晶體振蕩器的選用

晶(jing)(jing)(jing)體(ti)(ti)(ti)(ti)(ti)振(zhen)(zhen)蕩(dang)(dang)器(qi)(qi)(qi)(qi)被廣(guang)泛應用(yong)到軍、民用(yong)通信(xin)電臺，微(wei)波通信(xin)設備，程控(kong)電話交換機(ji)，無線(xian)電綜合測試儀，BP機(ji)、移動(dong)電話發射臺，頻(pin)(pin)率計數(shu)器(qi)(qi)(qi)(qi)、GPS、遙控(kong)移動(dong)設備等。它(ta)有多(duo)種(zhong)(zhong)封裝，特(te)點是(shi)(shi)電氣(qi)性能(neng)規范多(duo)種(zhong)(zhong)多(duo)樣(yang)。它(ta)有好(hao)幾種(zhong)(zhong)不(bu)(bu)同(tong)的(de)(de)(de)(de)(de)類型：電壓控(kong)制(zhi)(zhi)晶(jing)(jing)(jing)體(ti)(ti)(ti)(ti)(ti)振(zhen)(zhen)蕩(dang)(dang)器(qi)(qi)(qi)(qi)（VCXO）、溫(wen)(wen)(wen)度(du)(du)(du)補(bu)償(chang)(chang)晶(jing)(jing)(jing)體(ti)(ti)(ti)(ti)(ti)振(zhen)(zhen)蕩(dang)(dang)器(qi)(qi)(qi)(qi)（TCXO）、恒溫(wen)(wen)(wen)晶(jing)(jing)(jing)體(ti)(ti)(ti)(ti)(ti)振(zhen)(zhen)蕩(dang)(dang)器(qi)(qi)(qi)(qi)（OCXO），以(yi)及數(shu)字(zi)補(bu)償(chang)(chang)晶(jing)(jing)(jing)體(ti)(ti)(ti)(ti)(ti)振(zhen)(zhen)蕩(dang)(dang)器(qi)(qi)(qi)(qi)（MCXO或(huo)(huo)(huo)DTCXO），每種(zhong)(zhong)類型都有自(zi)己的(de)(de)(de)(de)(de)性能(neng)。如(ru)果(guo)需(xu)要(yao)(yao)(yao)(yao)使設備即(ji)開即(ji)用(yong)，您就必(bi)須選用(yong)VCXO或(huo)(huo)(huo)溫(wen)(wen)(wen)補(bu)晶(jing)(jing)(jing)振(zhen)(zhen)，安(an)(an)防(fang)監控(kong)溫(wen)(wen)(wen)度(du)(du)(du)補(bu)償(chang)(chang)晶(jing)(jing)(jing)體(ti)(ti)(ti)(ti)(ti)振(zhen)(zhen)蕩(dang)(dang)器(qi)(qi)(qi)(qi)原廠，如(ru)果(guo)要(yao)(yao)(yao)(yao)求(qiu)穩(wen)(wen)(wen)(wen)(wen)定(ding)(ding)度(du)(du)(du)在(zai)0.5ppm以(yi)上，則需(xu)選擇數(shu)字(zi)溫(wen)(wen)(wen)補(bu)晶(jing)(jing)(jing)振(zhen)(zhen)（MCXO）。模擬溫(wen)(wen)(wen)補(bu)晶(jing)(jing)(jing)振(zhen)(zhen)適用(yong)于(yu)(yu)穩(wen)(wen)(wen)(wen)(wen)定(ding)(ding)度(du)(du)(du)要(yao)(yao)(yao)(yao)求(qiu)在(zai)5ppm～0.5ppm之間的(de)(de)(de)(de)(de)需(xu)求(qiu)。VCXO只適合于(yu)(yu)穩(wen)(wen)(wen)(wen)(wen)定(ding)(ding)度(du)(du)(du)要(yao)(yao)(yao)(yao)求(qiu)在(zai)5ppm以(yi)下(xia)的(de)(de)(de)(de)(de)產(chan)品。在(zai)不(bu)(bu)需(xu)要(yao)(yao)(yao)(yao)即(ji)開即(ji)用(yong)的(de)(de)(de)(de)(de)環境(jing)下(xia)，如(ru)果(guo)需(xu)要(yao)(yao)(yao)(yao)信(xin)號穩(wen)(wen)(wen)(wen)(wen)定(ding)(ding)度(du)(du)(du)超過0.1ppm的(de)(de)(de)(de)(de)，可(ke)(ke)選用(yong)OCXO。 晶(jing)(jing)(jing)體(ti)(ti)(ti)(ti)(ti)振(zhen)(zhen)蕩(dang)(dang)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)主要(yao)(yao)(yao)(yao)特(te)性之一(yi)是(shi)(shi)工作(zuo)溫(wen)(wen)(wen)度(du)(du)(du)內的(de)(de)(de)(de)(de)穩(wen)(wen)(wen)(wen)(wen)定(ding)(ding)性，它(ta)是(shi)(shi)決(jue)定(ding)(ding)振(zhen)(zhen)蕩(dang)(dang)器(qi)(qi)(qi)(qi)價格(ge)的(de)(de)(de)(de)(de)重要(yao)(yao)(yao)(yao)因(yin)素。穩(wen)(wen)(wen)(wen)(wen)定(ding)(ding)性愈(yu)高或(huo)(huo)(huo)溫(wen)(wen)(wen)度(du)(du)(du)范圍愈(yu)寬(kuan)，安(an)(an)防(fang)監控(kong)溫(wen)(wen)(wen)度(du)(du)(du)補(bu)償(chang)(chang)晶(jing)(jing)(jing)體(ti)(ti)(ti)(ti)(ti)振(zhen)(zhen)蕩(dang)(dang)器(qi)(qi)(qi)(qi)，器(qi)(qi)(qi)(qi)件的(de)(de)(de)(de)(de)價格(ge)亦(yi)愈(yu)高。工業級標(biao)準規定(ding)(ding)的(de)(de)(de)(de)(de)-40～+75℃這(zhe)(zhe)個范圍往往只是(shi)(shi)出(chu)于(yu)(yu)設計者們的(de)(de)(de)(de)(de)習慣，倘若-30～+70℃已經夠(gou)用(yong)，那么就不(bu)(bu)必(bi)去(qu)追求(qiu)更寬(kuan)的(de)(de)(de)(de)(de)溫(wen)(wen)(wen)度(du)(du)(du)范圍。設計工程師要(yao)(yao)(yao)(yao)慎(shen)密決(jue)定(ding)(ding)特(te)定(ding)(ding)應用(yong)的(de)(de)(de)(de)(de)實際需(xu)要(yao)(yao)(yao)(yao)，然后(hou)規定(ding)(ding)振(zhen)(zhen)蕩(dang)(dang)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)穩(wen)(wen)(wen)(wen)(wen)定(ding)(ding)度(du)(du)(du)。指(zhi)標(biao)過高意(yi)味著(zhu)花(hua)錢(qian)愈(yu)多(duo)。晶(jing)(jing)(jing)體(ti)(ti)(ti)(ti)(ti)老(lao)化(hua)(hua)是(shi)(shi)造(zao)成頻(pin)(pin)率變(bian)化(hua)(hua)的(de)(de)(de)(de)(de)又一(yi)重要(yao)(yao)(yao)(yao)因(yin)素。根據目(mu)標(biao)產(chan)品的(de)(de)(de)(de)(de)預期壽命不(bu)(bu)同(tong)，有多(duo)種(zhong)(zhong)方法可(ke)(ke)以(yi)減弱(ruo)這(zhe)(zhe)種(zhong)(zhong)影響。晶(jing)(jing)(jing)體(ti)(ti)(ti)(ti)(ti)老(lao)化(hua)(hua)會使輸(shu)出(chu)頻(pin)(pin)率按照對數(shu)曲線(xian)發生(sheng)變(bian)化(hua)(hua)，也就是(shi)(shi)說(shuo)在(zai)產(chan)品使用(yong)的(de)(de)(de)(de)(de)一(yi)年(nian)，這(zhe)(zhe)種(zhong)(zhong)現象才較(jiao)為顯著(zhu)。例如(ru)，安(an)(an)防(fang)監控(kong)溫(wen)(wen)(wen)度(du)(du)(du)補(bu)償(chang)(chang)晶(jing)(jing)(jing)體(ti)(ti)(ti)(ti)(ti)振(zhen)(zhen)蕩(dang)(dang)器(qi)(qi)(qi)(qi)單價，使用(yong)10年(nian)以(yi)上的(de)(de)(de)(de)(de)晶(jing)(jing)(jing)體(ti)(ti)(ti)(ti)(ti)，其老(lao)化(hua)(hua)速度(du)(du)(du)大約是(shi)(shi)一(yi)年(nian)的(de)(de)(de)(de)(de)3倍。采用(yong)特(te)殊的(de)(de)(de)(de)(de)晶(jing)(jing)(jing)體(ti)(ti)(ti)(ti)(ti)加工工藝(yi)可(ke)(ke)以(yi)改善這(zhe)(zhe)種(zhong)(zhong)情況，也可(ke)(ke)以(yi)采用(yong)調節的(de)(de)(de)(de)(de)辦法解決(jue)，安(an)(an)防(fang)監控(kong)溫(wen)(wen)(wen)度(du)(du)(du)補(bu)償(chang)(chang)晶(jing)(jing)(jing)體(ti)(ti)(ti)(ti)(ti)振(zhen)(zhen)蕩(dang)(dang)器(qi)(qi)(qi)(qi)廠家(jia)，比如(ru)，可(ke)(ke)以(yi)在(zai)控(kong)制(zhi)(zhi)引(yin)腳上施加電壓（即(ji)增加電壓控(kong)制(zhi)(zhi)功能(neng)）等。

晶振的分類

這類(lei)型晶(jing)振對溫度穩定性的(de)解決方案(an)采用(yong)了恒(heng)溫槽技術，將晶(jing)體置于(yu)恒(heng)溫槽內，通過設置恒(heng)溫工(gong)作點(dian)，使槽體保持恒(heng)溫狀態，在一定范(fan)圍(wei)內不受外(wai)界溫度影響(xiang)，達到穩定輸(shu)出頻率的(de)效果。這類(lei)晶(jing)振主要(yao)用(yong)于(yu)各種(zhong)類(lei)型的(de)通信(xin)設備，包(bao)括交換機、SDH傳輸(shu)設備、移動通信(xin)直放機、GPS接收機、電臺、數字(zi)電視等領(ling)域。根據用(yong)戶需要(yao)，該類(lei)型晶(jing)振可以帶(dai)壓控引(yin)腳。

晶體振(zhen)蕩器(qi)的基本原(yuan)理及特性(xing)

晶振(zhen)一般(ban)采用電(dian)(dian)(dian)容(rong)(rong)(rong)三端式(考(kao)畢茲) 交流等效(xiao)振(zhen)蕩(dang)電(dian)(dian)(dian)路(lu)；實際的(de)晶振(zhen)交流等效(xiao)電(dian)(dian)(dian)路(lu)其中 Cv 是(shi)(shi)用來調節振(zhen)蕩(dang)頻(pin)率(lv)，一般(ban)用變(bian)(bian)容(rong)(rong)(rong)二(er)極管(guan)加上不同的(de)反(fan)偏電(dian)(dian)(dian)壓來實現(xian)，這也(ye)是(shi)(shi)壓控(kong)作(zuo)用的(de)機(ji)理；把(ba)晶體(ti)(ti)的(de)等效(xiao)電(dian)(dian)(dian)路(lu)代(dai)替(ti)晶體(ti)(ti)后。其中 Co，C1，L1，RR 是(shi)(shi)晶體(ti)(ti)的(de)等效(xiao)電(dian)(dian)(dian)路(lu)。采用泛音次數(shu)越(yue)高的(de)晶振(zhen)，其等效(xiao)電(dian)(dian)(dian)容(rong)(rong)(rong) C1 就越(yue)小；因此頻(pin)率(lv)的(de)變(bian)(bian)化范圍(wei)也(ye)就越(yue)小。