一、基于單片機的信號發生器設計方案
信號(hao)(hao)發生器用于(yu)調(diao)節射頻匹配電路，可以自行設計(ji)，一般普通的(de)信號(hao)(hao)發生器需要(yao)輸出正弦(xian)波(bo)、方波(bo)、三角波(bo)以及鋸齒(chi)波(bo)等(deng)信號(hao)(hao)，可通過按鍵調(diao)節信號(hao)(hao)的(de)頻率(lv)以及信號(hao)(hao)的(de)幅(fu)度，其具(ju)體的(de)設計(ji)方案如(ru)下(xia)：
1、總體方案設計
信(xin)(xin)號(hao)(hao)發(fa)生(sheng)(sheng)器(qi)(qi)發(fa)送出(chu)去的(de)(de)是模擬(ni)信(xin)(xin)號(hao)(hao)，而(er)單(dan)片(pian)(pian)機輸(shu)(shu)出(chu)的(de)(de)是數(shu)字信(xin)(xin)號(hao)(hao)，因此在設計信(xin)(xin)號(hao)(hao)發(fa)生(sheng)(sheng)器(qi)(qi)系統時(shi)，需要使用到數(shu)模轉(zhuan)換芯片(pian)(pian)，可(ke)選擇(ze)數(shu)模轉(zhuan)換芯片(pian)(pian)DAC0832，然后再(zai)利用運算放(fang)大器(qi)(qi)將DAC0832輸(shu)(shu)出(chu)的(de)(de)電(dian)流信(xin)(xin)號(hao)(hao)轉(zhuan)換成電(dian)壓(ya)(ya)信(xin)(xin)號(hao)(hao)。這樣信(xin)(xin)號(hao)(hao)發(fa)生(sheng)(sheng)器(qi)(qi)便輸(shu)(shu)出(chu)了(le)模擬(ni)電(dian)壓(ya)(ya)。系統要輸(shu)(shu)出(chu)各(ge)種波形(xing)信(xin)(xin)號(hao)(hao)，則(ze)要求DAC0832在運放(fang)的(de)(de)作用下，在不(bu)同時(shi)間(jian)點輸(shu)(shu)出(chu)不(bu)同的(de)(de)電(dian)壓(ya)(ya)值(zhi)(zhi)，再(zai)將這些(xie)電(dian)壓(ya)(ya)值(zhi)(zhi)連接起來，便構成了(le)相應的(de)(de)波形(xing)信(xin)(xin)號(hao)(hao)。而(er)要得(de)到不(bu)同的(de)(de)電(dian)壓(ya)(ya)值(zhi)(zhi)，則(ze)單(dan)片(pian)(pian)機需要將8位I/O口(kou)(kou)接到DAC0832芯片(pian)(pian)的(de)(de)8位數(shu)據信(xin)(xin)號(hao)(hao)輸(shu)(shu)入(ru)端，單(dan)片(pian)(pian)機通(tong)過改變(bian)8位I/O口(kou)(kou)的(de)(de)數(shu)字信(xin)(xin)號(hao)(hao)，便可(ke)以在DAC0832以及運放(fang)的(de)(de)作用下，得(de)到不(bu)同的(de)(de)電(dian)壓(ya)(ya)值(zhi)(zhi)，再(zai)在時(shi)間(jian)的(de)(de)作用下形(xing)成不(bu)同的(de)(de)波形(xing)信(xin)(xin)號(hao)(hao)。波形(xing)信(xin)(xin)號(hao)(hao)頻率的(de)(de)的(de)(de)變(bian)化(hua)可(ke)通(tong)過改變(bian)單(dan)片(pian)(pian)機8位I/O輸(shu)(shu)出(chu)口(kou)(kou)的(de)(de)數(shu)據變(bian)化(hua)率來實現。
波形信(xin)號的幅度(du)由DAC0832的參(can)考(kao)電(dian)(dian)(dian)壓(ya)VREF來決(jue)定，為(wei)了(le)確(que)保VREF的大小可(ke)(ke)變，本系統使用(yong)到了(le)芯片(pian)(pian)(pian)PCF8591，將PCF8591芯片(pian)(pian)(pian)的模(mo)(mo)(mo)擬電(dian)(dian)(dian)壓(ya)輸出(chu)端接在(zai)DAC0832的VREF上，通(tong)(tong)過(guo)改(gai)變PCF8591模(mo)(mo)(mo)擬電(dian)(dian)(dian)壓(ya)輸出(chu)值(zhi)便可(ke)(ke)改(gai)變VREF值(zhi)，從而改(gai)變波形信(xin)號的幅度(du)值(zhi)。而PCF8591的模(mo)(mo)(mo)擬電(dian)(dian)(dian)壓(ya)輸出(chu)值(zhi)則(ze)是尤其I2C總行上的數據所決(jue)定，利用(yong)單(dan)片(pian)(pian)(pian)機(ji)的I/O口模(mo)(mo)(mo)擬I2C與PCF8591進行通(tong)(tong)信(xin)，那(nei)么單(dan)片(pian)(pian)(pian)機(ji)便可(ke)(ke)通(tong)(tong)過(guo)I/O口控(kong)制VREF電(dian)(dian)(dian)壓(ya)的變化(hua)，從而控(kong)制波形的幅度(du)變化(hua)。
2、系統硬件設計
（1）晶振電路設計
單片機(ji)穩定(ding)工作則(ze)需要穩定(ding)的(de)時鐘(zhong)信號，而(er)時鐘(zhong)信號則(ze)是(shi)由晶振(zhen)(zhen)電(dian)路產(chan)生(sheng)，因此晶振(zhen)(zhen)電(dian)路設(she)計的(de)好壞直接(jie)影響到最小系統的(de)穩定(ding)性。單片機(ji)的(de)18腳和19腳為晶振(zhen)(zhen)連接(jie)輸入腳，將晶振(zhen)(zhen)X1的(de)兩端(duan)連接(jie)到單片機(ji)18和19腳之后(hou)便會產(chan)生(sheng)時鐘(zhong)信號，此時的(de)信號會存(cun)在不(bu)穩定(ding)的(de)問(wen)題，需要在晶振(zhen)(zhen)Y1的(de)兩端(duan)分別外接(jie)一個22PF電(dian)容C1、C2到GND，該電(dian)容為晶振(zhen)(zhen)的(de)匹配(pei)電(dian)容，晶振(zhen)(zhen)匹配(pei)了電(dian)容之后(hou)，那么產(chan)生(sheng)的(de)時鐘(zhong)信號就比較穩定(ding)。出(chu)現的(de)頻偏也是(shi)在20PPM的(de)范圍內。這(zhe)樣才能確保系統時鐘(zhong)穩定(ding)可靠。
（2）復位電路設計
最小系(xi)(xi)統(tong)除了晶(jing)振電(dian)(dian)(dian)路(lu)之外，還需要(yao)具備復位電(dian)(dian)(dian)路(lu)，單片(pian)機上電(dian)(dian)(dian)后(hou)，啟動的時(shi)候，需要(yao)復位電(dian)(dian)(dian)路(lu)先進行復位，確保系(xi)(xi)統(tong)運行的起始(shi)地址一(yi)致 ，保證系(xi)(xi)統(tong)工作的穩定(ding)性(xing)，復位是利用電(dian)(dian)(dian)容(rong)C3與R1來實現的。
（3）波形幅度調節電路設計
為改變(bian)系統(tong)(tong)輸出(chu)的(de)(de)(de)波形幅度(du)值，本系統(tong)(tong)使用到了PCF8591芯片(pian)，該芯片(pian)是(shi)一個8位CMOS數(shu)據采集器，該芯片(pian)可(ke)以(yi)將模擬(ni)(ni)信(xin)號(hao)(hao)(hao)轉換成數(shu)字信(xin)號(hao)(hao)(hao)，再通過(guo)I2C數(shu)據總(zong)線(xian)將該數(shu)字信(xin)號(hao)(hao)(hao)發(fa)送給單(dan)片(pian)機；也可(ke)以(yi)反過(guo)來，單(dan)片(pian)機通過(guo)I2C總(zong)線(xian)將數(shu)字信(xin)號(hao)(hao)(hao)發(fa)送給PCF8591芯片(pian)，再由該芯片(pian)進行(xing)數(shu)模轉換后，變(bian)成模擬(ni)(ni)電壓(ya)再由AOUT腳輸出(chu)。利用這一原理，本系統(tong)(tong)為了調(diao)節信(xin)號(hao)(hao)(hao)發(fa)生器的(de)(de)(de)幅度(du)值，將單(dan)片(pian)機P2.0和P2.1模擬(ni)(ni)I2C與PCF8591通信(xin)，這樣單(dan)片(pian)機便可(ke)以(yi)控(kong)制(zhi)PCF8591的(de)(de)(de)AOUT輸出(chu)端(duan)模擬(ni)(ni)電壓(ya)的(de)(de)(de)大小，再將其接入到DAC0832的(de)(de)(de)VREF腳上(shang)，便可(ke)以(yi)控(kong)制(zhi)波形的(de)(de)(de)幅度(du)。
（4）數模轉換電路設計
信號發生(sheng)器(qi)產生(sheng)各(ge)種波形(xing)信號使(shi)(shi)用到了DAC0832數(shu)模(mo)轉(zhuan)換(huan)芯片，該芯片內(nei)部(bu)集成了一個(ge)(ge)8位D/A轉(zhuan)換(huan)器(qi)，一個(ge)(ge)8為DAC寄存器(qi)，一個(ge)(ge)8位輸入寄存器(qi)以(yi)及一個(ge)(ge)控制電(dian)路(lu)，其內(nei)部(bu)采用的是倒(dao)T型(xing)R-2R電(dian)阻網絡，將該數(shu)模(mo)轉(zhuan)換(huan)芯片與運(yun)算放大器(qi)LM358一起(qi)使(shi)(shi)用，便(bian)可以(yi)使(shi)(shi)運(yun)放輸出(chu)端有28 =256個(ge)(ge)電(dian)壓值輸出(chu)。在不同時間內(nei)變(bian)換(huan)輸出(chu)不同的電(dian)壓值，使(shi)(shi)其產生(sheng)周期性的變(bian)化便(bian)能(neng)形(xing)成相應的波形(xing)信號。
（5）按鍵中斷控制電路設計
基于(yu)單(dan)片機(ji)的(de)信(xin)(xin)號發(fa)生(sheng)器(qi)(qi)要求輸(shu)出方波、三(san)角波、鋸齒(chi)波以及正(zheng)弦波信(xin)(xin)號，信(xin)(xin)號的(de)幅度(du)和頻(pin)率(lv)可(ke)調(diao)(diao)，用戶(hu)可(ke)通過系統按(an)(an)(an)(an)鍵(jian)(jian)(jian)來(lai)對(dui)信(xin)(xin)號發(fa)生(sheng)器(qi)(qi)進行設(she)置。在系統中，設(she)計(ji)了8個按(an)(an)(an)(an)鍵(jian)(jian)(jian)，其功能分別為(wei)100HZ頻(pin)率(lv)加(jia)按(an)(an)(an)(an)鍵(jian)(jian)(jian)、1hz頻(pin)率(lv)加(jia)按(an)(an)(an)(an)鍵(jian)(jian)(jian)、-1hz頻(pin)率(lv)減按(an)(an)(an)(an)鍵(jian)(jian)(jian)、1V電壓(ya)幅度(du)加(jia)按(an)(an)(an)(an)鍵(jian)(jian)(jian)、0.1V電壓(ya)幅度(du)加(jia)按(an)(an)(an)(an)鍵(jian)(jian)(jian)、-0.1V電壓(ya)幅度(du)減按(an)(an)(an)(an)鍵(jian)(jian)(jian)、波形切換按(an)(an)(an)(an)鍵(jian)(jian)(jian)、掃頻(pin)開關按(an)(an)(an)(an)鍵(jian)(jian)(jian)。為(wei)了方便系統設(she)計(ji)，采用獨(du)立(li)按(an)(an)(an)(an)鍵(jian)(jian)(jian)設(she)計(ji)方法，利用單(dan)片機(ji)P1口(kou)將(jiang)各(ge)按(an)(an)(an)(an)鍵(jian)(jian)(jian)連接，通過軟件將(jiang)P1口(kou)設(she)置成上拉(la)狀(zhuang)態。當沒有(you)按(an)(an)(an)(an)鍵(jian)(jian)(jian)按(an)(an)(an)(an)下時，單(dan)片機(ji)P1口(kou)中的(de)所有(you)I/O口(kou)檢測(ce)的(de)到時高(gao)電平；當有(you)按(an)(an)(an)(an)鍵(jian)(jian)(jian)按(an)(an)(an)(an)下時，則該按(an)(an)(an)(an)鍵(jian)(jian)(jian)對(dui)應(ying)單(dan)片機(ji)的(de)I/O口(kou)會被拉(la)低，變成低電平。單(dan)片機(ji)便能檢測(ce)到，從而(er)調(diao)(diao)用該按(an)(an)(an)(an)鍵(jian)(jian)(jian)程序執行相應(ying)的(de)功能。
（6）電源電路設計
本系(xi)統(tong)電(dian)(dian)路設(she)計是(shi)在Proteus仿真(zhen)(zhen)軟(ruan)件(jian)(jian)上(shang)設(she)計，該仿真(zhen)(zhen)軟(ruan)件(jian)(jian)有(you)各種電(dian)(dian)源，可直(zhi)(zhi)接調用。無需使(shi)用電(dian)(dian)壓(ya)轉換芯片。在本系(xi)統(tong)單片機(ji)使(shi)用5V電(dian)(dian)壓(ya)供(gong)電(dian)(dian)，而為了(le)使(shi)輸出波(bo)形幅(fu)度為10V，則PCF8591采用10V電(dian)(dian)壓(ya)供(gong)電(dian)(dian)，而運算放大器采用±15V供(gong)電(dian)(dian)，直(zhi)(zhi)接從仿真(zhen)(zhen)軟(ruan)件(jian)(jian)上(shang)取(qu)電(dian)(dian)源即可。
3、系統軟件設計
完成(cheng)proteus軟(ruan)件電路圖設計之后，接下來(lai)需要對單片機編(bian)寫(xie)(xie)驅(qu)(qu)動程序(xu)，系統驅(qu)(qu)動程序(xu)的編(bian)寫(xie)(xie)是(shi)在keil軟(ruan)件平臺上完成(cheng)的，Keil軟(ruan)件打開后，要先建(jian)立工程，然后在工程當中(zhong)建(jian)立一(yi)個.c文件，在此(ci)文件中(zhong)編(bian)寫(xie)(xie)代碼驅(qu)(qu)動程序(xu)：
（1）系統主程序設計
主程(cheng)(cheng)序(xu)是軟件系(xi)統(tong)中最(zui)為重要的(de)(de)(de)(de)程(cheng)(cheng)序(xu)，因為系(xi)統(tong)程(cheng)(cheng)序(xu)是由各個子程(cheng)(cheng)序(xu)所構成，而(er)子程(cheng)(cheng)序(xu)的(de)(de)(de)(de)調用全部是在(zai)主程(cheng)(cheng)序(xu)中來(lai)實現的(de)(de)(de)(de)，主程(cheng)(cheng)序(xu)設計的(de)(de)(de)(de)好(hao)壞直接能影響到系(xi)統(tong)的(de)(de)(de)(de)邏(luo)輯結(jie)構，影響到系(xi)統(tong)工作的(de)(de)(de)(de)穩定性。在(zai)本系(xi)統(tong)中，系(xi)統(tong)開始(shi)運(yun)行(xing)后(hou)，先會執行(xing)主程(cheng)(cheng)序(xu)，在(zai)主程(cheng)(cheng)序(xu)中對單片機及其外圍元件進行(xing)初始(shi)化設置，完成初始(shi)化設置之后(hou)，系(xi)統(tong)就(jiu)會執行(xing)正(zheng)弦波(bo)(bo)(bo)程(cheng)(cheng)序(xu)，讓(rang)信號發生(sheng)器(qi)輸出正(zheng)弦波(bo)(bo)(bo)信號，然后(hou)再(zai)去(qu)檢(jian)測是否有按(an)(an)鍵(jian)(jian)(jian)按(an)(an)下，如(ru)果有按(an)(an)鍵(jian)(jian)(jian)按(an)(an)下，系(xi)統(tong)檢(jian)測到后(hou)，便(bian)會執行(xing)相應按(an)(an)鍵(jian)(jian)(jian)的(de)(de)(de)(de)程(cheng)(cheng)序(xu)，從而(er)改變信號發生(sheng)器(qi)輸出的(de)(de)(de)(de)波(bo)(bo)(bo)形。如(ru)果沒有按(an)(an)鍵(jian)(jian)(jian)產(chan)生(sheng)，則系(xi)統(tong)繼(ji)續保持當前波(bo)(bo)(bo)形輸出，然后(hou)再(zai)繼(ji)續去(qu)訪問是否有按(an)(an)鍵(jian)(jian)(jian)按(an)(an)下，如(ru)此循(xun)環下去(qu)。
（2）按鍵掃描程序設計
本系統(tong)是通(tong)過按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)來改變信號發生器的波(bo)(bo)形(xing)，系統(tong)一共有八(ba)個按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)，按(an)(an)(an)(an)(an)下不(bu)同按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)時(shi)，系統(tong)需要輸(shu)(shu)(shu)出(chu)(chu)(chu)不(bu)同的波(bo)(bo)形(xing)。定(ding)義(yi)按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)6為(wei)(wei)(wei)波(bo)(bo)形(xing)切(qie)換按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)，按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)0為(wei)(wei)(wei)100HZ頻率(lv)增(zeng)(zeng)加按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)，按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)1為(wei)(wei)(wei)1HZ頻率(lv)增(zeng)(zeng)加按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)，按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)2為(wei)(wei)(wei)1HZ頻率(lv)減按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)，按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)3位1V幅(fu)(fu)度(du)(du)增(zeng)(zeng)加按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)，按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)4為(wei)(wei)(wei)0.1V幅(fu)(fu)度(du)(du)增(zeng)(zeng)加按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)，按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)5為(wei)(wei)(wei)0.1V幅(fu)(fu)度(du)(du)減小按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)，按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)7位掃頻按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)，flang為(wei)(wei)(wei)標志位，用于判斷按(an)(an)(an)(an)(an)鍵(jian)(jian)(jian)6按(an)(an)(an)(an)(an)下的次數(shu)當(dang)flang為(wei)(wei)(wei)1是默(mo)認輸(shu)(shu)(shu)出(chu)(chu)(chu)正弦(xian)波(bo)(bo)；當(dang)flang為(wei)(wei)(wei)2時(shi)，輸(shu)(shu)(shu)出(chu)(chu)(chu)三(san)角波(bo)(bo)；當(dang)flang為(wei)(wei)(wei)3時(shi)輸(shu)(shu)(shu)出(chu)(chu)(chu)鋸齒波(bo)(bo)；當(dang)flang為(wei)(wei)(wei)4時(shi)，輸(shu)(shu)(shu)出(chu)(chu)(chu)方波(bo)(bo)；當(dang)flang為(wei)(wei)(wei)5時(shi)，則會(hui)令flang=1，輸(shu)(shu)(shu)出(chu)(chu)(chu)正弦(xian)波(bo)(bo)。
因此，當(dang)(dang)(dang)有按(an)(an)鍵(jian)(jian)(jian)(jian)按(an)(an)下(xia)(xia)(xia)時，系(xi)統調用按(an)(an)鍵(jian)(jian)(jian)(jian)程序會去(qu)判斷是哪個按(an)(an)鍵(jian)(jian)(jian)(jian)按(an)(an)下(xia)(xia)(xia)，如果是按(an)(an)鍵(jian)(jian)(jian)(jian)6按(an)(an)下(xia)(xia)(xia)，表示(shi)需要切(qie)換信號(hao)發生器的(de)輸出(chu)波(bo)形(xing)，令flang+1，然后判斷flang的(de)值，再輸出(chu)相應的(de)波(bo)形(xing)信號(hao)。當(dang)(dang)(dang)是0按(an)(an)鍵(jian)(jian)(jian)(jian)按(an)(an)下(xia)(xia)(xia)時，則(ze)(ze)系(xi)統會在(zai)原有的(de)波(bo)形(xing)上，改變其輸出(chu)頻率(lv)(lv)，使頻率(lv)(lv)增加(jia)100HZ；當(dang)(dang)(dang)按(an)(an)下(xia)(xia)(xia)的(de)是1按(an)(an)鍵(jian)(jian)(jian)(jian)，則(ze)(ze)將(jiang)頻率(lv)(lv)增加(jia)1HZ；當(dang)(dang)(dang)2按(an)(an)鍵(jian)(jian)(jian)(jian)按(an)(an)下(xia)(xia)(xia)，則(ze)(ze)將(jiang)頻率(lv)(lv)減(jian)小(xiao)1HZ；當(dang)(dang)(dang)按(an)(an)鍵(jian)(jian)(jian)(jian)3按(an)(an)下(xia)(xia)(xia)時，表示(shi)要在(zai)原有波(bo)形(xing)的(de)基礎上增加(jia)1V的(de)波(bo)形(xing)幅度(du)；當(dang)(dang)(dang)4按(an)(an)鍵(jian)(jian)(jian)(jian)按(an)(an)下(xia)(xia)(xia)，則(ze)(ze)幅度(du)增加(jia)0.1V；當(dang)(dang)(dang)5按(an)(an)鍵(jian)(jian)(jian)(jian)按(an)(an)下(xia)(xia)(xia)，則(ze)(ze)幅度(du)減(jian)小(xiao)0.1V；當(dang)(dang)(dang)7按(an)(an)鍵(jian)(jian)(jian)(jian)按(an)(an)下(xia)(xia)(xia)，則(ze)(ze)進(jin)行掃(sao)頻。當(dang)(dang)(dang)執(zhi)行完按(an)(an)鍵(jian)(jian)(jian)(jian)程序后，返回(hui)系(xi)統主程序。
二、信號發生器的設計要求有哪些
基于單片機設計的信號發生器屬于簡易信號發生器，主要能產生方波、三角波和正弦波并進行仿真，這類信號發生器設計好(hao)后，應滿(man)足(zu)以下要求：
1、基本性能指標要求
（1）頻(pin)率范圍：100Hz~1kHz。
（2）輸出電壓：方波 Up-p≤24V，三角波 Up-p=6V，正弦波 Up-p>1V。
2、擴展性能指標要求
頻率(lv)范圍分(fen)段設置10Hz~100Hz，100Hz~1kHz，1kHz~10kHz；波(bo)(bo)(bo)形特性方波(bo)(bo)(bo)t r<30us（1kHz，最(zui)大輸(shu)出時），三角波(bo)(bo)(bo)r△<2%，正(zheng)弦(xian)波(bo)(bo)(bo)r～<5%。
