射頻前端電路優化應用於IMT頻段

Optimization of RF front end circuit for IMT-Band

巫奇紘(Chi-hung Wu)

指導教授 ： 林嘉慶

國立中央大學/資訊電機學院/通訊工程研究所碩士在職專班/碩士(2012年)

摘要

本論文主要目的，致力於減少發射機之射頻前端電路元件而進一步能夠節省PCB面積及降低成本，其工作頻率範圍介於發射(1.92GHz~1.98GHz)和接收(2.11GHz~2.17GHz)頻段之間，為WCDMA和LTE系統規範眾多頻帶之一，其接收器必須在減少發射電路中的表面聲波濾波器下還能夠符合3GPP之BER測試規範，並且能在Rohde & Schwarz的無線綜合測試儀器(CMU-200)量測到的靈敏度為-106.7dB以下。本論文將利用SMD(surface mount device, SMD)元件及PCB (2-2-2)多層板製作，經各元件規格量測及性能確認後，再予以整合至PCB基板，且由理論推導問題中，尋找較佳之解決方法，做為日後在設計電路時之流程及準則，而達到追求低成本及體積小之電路。
本研究之發射機架構裡的射頻前端電路包含有天線開關、功率放大器、表面聲波濾波器、雙工器及收發機之電路構成，其中用在減少發射所散射出來的雜訊所使用的表面聲波濾波器，在尚未去除前，由系統架構推算出整體雜訊指數為5.5dB，經由轉換公式得到接收靈敏度為-112.2dBm；而當移除表面聲波濾波器時，此時推算出整體雜訊指數為8.3dB，經由轉換公式得到接收靈敏度為-109.4dBm，此時很明顯看出因發射端的雜訊影響到接收端所看到的雜訊指數上升，使得靈敏度下降；而用於雙工器的效能提昇時，推算出整體雜訊指數為5.8dB，經由轉換公式得到接收靈敏度為-111.9dBm，由數據看出此方法能有效改善雜訊的干擾，使得接收靈敏度能接近於增加了表面聲波濾波器時所得到的效能。
於PCB整合本論文中的前端電路元件後，在使用Rohde & Schwarz的CMUgo之軟體直接經由 RF 連接儀器CMU-200進行測試量測整個接收頻段(2.11GHz~2.17GHz)中的每個頻道(Channel)所得到結果：在尚未移除表面聲波濾波器時所量測到的接收靈敏度平均值為-111.94dBm；當移除表面聲波濾波器時所量測到的接收靈敏度平均值為-109.59dBm；用於雙工器的效能提昇時所量測到的接收靈敏度平均值為-111.75dBm。由此量測結果看出和推導結果所得到之結論略為相同。

關鍵字

靈敏度 ； 射頻前端 ； 雙工器 ； 表面聲波濾波器

並列摘要

In this thesis, the SAW filter of RF front end circuit was eliminated, it would save area on the PCB as well as cost. The transmit frequency lies between 1.92 and 1.98GHz, receiver frequency lies between 2.11 and 2.17GHz, which meets the bandwidth specifications for WCDMA and LTE systems. According to the 3GPP specification, the Rx sensitivity within BER test of CMU-200 (Rohde & Schwarz) cannot exceed -106.7dBm. The research would use surface mount device (SMD) and a multilayer PCB to make sub-circuits. After the elements of sub-circuits have passed measurement and performance tests, we combine the elements on multilayer PCB. Low cost and small size are to be expected from circuits. Our design seeks to implement the best solution.
The transceiver of the RF front end circuit includes antenna switch module, power amplifier, SAW filter, duplexer and transceiver. Assume, the SAW filter is existed from the Tx chain and the noise figure is 5.5dB. The receiver sensitivity is -112.2dBm; Assume, the SAW filter is removed from the Tx chain and the noise figure is 8.3dB. The receiver sensitivity is -109.4dBm. Tx to Rx desensitization occurs because the transmit noise in the Rx band leaks into the Rx chain and effectively increases the noise figure of the Rx; the perspective of improving the performance of the duplexer from the Tx and the noise figure is 5.8dB. The receiver sensitivity is -111.9dBm.
After the integration test combining all the elements of sub-circuits, the result of all Rx channel measurement covering 2.11 to 2.17GHz for IMT band.
Sensitivity measurements can be made by using the CMU-200.The full suite of Rohde & Schwarz CMUgo measurement is available for analysis. When the SAW filter is existed, the mean value of receiver sensitivity is -111.94dBm. When the SAW filter is removed, the mean value of receiver sensitivity is -109.59dBm. Improving the performance of the duplexer, the mean value of receiver sensitivity is -111.75dBm. From the above-mentioned, measurement values and equation value are the same result.

並列關鍵字

duplexer ； SAW filter ； front end ； sensitivity ； IMT-Band

參考文獻

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