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標題: 應用於IEEE 802.11b傳送器濾波電路之實現
Implementation of Shaping Filter for IEEE 802.11b Transmitter
作者: 呂文玉
關鍵字: 濾波器;FIR filter;IEEE 802.11b;Nyquist;Sub-expression sharing;CSD
出版社: 電機工程學系
在這篇論文中,我們將介紹應用於無線區域網路中IEEE 802.11符合Nyquist條件的的根上升餘弦濾波器。這個濾波器是一個典型依係數塑型的有限脈衝響應(FIR)濾波器。我們採用這個濾波器,係由於降低符號間干擾與將送入類比數位轉換器平滑化的因素。IEEE 802.11是使用直接序列展頻及差動二相/正交相移鍵調變技術,並使用互補碼鍵來有效的提供不同的資料速率,文中也會討論到其發射接收器的架構。
為了完成這個濾波器,我們將使用二補數與典型的符號數字取代傳統數字系統,加上提出子式表達及鄰近係數分享的方法使濾波器能較為完美,在架構上並利用係數對稱的原理,將硬體縮減為原來的一半。在邏輯閘層模擬結果,輸出資料速率可達71.43MHz(系統要求為44MHz),使用Avant! 0.35um cell library合成的晶片面積為11259的單位邏輯閘。

A Nyquist digital Filter- Root Raised Cosine filter for IEEE 802.11b of WLAN BBP will be presented in this thesis. The shaping filter is a typical FIR Filter whose passband shape is set by taps coefficients. We adopt the filter because it can reduce the ISI phenomenon and smoothen these data bits before sending to the DAC. The IEEE 802.11b Wireless LAN adopts Direct Sequence Spread Spectrum (DSSS) technology. The differential phase shift keying modulation schemes (DBPSK/DQPSK) along with Complementary Code Keying (CCK) are used to provide a variety of data rates. The transceiver structure will be introduced briefly.
In this thesis, various number systems such as 2's complement and CSD will be discussed. Besides, sub-expression sharing and adjacent coefficient sharing will be addressed to optimize the filter. Since the impulse response of the FIR filter has symmetric coefficients about the center coefficient, the FIR filter with linear phase can reduce hardware cost by half. In gate-level simulation, the input data rate could reach 71.43 MHz (14ns), which can meet the system specification of 44MHz. The total area is 11259 gate counts using Avant! 0.35um cell library.
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