信號發生器簡介

    源(yuan)技(ji)術發(fa)祥于電(dian)力電(dian)子技(ji)術，通(tong)常認為1960年左(zuo)右(you)是電(dian)力電(dian)子技(ji)術的(de)起源(yuan)，其發(fa)展由(you)現代(dai)追(zhui)溯回上世紀，分別經(jing)歷了變(bian)頻器(qi)時(shi)代(dai)、逆(ni)變(bian)器(qi)時(shi)代(dai)和整(zheng)流器(qi)時(shi)代(dai)。

    信(xin)(xin)(xin)號(hao)(hao)源是一種常用(yong)(yong)(yong)于(yu)(yu)各(ge)大實(shi)驗(yan)室及教學等(deng)(deng)場(chang)所，能(neng)為其(qi)(qi)他設備提供(gong)低(di)噪聲(sheng)的(de)(de)(de)(de)標(biao)準電信(xin)(xin)(xin)號(hao)(hao)的(de)(de)(de)(de)供(gong)電儀器，信(xin)(xin)(xin)號(hao)(hao)源部(bu)分采(cai)(cai)(cai)用(yong)(yong)(yong)多級(ji)(ji)穩(wen)(wen)(wen)(wen)壓(ya)方(fang)法，對傳(chuan)統信(xin)(xin)(xin)號(hao)(hao)源的(de)(de)(de)(de)開關穩(wen)(wen)(wen)(wen)壓(ya)或線(xian)性穩(wen)(wen)(wen)(wen)壓(ya)結構進行優(you)化改進。其(qi)(qi)中(zhong)前級(ji)(ji)穩(wen)(wen)(wen)(wen)壓(ya)采(cai)(cai)(cai)用(yong)(yong)(yong)與(yu)開關穩(wen)(wen)(wen)(wen)壓(ya)功(gong)(gong)能(neng)相(xiang)近的(de)(de)(de)(de)工頻變壓(ya)器，主要實(shi)現交流信(xin)(xin)(xin)號(hao)(hao)與(yu)直(zhi)流信(xin)(xin)(xin)號(hao)(hao)的(de)(de)(de)(de)轉換(huan)，再(zai)經整流濾波進行初步(bu)穩(wen)(wen)(wen)(wen)壓(ya)；而后(hou)級(ji)(ji)穩(wen)(wen)(wen)(wen)壓(ya)利用(yong)(yong)(yong)線(xian)性穩(wen)(wen)(wen)(wen)壓(ya)的(de)(de)(de)(de)高精(jing)度低(di)噪聲(sheng)，對前級(ji)(ji)穩(wen)(wen)(wen)(wen)壓(ya)輸出的(de)(de)(de)(de)直(zhi)流信(xin)(xin)(xin)號(hao)(hao)做二次穩(wen)(wen)(wen)(wen)壓(ya)處理，核(he)心控制(zhi)部(bu)分采(cai)(cai)(cai)用(yong)(yong)(yong)ARM處理器芯片與(yu)FPGA芯片共(gong)同組成的(de)(de)(de)(de)多核(he)心控制(zhi)方(fang)案(an)，對于(yu)(yu)普遍采(cai)(cai)(cai)用(yong)(yong)(yong)的(de)(de)(de)(de)單(dan)核(he)ARM核(he)心或單(dan)核(he)FPGA核(he)心更具有(you)優(you)勢。其(qi)(qi)中(zhong)ARM處理器的(de)(de)(de)(de)主要功(gong)(gong)能(neng)為信(xin)(xin)(xin)號(hao)(hao)采(cai)(cai)(cai)集獲取、信(xin)(xin)(xin)號(hao)(hao)處理及濾波等(deng)(deng)功(gong)(gong)能(neng)，FPGA則控制(zhi)數字(zi)信(xin)(xin)(xin)號(hao)(hao)與(yu)模擬信(xin)(xin)(xin)號(hao)(hao)之(zhi)間的(de)(de)(de)(de)轉換(huan)與(yu)輸出等(deng)(deng)功(gong)(gong)能(neng)，兩(liang)者相(xiang)互獨立卻又相(xiang)輔相(xiang)成，共(gong)同承擔(dan)模塊的(de)(de)(de)(de)核(he)心控制(zhi)功(gong)(gong)能(neng)。

    信號發生(sheng)器(qi)技術原理

    頻(pin)率(lv)(lv)合成技(ji)(ji)(ji)術是現在(zai)最為廣泛(fan)使(shi)用(yong)(yong)的(de)(de)直(zhi)接數(shu)字合成技(ji)(ji)(ji)術（DDS），由(you)于其具備的(de)(de)低(di)相(xiang)位(wei)(wei)噪聲(sheng)與高分(fen)辨率(lv)(lv)特性(xing)，并(bing)且在(zai)輸出不(bu)同頻(pin)率(lv)(lv)時(shi)DDS能(neng)(neng)夠(gou)保(bao)持連續的(de)(de)相(xiang)位(wei)(wei)。這種技(ji)(ji)(ji)術特性(xing)使(shi)其能(neng)(neng)夠(gou)方便實現相(xiang)位(wei)(wei)、頻(pin)率(lv)(lv)和幅(fu)度(du)(du)調(diao)制，使(shi)得其廣泛(fan)應用(yong)(yong)在(zai)現代信(xin)號發(fa)生(sheng)器研究(jiu)領域。直(zhi)接數(shu)字頻(pin)率(lv)(lv)合成基本結構圖(tu)如圖(tu)1-1所示。其主要由(you)時(shi)鐘(zhong)發(fa)生(sheng)器，數(shu)據存儲(chu)，相(xiang)位(wei)(wei)累(lei)加器以及DAC數(shu)模轉(zhuan)換合成技(ji)(ji)(ji)術等組成。主要原理是將(jiang)信(xin)號的(de)(de)幅(fu)度(du)(du)值取樣量化為不(bu)同數(shu)值后按照(zhao)不(bu)同的(de)(de)相(xiang)位(wei)(wei)存儲(chu)進波形查找(zhao)表，然后按照(zhao)相(xiang)關時(shi)序在(zai)每(mei)個時(shi)鐘(zhong)的(de)(de)上升沿，通(tong)過讀(du)取相(xiang)關的(de)(de)相(xiang)位(wei)(wei)地址來(lai)讀(du)取幅(fu)度(du)(du)值最后進行數(shu)模轉(zhuan)換輸出。

    圖1-1DDS結構框圖

    直(zhi)接數(shu)(shu)(shu)字頻率(lv)(lv)合(he)成(cheng)是以奈奎(kui)斯特抽(chou)樣定理和數(shu)(shu)(shu)字頻率(lv)(lv)合(he)成(cheng)為(wei)基(ji)(ji)礎。直(zhi)接數(shu)(shu)(shu)字頻率(lv)(lv)合(he)成(cheng)是已知經過(guo)量(liang)化并(bing)存儲于(yu)波(bo)形(xing)(xing)ROM表(biao)中(zhong)(zhong)的(de)數(shu)(shu)(shu)據，采(cai)用相位(wei)累加的(de)方法把數(shu)(shu)(shu)據表(biao)中(zhong)(zhong)的(de)數(shu)(shu)(shu)據取出在(zai)經過(guo)數(shu)(shu)(shu)模轉換和低通濾波(bo)還原模擬(ni)信(xin)(xin)(xin)號(hao)的(de)過(guo)程。構框圖中(zhong)(zhong)f為(wei)系(xi)統基(ji)(ji)準(zhun)時(shi)鐘，通過(guo)設定不同的(de)頻率(lv)(lv)控(kong)制字K使得每(mei)經過(guo)一(yi)(yi)個時(shi)鐘脈沖上升沿(yan)N位(wei)相位(wei)累加寄存器的(de)值(zhi)增加K，這(zhe)個值(zhi)作為(wei)波(bo)形(xing)(xing)數(shu)(shu)(shu)據表(biao)的(de)地址信(xin)(xin)(xin)號(hao)，在(zai)對(dui)應(ying)時(shi)鐘的(de)上升沿(yan)對(dui)波(bo)形(xing)(xing)存儲器進行查表(biao)輸(shu)出相應(ying)的(de)數(shu)(shu)(shu)字信(xin)(xin)(xin)號(hao)。數(shu)(shu)(shu)字量(liang)對(dui)應(ying)波(bo)形(xing)(xing)的(de)某(mou)一(yi)(yi)個幅(fu)度值(zhi)，波(bo)形(xing)(xing)數(shu)(shu)(shu)據ROM表(biao)的(de)輸(shu)出值(zhi)經過(guo)數(shu)(shu)(shu)模轉換形(xing)(xing)成(cheng)一(yi)(yi)定頻率(lv)(lv)的(de)模擬(ni)信(xin)(xin)(xin)號(hao)，通過(guo)低通濾波(bo)后輸(shu)出平滑(hua)的(de)模擬(ni)信(xin)(xin)(xin)號(hao)。