分時多工個人通信設備其射頻電路對本身語音信號干擾之研究

Abstract

目前無線技術在分配使用者頻寬方面，有分時多工(TDMA)，編碼多工 (CDMA)，分頻多工(FDMA)等等。基於成本較低以及容易實現的考量，分時多工仍是主要的實現方式。但其切割時間的特性，容易導致個人通信設備，例如GSM，PHS 手機，或是最近WIFI 手機，其本身的射頻電路去干擾鄰近電路的語音信號，造成令人困擾的音頻噪音。 本研究以無線網路(802.11g)為實驗平台，研究其射頻電路工作於分時多工時，對鄰近語音處理電路之影響。本研究首先探討傳導干擾以及輻射干擾機制；繼而尋求降低射頻電路干擾能力，以及增強音頻電路干擾耐受度的方法。 我們發現射頻功率放大器動作時，其固有的負載效應，使得供應電源產生漣波，進而影響音頻輸入端的偏壓，是傳導干擾的主因。再者，由於差動放大器的射頻整流現象，間歇性的射頻信號進入音頻線路會造成音頻差動放大器直流準位偏移進而產生噪音。

To arrange communication user resource over air, we use the method of TDMA, CDMA, FDMA and so on. For the reason of cost effectiveness and relative easy implementation, TDMA is still the most used technique such as GSM,PHS and WiFi. As its operation requires periodic switching on-and-off of the RF front end at a rate in the audio frequency range, TDMA system has a possibility to interfering its own audio signal and generates annoy noise from itself easily. An 802.11(Wi-Fi) platform is need in this thesis for the study of effects of RF circuits on adjacent audio signal processing circuits. First, we investigate the conduction and radiation interference mechanisms. Then, we evaluate the methods of decreasing emission capability of the RF circuits and enhancing immunity of the audio circuits. We found the ripple voltage caused by RF PA loading effect can affect audio input circuit to generating noise, in addition, the RF rectification phenomenal on differential amplifier of audio circuit is root cause of EMI, this perceivable noise would be generated whenever audio circuit is subjected to RF signal which is amplitude modulated at an audio frequency.