应用于 90 0 MHz频段低中频接收机中进行测试 ,得到它的幅频特性实验结果 ,中心频率为 2 5 0 k Hz,镜像频率 - 2 5 0 k Hz处镜像抑制达到了 33d B,从而证明了它在低中频接收机中的有效性

Principle and implementation of poly phase filter

The poly phase filter plays an important role as a mirror signal and for rejection of neighbor channel interference as a critical technology in the low IF receiver. This paper discusses the principles and introduces the circuit structure of a poly phase filter using a complex filter as an example. A third order complex filter is implemented and it's amplitude transfer function is presented. The center frequency is 250kHz and the mirror rejection at -250kHz is about 33dB. This result was from a test in which the complex filter was put into a 900MHz low IF receiver to demonstrate the usability of the poly phase filter in a low IF receiver.