雙頻帶放大器與陷波濾波器用於WLAN及 WiMAX

Abstract

近年來由於無線通訊的發達，頻段的使用也愈趨頻繁，相對，隨之而來的問題也漸漸浮現，最明顯就是訊號干擾。必須在接收器前端電路設計上，避免系統靈敏度受干擾而大幅降低。通常在接收器前端使用帶通濾波器(Band-pass filter, BPF)降低干擾訊號強度。此外，LNA會加入增益控制功能，來避免靈敏度受干擾而大幅降低。 對於多頻段多模整合系統，仍必須處理相近頻段干擾之嚴重問題。例如在台灣已經流行之WLAN（2.4~2.5GHz）及正極力推動之Wimax（台灣2.5~2.7GHz）由於信號頻段過於相近，幾乎可以說是重疊，隨之而來的干擾是可以相像的，只有BPF無法處理。所以類似的問題將是未來需要研究解決的方向。 所以本論提出了以Active Notch filter的方式，來解決二個頻率過於接近的問題，並利用Varactor來調整LC tank，這樣一來可以使得RFout可以得到WLAN or Wimax的訊號。

Because of the advances of wireless communications in recent years, utilization of radio frequency bands has become more and more frequent. As a result, some issues arise gradually, especially the problem of signal interference. Therefore, it is necessary to avoid loss of system sensitivity to interferences by careful receiver front-end circuitry design. Usually band-pass filter (BPF) is used in receiver front-end to suppress interfering signal strength. Also, LNA provides gain control to avoid loss of sensitivity due to interferences.

For multi-band and multi-mode integrated systems, adjacent band interference is another server problem that needs to be addressed. For example, in Taiwan, the already popular WLAN (2.4~2.5GHz) and emerging WiMAX (2.5~2.7GHz), because of the close and almost overlapping frequency bands, it is clear that the signal interference problem cannot not be handled by only the BPF. This kind of issues point out new research directions.

In this thesis, active notch filter is proposed to resolve issues caused by two signals that are too close in frequency. Also, varactor is utilized to adjust the LC tank such that WLAN or WiMAX signal can be obtained at RF output.