引言

　　在某型雷達(dá)信號(hào)處理系統(tǒng)中，要求由上位機(jī)(普通PC)實(shí)時(shí)監(jiān)控雷達(dá)系統(tǒng)狀態(tài)并采集信號(hào)處理機(jī)的關(guān)鍵變量，這就要求在處理機(jī)與上位機(jī)之間建立實(shí)時(shí)可靠的連接。同時(shí)，上位機(jī)也能對(duì)信號(hào)處理板進(jìn)行控制，完成諸如處理機(jī)復(fù)位、DSP程序動(dòng)態(tài)加載等功能。實(shí)驗(yàn)中，處理機(jī)和上位機(jī)之間的數(shù)據(jù)傳輸距離不小于8m。在這種前提下，計(jì)算機(jī)上現(xiàn)有的串口、并口顯然不能滿足要求，而USB2．0接口工作在高速模式時(shí)傳輸距離只有3m，其它諸如以太網(wǎng)傳輸?shù)膶?shí)時(shí)性難于滿足要求，光纖通道傳輸?shù)臉?gòu)建成本又太高。基于此，本文提出了一種采用LVDS高速串行總線技術(shù)的傳輸方案。

　　數(shù)據(jù)傳輸系統(tǒng)方案

　　由于系統(tǒng)要求傳輸距離大于8m，需采用平衡電纜。對(duì)于兩端LVDS接口，可以采用ASIC和FPGA兩種方式實(shí)現(xiàn)。由于Xilinx公司生產(chǎn)的Virtex-II系列FPGA直接支持LVDS電平標(biāo)準(zhǔn)，本系統(tǒng)采用XC2V250實(shí)現(xiàn)，這不僅省去了專用LVDS電平轉(zhuǎn)換芯片，節(jié)省了成本，而且可以將系統(tǒng)中其它控制邏輯集成在單個(gè)FPGA芯片內(nèi)，從而降低了PCB設(shè)計(jì)的難度，提高了系統(tǒng)的集成度和可靠性。另外，收發(fā)接口邏輯采用FPGA，可以在使用過(guò)程中根據(jù)需要重新配置傳輸方向，以動(dòng)態(tài)地改變收發(fā)通道的數(shù)目，大大增強(qiáng)了系統(tǒng)的可重構(gòu)能力。

　　整個(gè)數(shù)據(jù)傳輸系統(tǒng)框圖如圖1所示。由于數(shù)據(jù)傳輸是雙向的，信號(hào)處理板和PCI板都有并／串轉(zhuǎn)換發(fā)送模塊和串／并轉(zhuǎn)換接收模塊(均在FPGA內(nèi)實(shí)現(xiàn))，兩塊板卡通過(guò)平衡電纜連接。此外，在信號(hào)處理板上，DSP處理機(jī)通過(guò)外部總線向FPGA發(fā)送緩存區(qū)內(nèi)寫(xiě)入數(shù)據(jù)，F(xiàn)PGA通過(guò)DSP的主機(jī)口完成與DSP存儲(chǔ)空間的數(shù)據(jù)交換。在PCI板上，F(xiàn)PGA通過(guò)PCI控制器和主機(jī)進(jìn)行數(shù)據(jù)交換。系統(tǒng)工作原理可表述如下：DSP處理機(jī)將處理結(jié)果通過(guò)外部總線輸出到FPGA緩沖存儲(chǔ)器內(nèi)，在FPGA內(nèi)完成數(shù)據(jù)的并／串轉(zhuǎn)換，并通過(guò)LVDS串行接口發(fā)送出去。數(shù)據(jù)通過(guò)平衡電纜傳輸至上位機(jī)接收卡。在上位機(jī)接收卡內(nèi)，數(shù)據(jù)經(jīng)串／并轉(zhuǎn)換后，送至PCI接口控制電路。上位機(jī)輸出數(shù)據(jù)到DSP處理板的過(guò)程則相反。由于系統(tǒng)要求數(shù)據(jù)傳輸上行數(shù)據(jù)率小于下行數(shù)據(jù)率，設(shè)計(jì)中上行數(shù)據(jù)傳輸通道數(shù)為1，下行數(shù)據(jù)通道數(shù)是4。在傳輸距離大于8m的情況下，實(shí)際單通道數(shù)據(jù)傳輸速率達(dá)到264Mbps。



　　LVDS并／串轉(zhuǎn)換實(shí)現(xiàn)

　　由于FPGA是通過(guò)DSP處理機(jī)的外部總線獲得數(shù)據(jù)的，其數(shù)據(jù)形式是并行的，所以發(fā)送前應(yīng)將其轉(zhuǎn)換為串行比特流。FPGA內(nèi)實(shí)現(xiàn)并／串轉(zhuǎn)換和串行發(fā)送功能的模塊HSTX的原理框圖如圖2所示。



　　由圖2可以看出，該模塊有3個(gè)輸入信號(hào)。分別為時(shí)鐘輸入CLK、幀同步信號(hào)TFR和并行數(shù)據(jù)TCH1[7：0]。其中，CLK頻率為33MHz，經(jīng)過(guò)數(shù)字時(shí)鐘管理器(DCM)鎖相倍頻后得到串行模塊內(nèi)部時(shí)鐘CLK1X(33MHz)、CLK4XR(33×4=132MHz)和CLK4XF(33×4=132MHz)，其中CLK4XR與CLK4XF反相，與CLK1X同相。輸出為三組差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" 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title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" 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title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)" title="差分信號(hào)">差分信號(hào)">差分信號(hào)，分別為串行數(shù)據(jù)TCH1[P：N]、串行時(shí)鐘TCLK[P：N]和串行幀同步信號(hào)TFR[P：N]。輸入時(shí)鐘CLK信號(hào)上升沿有效，時(shí)鐘上升沿時(shí)，若幀同步信號(hào)為高電平，則鎖存輸入數(shù)據(jù)TCH1[7：O]，延時(shí)一個(gè)時(shí)鐘周期開(kāi)始發(fā)送。輸出的發(fā)送時(shí)鐘TCLK[P：N]為132MHz，雙沿有效。輸出串行數(shù)據(jù)采用小終端模式，數(shù)據(jù)低位LSB在前，幀同步信號(hào)TFR[P：N]輸出比特序列11110000，用于供接收端同步。

　　如圖2所示，串行發(fā)送模塊主要由LOAD_GEN、OUT_DATA、OUT_FR、OUT_CLK4個(gè)模塊組成。LOAD_GEN模塊用來(lái)產(chǎn)生并／串轉(zhuǎn)換時(shí)加載數(shù)據(jù)的選通脈沖。OUT_DATA模塊采用移位寄存器實(shí)現(xiàn)數(shù)據(jù)并／串轉(zhuǎn)換。而OUT_FR和OUT_CLK模塊分別用來(lái)產(chǎn)生串行幀同步信號(hào)和串行時(shí)鐘信號(hào)。這些模塊均使用硬件描述語(yǔ)言VHDL設(shè)計(jì)完成。

　　LVDS傳輸電路設(shè)計(jì)

　　由于LVDS總線的傳輸速率達(dá)到264Mbps，對(duì)PCB布線等方面要求特別高。本文利用高速電路仿真分析工具——Mentor Graphics公司的HyperLynx，對(duì)LVDS傳輸電路進(jìn)行了仿真設(shè)計(jì)，包含傳輸線阻抗設(shè)計(jì)、端接匹配、差分信號(hào)布線。同時(shí)考慮了接插件和傳輸電纜的選擇對(duì)數(shù)據(jù)傳輸?shù)挠绊憽?br />
　　LVDS信號(hào)的電壓擺幅只有350mV，為電流驅(qū)動(dòng)的差分信號(hào)工作方式，最長(zhǎng)的傳輸距離可以達(dá)到10m以上。為了確保信號(hào)在傳輸線中傳播時(shí)，不受反射信號(hào)的影響，LVDS信號(hào)要求傳輸線阻抗受控，差分阻抗為100。本系統(tǒng)應(yīng)用中，利用高速電路仿真分析工具，通過(guò)合理的設(shè)置層疊厚度和介質(zhì)參數(shù)，調(diào)整走線的線寬和線間距，計(jì)算出單線和差分阻抗結(jié)果，來(lái)達(dá)到阻抗控制的目的。
LVDS信號(hào)的拓?fù)淇梢允屈c(diǎn)到點(diǎn)單向，點(diǎn)到點(diǎn)雙向或總線型(multi—drop)。無(wú)論哪種應(yīng)用，都需要在接收端進(jìn)行端接匹配。匹配阻抗值等于差分阻抗，典型值為100。匹配電阻在這里主要起到吸收負(fù)載反射信號(hào)的作用，因此，要求距離接收端盡量靠近。在本系統(tǒng)中，利用FPGA片內(nèi)的數(shù)控阻抗(Digitally Controlled Impedance)，直接配置FPGA內(nèi)部端接阻抗值，在FPGA內(nèi)部實(shí)現(xiàn)端接匹配。這樣做不僅可以方便修改端接阻抗值大小，使端接電阻很好地匹配，而且端接電阻與接收端非常靠近。

　　差分信號(hào)的布線是整個(gè)傳輸電路設(shè)計(jì)的難點(diǎn)。一般來(lái)說(shuō)，按照阻抗設(shè)計(jì)規(guī)則進(jìn)行差分信號(hào)布線，就可以確保LVDS信號(hào)質(zhì)量。在實(shí)際布線當(dāng)中，LVDS差分信號(hào)布線應(yīng)遵循以下原則：

1、差分對(duì)應(yīng)該盡可能地短、走直線、減少布線中的過(guò)孔數(shù)，差分對(duì)內(nèi)的信號(hào)線間距必須保持一致，避免差分對(duì)布線太長(zhǎng)，出現(xiàn)太多的拐彎。

2、差分對(duì)與差分對(duì)之間應(yīng)該保證10倍以上的差分對(duì)間距，減少線間串?dāng)_。必要時(shí)，在差分對(duì)之間放置隔離用的接地過(guò)孔。

3、LVDS差分信號(hào)不可以跨平面分割。盡管兩根差分信號(hào)互為回流路徑，跨分割不會(huì)割斷信號(hào)的回流，但因?yàn)槿鄙賲⒖计矫娑鴮?dǎo)致阻抗的不連續(xù)。

4、盡量避免使用層間差分信號(hào)。在PCB板的實(shí)際加工過(guò)程中，由于層疊之間的層壓對(duì)準(zhǔn)精度大大低于同層蝕刻精度，以及層壓過(guò)程中的介質(zhì)流失，層間差分信號(hào)不能保證差分線之間間距等于介質(zhì)厚度，因此會(huì)造成層間差分對(duì)的差分阻抗變化。因此建議盡量使用同層內(nèi)的差分。

5．在設(shè)計(jì)阻抗時(shí)，盡量設(shè)計(jì)成緊耦合方式，即差分對(duì)線間距小于或等于線寬。

　　此外，在LVDS傳輸電路設(shè)計(jì)當(dāng)中應(yīng)當(dāng)選用適合差分信號(hào)的高速接插件，一方面，接插件的特征參數(shù)能夠與LVDS信號(hào)阻抗匹配，通過(guò)接插件的信號(hào)畸變很小；另一方面，能夠提供足夠的布線空間，設(shè)計(jì)PCB走線寬度和間距。例如AMP公司的Z—PACK HS3系列接插件，在電氣性能方面，比較適合高速LVDS信號(hào)互連。

　　本系統(tǒng)采用平衡電纜實(shí)現(xiàn)長(zhǎng)距離傳輸，然而，由于LVDS特殊的阻抗匹配要求和極低的時(shí)序偏置要求，傳統(tǒng)的電纜不能用于LVDS數(shù)據(jù)傳輸。試驗(yàn)證實(shí)雙絞線電纜性能最優(yōu)。短距離(大約0．5m)應(yīng)用時(shí)CAT3平衡雙絞線電纜效果最佳。而高于0．5m以及數(shù)據(jù)率大于500MHz時(shí)，CAT5平衡電纜效果最好。
結(jié)語(yǔ)

　　本文實(shí)現(xiàn)的高速數(shù)據(jù)傳輸系統(tǒng)，已成功應(yīng)用于某雷達(dá)信號(hào)處理機(jī)和上位機(jī)之間的數(shù)據(jù)傳輸，傳輸距離大于8m，單個(gè)通道數(shù)據(jù)傳輸速率達(dá)到264Mbps，5個(gè)數(shù)據(jù)通道傳輸速率總共達(dá)1．32GbpS，傳輸過(guò)程穩(wěn)定。