直接射頻數位轉換之正交幅度調變單板接收機

Direct RF to Digital Conversion for Monolithic mQAM Receiver

許家豪(Chia-Hao Hsu)

指導教授 ： 陳朝烈 ； 陳耀煌

崑山科技大學/工程學院/電子工程研究所/碩士(2010年)

摘要

直接將mQAM載波之後的訊號，直接轉換為數位訊號，我們稱之為Direct RF to Digital conversion (RF2D)轉換，用以低成本方式(低功耗、小電路面積)完成單板(monolithic)之接收機，以RF頻率CLK搭配差動式電流放大器與電流模式正反器，將經過RF載波後訊號(mQAM乘以RF載波, 簡稱RF_QAM)轉換成數位訊號，再以高速TSPC組成之計數器來計數RF_QAM訊號中各相位變化間的寬度，藉以判斷出原始mQAM訊號中I與Q訊號組合之相位，再輔以簡易波包檢測電路判斷原始mQAM之振幅，達到數位碼與(相位, 振幅)對應的唯一性，如此便容易查表反轉得到原始數位碼，完成了mQAM 系統之RF2D轉換之數學模型，並以TSMC 0.18μm製程實現16QAM的RF2D單板晶片，採用100MHz的基頻可使資料傳輸率理論值分別可達最高200Mbps以及400Mbps，實際電路達成最高160Mbps，功耗約為55mw。除此之外，透過軟體方式設定計數器的計數初始值，可以彈性調整基頻頻寬，大幅提高接收機相容性，相位變化間的寬度計算採用與RF載波相同頻率的clock訊號來計數，因此主要電路為計數器，mQAM振幅之計算使用簡單濾波電路即可獲得基頻頻率，大幅縮減接收機的設計複雜度也符合軟體定義無線電(Software defined Radio; SDR)的精神目標，且將基頻最大頻率拉為中頻(Intermediate Frequency, IF)，這樣意味著超大頻寬以及極高的資料傳輸率。另外節省了ADC以及DSP的設計，大幅縮小接收機的功耗與面積。

關鍵字

正交幅度調變 ； mQAM ； 直接射頻數位轉換 ； 無線通訊

並列摘要

We propose a direct conversion, called RF2D, from the RF signal modulated by mQAM to digital code for low power, small area, and monolithic receiver realization. A differential Wilson current mirror undertakes saturation amplifier cooperating with a current mode phase detector, a D flip-flop clocking with carrier frequency, converts the RF signal to serial digital pulses whose widths are the phases of the original mQAM baseband signal. Then, high-speed counters based on TSPC, evaluate the widths to digital counts. The association of a digital count and amplitude detection uniquely maps into a digital code. Therefore, a simple lookup-table taking the association as address generates the final output binary code. From the simulation, under 2.56GHz RF carrier we conclude that theoretically 100MHz baseband bandwidth and respective 200Mbps and 400Mbps throughputs are available for QPSK and 16QAM modulations. An 55mW test chip supporting 16QAM and QPSK modulations is implemented using TSMC 0.18μm technology and 40MHz baseband for equivalently 160Mbps throughput is achieved. Software programmable counters allow flexible baseband frequencies for compatibility enhancement. The very reduced but high-performance monolithic RF2D receiver without synthesizer, ADC, and DSP is thus realized to achieve the ultimate software-defined radio (SDR) objective.

並列關鍵字

Quadrature Amplitude Modulation (QAM) ； Direct RF to Digital Conversion ； Wireless Communications

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