一、基于單片機的信號發生器設計方案
信(xin)號(hao)發生(sheng)器用于調(diao)節(jie)射頻(pin)匹配電路，可以自行設計，一般普通(tong)的信(xin)號(hao)發生(sheng)器需要(yao)輸出(chu)正弦(xian)波(bo)、方波(bo)、三角波(bo)以及(ji)鋸齒波(bo)等信(xin)號(hao)，可通(tong)過按鍵調(diao)節(jie)信(xin)號(hao)的頻(pin)率以及(ji)信(xin)號(hao)的幅(fu)度，其具體的設計方案如下：
1、總體方案設計
信(xin)號(hao)(hao)(hao)(hao)(hao)發(fa)(fa)生器(qi)發(fa)(fa)送出去的(de)(de)是(shi)(shi)模(mo)擬(ni)信(xin)號(hao)(hao)(hao)(hao)(hao)，而(er)單(dan)片(pian)機輸(shu)出的(de)(de)是(shi)(shi)數(shu)字信(xin)號(hao)(hao)(hao)(hao)(hao)，因(yin)此(ci)在(zai)設計信(xin)號(hao)(hao)(hao)(hao)(hao)發(fa)(fa)生器(qi)系統時(shi)，需要(yao)使用到(dao)數(shu)模(mo)轉換(huan)芯(xin)片(pian)，可選(xuan)擇(ze)數(shu)模(mo)轉換(huan)芯(xin)片(pian)DAC0832，然(ran)后再利(li)用運(yun)算放(fang)大器(qi)將DAC0832輸(shu)出的(de)(de)電(dian)(dian)流(liu)信(xin)號(hao)(hao)(hao)(hao)(hao)轉換(huan)成電(dian)(dian)壓(ya)信(xin)號(hao)(hao)(hao)(hao)(hao)。這樣信(xin)號(hao)(hao)(hao)(hao)(hao)發(fa)(fa)生器(qi)便輸(shu)出了模(mo)擬(ni)電(dian)(dian)壓(ya)。系統要(yao)輸(shu)出各種波(bo)形(xing)信(xin)號(hao)(hao)(hao)(hao)(hao)，則(ze)要(yao)求DAC0832在(zai)運(yun)放(fang)的(de)(de)作用下(xia)，在(zai)不(bu)同時(shi)間(jian)點輸(shu)出不(bu)同的(de)(de)電(dian)(dian)壓(ya)值，再將這些電(dian)(dian)壓(ya)值連接(jie)起來，便構成了相應(ying)的(de)(de)波(bo)形(xing)信(xin)號(hao)(hao)(hao)(hao)(hao)。而(er)要(yao)得到(dao)不(bu)同的(de)(de)電(dian)(dian)壓(ya)值，則(ze)單(dan)片(pian)機需要(yao)將8位(wei)I/O口接(jie)到(dao)DAC0832芯(xin)片(pian)的(de)(de)8位(wei)數(shu)據(ju)(ju)信(xin)號(hao)(hao)(hao)(hao)(hao)輸(shu)入端，單(dan)片(pian)機通過改(gai)變8位(wei)I/O口的(de)(de)數(shu)字信(xin)號(hao)(hao)(hao)(hao)(hao)，便可以(yi)在(zai)DAC0832以(yi)及運(yun)放(fang)的(de)(de)作用下(xia)，得到(dao)不(bu)同的(de)(de)電(dian)(dian)壓(ya)值，再在(zai)時(shi)間(jian)的(de)(de)作用下(xia)形(xing)成不(bu)同的(de)(de)波(bo)形(xing)信(xin)號(hao)(hao)(hao)(hao)(hao)。波(bo)形(xing)信(xin)號(hao)(hao)(hao)(hao)(hao)頻率(lv)的(de)(de)的(de)(de)變化可通過改(gai)變單(dan)片(pian)機8位(wei)I/O輸(shu)出口的(de)(de)數(shu)據(ju)(ju)變化率(lv)來實(shi)現。
波(bo)(bo)形信(xin)號的(de)(de)幅度由DAC0832的(de)(de)參考(kao)電壓(ya)(ya)VREF來決(jue)定(ding)，為了確保VREF的(de)(de)大(da)小可變(bian)(bian)，本系統使用到了芯(xin)片PCF8591，將PCF8591芯(xin)片的(de)(de)模(mo)擬電壓(ya)(ya)輸(shu)(shu)出端接在DAC0832的(de)(de)VREF上，通過(guo)改(gai)(gai)變(bian)(bian)PCF8591模(mo)擬電壓(ya)(ya)輸(shu)(shu)出值便可改(gai)(gai)變(bian)(bian)VREF值，從而改(gai)(gai)變(bian)(bian)波(bo)(bo)形信(xin)號的(de)(de)幅度值。而PCF8591的(de)(de)模(mo)擬電壓(ya)(ya)輸(shu)(shu)出值則是(shi)尤其I2C總(zong)行上的(de)(de)數據所(suo)決(jue)定(ding)，利用單片機(ji)的(de)(de)I/O口模(mo)擬I2C與PCF8591進行通信(xin)，那(nei)么單片機(ji)便可通過(guo)I/O口控制(zhi)VREF電壓(ya)(ya)的(de)(de)變(bian)(bian)化，從而控制(zhi)波(bo)(bo)形的(de)(de)幅度變(bian)(bian)化。
2、系統硬件設計
（1）晶振電路設計
單(dan)片機(ji)穩(wen)定工作則需要穩(wen)定的(de)時(shi)鐘(zhong)(zhong)(zhong)信(xin)號，而時(shi)鐘(zhong)(zhong)(zhong)信(xin)號則是由晶(jing)振電(dian)路產生(sheng)，因此晶(jing)振電(dian)路設計的(de)好壞直接(jie)影響(xiang)到(dao)最小(xiao)系(xi)統(tong)的(de)穩(wen)定性。單(dan)片機(ji)的(de)18腳和(he)19腳為晶(jing)振連接(jie)輸入(ru)腳，將晶(jing)振X1的(de)兩端(duan)連接(jie)到(dao)單(dan)片機(ji)18和(he)19腳之后便會產生(sheng)時(shi)鐘(zhong)(zhong)(zhong)信(xin)號，此時(shi)的(de)信(xin)號會存(cun)在不穩(wen)定的(de)問題，需要在晶(jing)振Y1的(de)兩端(duan)分別外接(jie)一(yi)個22PF電(dian)容C1、C2到(dao)GND，該電(dian)容為晶(jing)振的(de)匹配電(dian)容，晶(jing)振匹配了電(dian)容之后，那么產生(sheng)的(de)時(shi)鐘(zhong)(zhong)(zhong)信(xin)號就(jiu)比(bi)較穩(wen)定。出現(xian)的(de)頻偏也(ye)是在20PPM的(de)范圍內。這(zhe)樣(yang)才能(neng)確保(bao)系(xi)統(tong)時(shi)鐘(zhong)(zhong)(zhong)穩(wen)定可靠。
（2）復位電路設計
最小(xiao)系(xi)統(tong)(tong)除了晶振電(dian)(dian)路之(zhi)外，還需要具備復位(wei)電(dian)(dian)路，單片機上電(dian)(dian)后，啟動的時候，需要復位(wei)電(dian)(dian)路先進行(xing)復位(wei)，確保系(xi)統(tong)(tong)運行(xing)的起始(shi)地址(zhi)一致 ，保證系(xi)統(tong)(tong)工(gong)作的穩定(ding)性，復位(wei)是利用電(dian)(dian)容C3與R1來實現(xian)的。
（3）波形幅度調節電路設計
為改變(bian)系統(tong)輸出的(de)波(bo)形幅(fu)(fu)度值(zhi)，本系統(tong)使用(yong)到了(le)PCF8591芯(xin)(xin)(xin)片(pian)(pian)(pian)，該芯(xin)(xin)(xin)片(pian)(pian)(pian)是一(yi)個8位CMOS數據采集(ji)器，該芯(xin)(xin)(xin)片(pian)(pian)(pian)可(ke)以(yi)將模(mo)擬信(xin)(xin)號(hao)(hao)(hao)(hao)轉換(huan)成數字(zi)信(xin)(xin)號(hao)(hao)(hao)(hao)，再通(tong)過(guo)(guo)I2C數據總線將該數字(zi)信(xin)(xin)號(hao)(hao)(hao)(hao)發(fa)送給單(dan)片(pian)(pian)(pian)機；也可(ke)以(yi)反過(guo)(guo)來(lai)，單(dan)片(pian)(pian)(pian)機通(tong)過(guo)(guo)I2C總線將數字(zi)信(xin)(xin)號(hao)(hao)(hao)(hao)發(fa)送給PCF8591芯(xin)(xin)(xin)片(pian)(pian)(pian)，再由(you)該芯(xin)(xin)(xin)片(pian)(pian)(pian)進行(xing)數模(mo)轉換(huan)后，變(bian)成模(mo)擬電(dian)壓再由(you)AOUT腳輸出。利用(yong)這(zhe)一(yi)原(yuan)理(li)，本系統(tong)為了(le)調節信(xin)(xin)號(hao)(hao)(hao)(hao)發(fa)生器的(de)幅(fu)(fu)度值(zhi)，將單(dan)片(pian)(pian)(pian)機P2.0和P2.1模(mo)擬I2C與PCF8591通(tong)信(xin)(xin)，這(zhe)樣單(dan)片(pian)(pian)(pian)機便可(ke)以(yi)控制(zhi)PCF8591的(de)AOUT輸出端模(mo)擬電(dian)壓的(de)大小，再將其接入到DAC0832的(de)VREF腳上，便可(ke)以(yi)控制(zhi)波(bo)形的(de)幅(fu)(fu)度。
（4）數模轉換電路設計
信號(hao)發生(sheng)器產(chan)生(sheng)各種波(bo)形(xing)信號(hao)使用到了DAC0832數模轉(zhuan)換(huan)(huan)芯(xin)片，該(gai)(gai)芯(xin)片內(nei)(nei)(nei)部集成(cheng)了一(yi)個8位D/A轉(zhuan)換(huan)(huan)器，一(yi)個8為DAC寄存器，一(yi)個8位輸(shu)(shu)入寄存器以及(ji)一(yi)個控制(zhi)電(dian)(dian)路，其內(nei)(nei)(nei)部采用的(de)(de)是倒T型R-2R電(dian)(dian)阻網絡，將該(gai)(gai)數模轉(zhuan)換(huan)(huan)芯(xin)片與運算放(fang)大器LM358一(yi)起使用，便(bian)可以使運放(fang)輸(shu)(shu)出端有28 =256個電(dian)(dian)壓(ya)值輸(shu)(shu)出。在(zai)不(bu)同時間內(nei)(nei)(nei)變換(huan)(huan)輸(shu)(shu)出不(bu)同的(de)(de)電(dian)(dian)壓(ya)值，使其產(chan)生(sheng)周期性的(de)(de)變化便(bian)能(neng)形(xing)成(cheng)相應的(de)(de)波(bo)形(xing)信號(hao)。
（5）按鍵中斷控制電路設計
基于(yu)單片(pian)(pian)(pian)(pian)機(ji)(ji)的(de)信(xin)號(hao)(hao)(hao)發(fa)生器(qi)要(yao)求(qiu)輸出方(fang)(fang)波、三角波、鋸齒波以及正弦波信(xin)號(hao)(hao)(hao)，信(xin)號(hao)(hao)(hao)的(de)幅(fu)(fu)度(du)和頻(pin)率可(ke)調，用戶可(ke)通(tong)過系統按(an)(an)(an)鍵(jian)(jian)(jian)(jian)來對信(xin)號(hao)(hao)(hao)發(fa)生器(qi)進行設置(zhi)。在(zai)系統中(zhong)，設計了8個按(an)(an)(an)鍵(jian)(jian)(jian)(jian)，其功能分別為100HZ頻(pin)率加按(an)(an)(an)鍵(jian)(jian)(jian)(jian)、1hz頻(pin)率加按(an)(an)(an)鍵(jian)(jian)(jian)(jian)、-1hz頻(pin)率減(jian)按(an)(an)(an)鍵(jian)(jian)(jian)(jian)、1V電(dian)(dian)壓(ya)幅(fu)(fu)度(du)加按(an)(an)(an)鍵(jian)(jian)(jian)(jian)、0.1V電(dian)(dian)壓(ya)幅(fu)(fu)度(du)加按(an)(an)(an)鍵(jian)(jian)(jian)(jian)、-0.1V電(dian)(dian)壓(ya)幅(fu)(fu)度(du)減(jian)按(an)(an)(an)鍵(jian)(jian)(jian)(jian)、波形切換按(an)(an)(an)鍵(jian)(jian)(jian)(jian)、掃頻(pin)開關按(an)(an)(an)鍵(jian)(jian)(jian)(jian)。為了方(fang)(fang)便(bian)系統設計，采用獨立按(an)(an)(an)鍵(jian)(jian)(jian)(jian)設計方(fang)(fang)法，利用單片(pian)(pian)(pian)(pian)機(ji)(ji)P1口(kou)將(jiang)各按(an)(an)(an)鍵(jian)(jian)(jian)(jian)連接，通(tong)過軟件將(jiang)P1口(kou)設置(zhi)成(cheng)上(shang)拉狀態。當沒有(you)按(an)(an)(an)鍵(jian)(jian)(jian)(jian)按(an)(an)(an)下(xia)(xia)時，單片(pian)(pian)(pian)(pian)機(ji)(ji)P1口(kou)中(zhong)的(de)所有(you)I/O口(kou)檢測(ce)的(de)到時高電(dian)(dian)平；當有(you)按(an)(an)(an)鍵(jian)(jian)(jian)(jian)按(an)(an)(an)下(xia)(xia)時，則該(gai)按(an)(an)(an)鍵(jian)(jian)(jian)(jian)對應單片(pian)(pian)(pian)(pian)機(ji)(ji)的(de)I/O口(kou)會被拉低，變成(cheng)低電(dian)(dian)平。單片(pian)(pian)(pian)(pian)機(ji)(ji)便(bian)能檢測(ce)到，從而(er)調用該(gai)按(an)(an)(an)鍵(jian)(jian)(jian)(jian)程序執(zhi)行相應的(de)功能。
（6）電源電路設計
本(ben)系(xi)統(tong)電(dian)路(lu)設計是在Proteus仿真(zhen)軟(ruan)件上設計，該仿真(zhen)軟(ruan)件有各(ge)種電(dian)源，可直接調用(yong)(yong)。無需使用(yong)(yong)電(dian)壓(ya)轉換芯片(pian)。在本(ben)系(xi)統(tong)單(dan)片(pian)機使用(yong)(yong)5V電(dian)壓(ya)供電(dian)，而為了使輸出波(bo)形(xing)幅(fu)度為10V，則PCF8591采用(yong)(yong)10V電(dian)壓(ya)供電(dian)，而運算放(fang)大器采用(yong)(yong)±15V供電(dian)，直接從仿真(zhen)軟(ruan)件上取電(dian)源即(ji)可。
3、系統軟件設計
完成(cheng)proteus軟件(jian)(jian)(jian)(jian)電路圖設(she)計之后，接下來需要(yao)對單片機編寫驅(qu)(qu)動程序，系統(tong)驅(qu)(qu)動程序的編寫是在(zai)keil軟件(jian)(jian)(jian)(jian)平(ping)臺上完成(cheng)的，Keil軟件(jian)(jian)(jian)(jian)打開后，要(yao)先建立(li)工(gong)程，然后在(zai)工(gong)程當(dang)中(zhong)建立(li)一個.c文(wen)(wen)件(jian)(jian)(jian)(jian)，在(zai)此(ci)文(wen)(wen)件(jian)(jian)(jian)(jian)中(zhong)編寫代碼驅(qu)(qu)動程序：
（1）系統主程序設計
主程(cheng)(cheng)(cheng)序(xu)(xu)是(shi)軟件系統(tong)(tong)(tong)(tong)中(zhong)最為重要的(de)(de)(de)程(cheng)(cheng)(cheng)序(xu)(xu)，因為系統(tong)(tong)(tong)(tong)程(cheng)(cheng)(cheng)序(xu)(xu)是(shi)由(you)各個子程(cheng)(cheng)(cheng)序(xu)(xu)所(suo)構(gou)成，而子程(cheng)(cheng)(cheng)序(xu)(xu)的(de)(de)(de)調用全部是(shi)在(zai)主程(cheng)(cheng)(cheng)序(xu)(xu)中(zhong)來實現的(de)(de)(de)，主程(cheng)(cheng)(cheng)序(xu)(xu)設(she)計的(de)(de)(de)好壞直(zhi)接能(neng)影響(xiang)到(dao)系統(tong)(tong)(tong)(tong)的(de)(de)(de)邏輯結構(gou)，影響(xiang)到(dao)系統(tong)(tong)(tong)(tong)工作的(de)(de)(de)穩定性。在(zai)本系統(tong)(tong)(tong)(tong)中(zhong)，系統(tong)(tong)(tong)(tong)開始(shi)(shi)運行(xing)后，先會執(zhi)行(xing)主程(cheng)(cheng)(cheng)序(xu)(xu)，在(zai)主程(cheng)(cheng)(cheng)序(xu)(xu)中(zhong)對單片機及其外(wai)圍(wei)元件進行(xing)初始(shi)(shi)化設(she)置，完(wan)成初始(shi)(shi)化設(she)置之(zhi)后，系統(tong)(tong)(tong)(tong)就會執(zhi)行(xing)正弦波程(cheng)(cheng)(cheng)序(xu)(xu)，讓信(xin)號(hao)(hao)發生(sheng)器輸出正弦波信(xin)號(hao)(hao)，然后再去(qu)檢測是(shi)否(fou)有(you)按(an)(an)(an)鍵按(an)(an)(an)下，如果有(you)按(an)(an)(an)鍵按(an)(an)(an)下，系統(tong)(tong)(tong)(tong)檢測到(dao)后，便(bian)會執(zhi)行(xing)相應按(an)(an)(an)鍵的(de)(de)(de)程(cheng)(cheng)(cheng)序(xu)(xu)，從而改變信(xin)號(hao)(hao)發生(sheng)器輸出的(de)(de)(de)波形。如果沒(mei)有(you)按(an)(an)(an)鍵產生(sheng)，則(ze)系統(tong)(tong)(tong)(tong)繼續(xu)保持當前(qian)波形輸出，然后再繼續(xu)去(qu)訪問是(shi)否(fou)有(you)按(an)(an)(an)鍵按(an)(an)(an)下，如此循環下去(qu)。
（2）按鍵掃描程序設計
本系(xi)統(tong)是(shi)通過(guo)按(an)(an)鍵(jian)(jian)(jian)來改變(bian)信號發生器(qi)的(de)(de)波(bo)(bo)形，系(xi)統(tong)一共有八個按(an)(an)鍵(jian)(jian)(jian)，按(an)(an)下不同按(an)(an)鍵(jian)(jian)(jian)時(shi)(shi)，系(xi)統(tong)需要輸(shu)出(chu)(chu)不同的(de)(de)波(bo)(bo)形。定義(yi)按(an)(an)鍵(jian)(jian)(jian)6為波(bo)(bo)形切換按(an)(an)鍵(jian)(jian)(jian)，按(an)(an)鍵(jian)(jian)(jian)0為100HZ頻(pin)率(lv)增(zeng)加按(an)(an)鍵(jian)(jian)(jian)，按(an)(an)鍵(jian)(jian)(jian)1為1HZ頻(pin)率(lv)增(zeng)加按(an)(an)鍵(jian)(jian)(jian)，按(an)(an)鍵(jian)(jian)(jian)2為1HZ頻(pin)率(lv)減(jian)按(an)(an)鍵(jian)(jian)(jian)，按(an)(an)鍵(jian)(jian)(jian)3位(wei)1V幅度增(zeng)加按(an)(an)鍵(jian)(jian)(jian)，按(an)(an)鍵(jian)(jian)(jian)4為0.1V幅度增(zeng)加按(an)(an)鍵(jian)(jian)(jian)，按(an)(an)鍵(jian)(jian)(jian)5為0.1V幅度減(jian)小按(an)(an)鍵(jian)(jian)(jian)，按(an)(an)鍵(jian)(jian)(jian)7位(wei)掃頻(pin)按(an)(an)鍵(jian)(jian)(jian)，flang為標志位(wei)，用于(yu)判斷按(an)(an)鍵(jian)(jian)(jian)6按(an)(an)下的(de)(de)次數當(dang)(dang)flang為1是(shi)默(mo)認輸(shu)出(chu)(chu)正弦波(bo)(bo)；當(dang)(dang)flang為2時(shi)(shi)，輸(shu)出(chu)(chu)三角波(bo)(bo)；當(dang)(dang)flang為3時(shi)(shi)輸(shu)出(chu)(chu)鋸齒波(bo)(bo)；當(dang)(dang)flang為4時(shi)(shi)，輸(shu)出(chu)(chu)方波(bo)(bo)；當(dang)(dang)flang為5時(shi)(shi)，則(ze)會令flang=1，輸(shu)出(chu)(chu)正弦波(bo)(bo)。
因此，當(dang)(dang)(dang)(dang)(dang)有(you)按(an)(an)(an)(an)(an)鍵(jian)(jian)按(an)(an)(an)(an)(an)下(xia)時，系(xi)統(tong)調用按(an)(an)(an)(an)(an)鍵(jian)(jian)程(cheng)序(xu)會(hui)(hui)去判(pan)斷是(shi)(shi)哪個按(an)(an)(an)(an)(an)鍵(jian)(jian)按(an)(an)(an)(an)(an)下(xia)，如果(guo)是(shi)(shi)按(an)(an)(an)(an)(an)鍵(jian)(jian)6按(an)(an)(an)(an)(an)下(xia)，表(biao)示需要切(qie)換(huan)信號(hao)發生器(qi)的輸出波(bo)形(xing)，令flang+1，然后(hou)判(pan)斷flang的值，再輸出相應的波(bo)形(xing)信號(hao)。當(dang)(dang)(dang)(dang)(dang)是(shi)(shi)0按(an)(an)(an)(an)(an)鍵(jian)(jian)按(an)(an)(an)(an)(an)下(xia)時，則(ze)(ze)系(xi)統(tong)會(hui)(hui)在原(yuan)有(you)的波(bo)形(xing)上，改變(bian)其輸出頻率，使頻率增加(jia)100HZ；當(dang)(dang)(dang)(dang)(dang)按(an)(an)(an)(an)(an)下(xia)的是(shi)(shi)1按(an)(an)(an)(an)(an)鍵(jian)(jian)，則(ze)(ze)將(jiang)頻率增加(jia)1HZ；當(dang)(dang)(dang)(dang)(dang)2按(an)(an)(an)(an)(an)鍵(jian)(jian)按(an)(an)(an)(an)(an)下(xia)，則(ze)(ze)將(jiang)頻率減(jian)小(xiao)1HZ；當(dang)(dang)(dang)(dang)(dang)按(an)(an)(an)(an)(an)鍵(jian)(jian)3按(an)(an)(an)(an)(an)下(xia)時，表(biao)示要在原(yuan)有(you)波(bo)形(xing)的基礎上增加(jia)1V的波(bo)形(xing)幅度(du)；當(dang)(dang)(dang)(dang)(dang)4按(an)(an)(an)(an)(an)鍵(jian)(jian)按(an)(an)(an)(an)(an)下(xia)，則(ze)(ze)幅度(du)增加(jia)0.1V；當(dang)(dang)(dang)(dang)(dang)5按(an)(an)(an)(an)(an)鍵(jian)(jian)按(an)(an)(an)(an)(an)下(xia)，則(ze)(ze)幅度(du)減(jian)小(xiao)0.1V；當(dang)(dang)(dang)(dang)(dang)7按(an)(an)(an)(an)(an)鍵(jian)(jian)按(an)(an)(an)(an)(an)下(xia)，則(ze)(ze)進行掃(sao)頻。當(dang)(dang)(dang)(dang)(dang)執(zhi)行完按(an)(an)(an)(an)(an)鍵(jian)(jian)程(cheng)序(xu)后(hou)，返回系(xi)統(tong)主程(cheng)序(xu)。
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(ji)好(hao)后，應滿足以下要求：
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(jiao)波 Up-p=6V，正弦波 Up-p>1V。
2、擴展性能指標要求
頻(pin)率范圍分(fen)段設置10Hz~100Hz，100Hz~1kHz，1kHz~10kHz；波(bo)形特性(xing)方波(bo)t r<30us（1kHz，最大輸(shu)出時），三(san)角波(bo)r△<2%，正弦波(bo)r～<5%。
