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穿心電容濾波的兩個重要注意事項
我們采取穿心電容濾波時要達到濾波效果，必須選取合適的穿心電容以及接干擾比較小的!穿心電容可以根據器件手冊與經驗，有經驗工程師在前期原理圖以及PCB時要考慮.
穿(chuan)心電容(rong)(rong)(rong)在EMC設計中非常重要(yao)，也是我們常用的濾(lv)(lv)波元件!但在我培訓的過程中發現，大家對穿(chuan)心電容(rong)(rong)(rong)的使用并(bing)不(bu)是很(hen)明確!這里(li)我們把穿(chuan)心穿(chuan)心電容(rong)(rong)(rong)濾(lv)(lv)波的2個要(yao)點介紹一下(xia)：
1、穿心(xin)(xin)電(dian)容(rong)選(xuan)好(hao)了，不(bu)代(dai)表就能(neng)(neng)濾(lv)除干擾(rao)!河水(shui)(shui)泛濫，到達高水(shui)(shui)位(wei)，這時我們(men)往往會增加一(yi)條溝渠(qu)(qu)引(yin)流，那么引(yin)到的(de)(de)(de)地(di)方必須(xu)是一(yi)個(ge)低水(shui)(shui)位(wei)的(de)(de)(de)，如果引(yin)到一(yi)個(ge)高水(shui)(shui)位(wei)的(de)(de)(de)水(shui)(shui)庫的(de)(de)(de)話，反而會引(yin)起水(shui)(shui)倒(dao)灌，抬(tai)高水(shui)(shui)位(wei)。穿心(xin)(xin)電(dian)容(rong)濾(lv)波與治水(shui)(shui)問(wen)題是一(yi)樣得，穿心(xin)(xin)電(dian)容(rong)只(zhi)是起到一(yi)個(ge)溝渠(qu)(qu)得作(zuo)用(yong)，能(neng)(neng)否濾(lv)波還取決與穿心(xin)(xin)電(dian)容(rong)接的(de)(de)(de)地(di)上(shang)(shang)干擾(rao)的(de)(de)(de)大小(xiao)(xiao)(xiao)。我們(men)經常發現(xian)工程(cheng)師解(jie)決干擾(rao)問(wen)題加穿心(xin)(xin)電(dian)容(rong)沒有(you)效果，有(you)很大程(cheng)度是地(di)上(shang)(shang)干擾(rao)本(ben)身(shen)很大!反而把地(di)上(shang)(shang)干擾(rao)引(yin)到信號(hao)或電(dian)源上(shang)(shang)來!大家需(xu)要(yao)注(zhu)意，地(di)上(shang)(shang)干擾(rao)在有(you)些(xie)情(qing)況(kuang)小(xiao)(xiao)(xiao)并不(bu)是較(jiao)小(xiao)(xiao)(xiao)的(de)(de)(de)!所以我們(men)強調濾(lv)波有(you)一(yi)個(ge)重要(yao)的(de)(de)(de)基礎(chu)，就是所接的(de)(de)(de)地(di)要(yao)干擾(rao)小(xiao)(xiao)(xiao)，就是通常說(shuo)的(de)(de)(de)“靜(jing)地(di)”。
2、穿(chuan)心(xin)(xin)(xin)電(dian)(dian)容(rong)(rong)(rong)濾(lv)波是(shi)(shi)有(you)(you)頻(pin)段(duan)的(de)，很(hen)多人以(yi)(yi)為穿(chuan)心(xin)(xin)(xin)電(dian)(dian)容(rong)(rong)(rong)是(shi)(shi)越大(da)越好，其實(shi)不(bu)然，每個穿(chuan)心(xin)(xin)(xin)電(dian)(dian)容(rong)(rong)(rong)有(you)(you)一定的(de)濾(lv)波頻(pin)段(duan)，大(da)穿(chuan)心(xin)(xin)(xin)電(dian)(dian)容(rong)(rong)(rong)濾(lv)低頻(pin)，小(xiao)穿(chuan)心(xin)(xin)(xin)電(dian)(dian)容(rong)(rong)(rong)濾(lv)高頻(pin)，主要是(shi)(shi)根據穿(chuan)心(xin)(xin)(xin)電(dian)(dian)容(rong)(rong)(rong)的(de)諧(xie)振(zhen)(zhen)(zhen)頻(pin)點來決(jue)定，穿(chuan)心(xin)(xin)(xin)電(dian)(dian)容(rong)(rong)(rong)在(zai)(zai)(zai)(zai)諧(xie)振(zhen)(zhen)(zhen)頻(pin)率(lv)點處(chu)有(you)(you)具佳的(de)濾(lv)波效果!在(zai)(zai)(zai)(zai)以(yi)(yi)諧(xie)振(zhen)(zhen)(zhen)點為中心(xin)(xin)(xin)的(de)一段(duan)頻(pin)段(duan)之(zhi)內有(you)(you)較好的(de)濾(lv)波效果，其他部分濾(lv)波效果不(bu)佳!穿(chuan)心(xin)(xin)(xin)電(dian)(dian)容(rong)(rong)(rong)的(de)諧(xie)振(zhen)(zhen)(zhen)點與(yu)穿(chuan)心(xin)(xin)(xin)電(dian)(dian)容(rong)(rong)(rong)的(de)容(rong)(rong)(rong)值以(yi)(yi)及ESL(等效串聯電(dian)(dian)感)相關，具體大(da)家可以(yi)(yi)查一下網上(shang)資料，以(yi)(yi)及會議(yi)學校(xiao)學習串聯諧(xie)振(zhen)(zhen)(zhen)電(dian)(dian)路(lu)的(de)理論分析就會知道!通常我(wo)們建(jian)議(yi)在(zai)(zai)(zai)(zai)電(dian)(dian)源端(duan)口增(zeng)加UF級(ji)別穿(chuan)心(xin)(xin)(xin)電(dian)(dian)容(rong)(rong)(rong)來濾(lv)波幾百KHZ到(dao)5MHZ之(zhi)間的(de)差模干(gan)(gan)擾，原因就是(shi)(shi)UF級(ji)別穿(chuan)心(xin)(xin)(xin)電(dian)(dian)容(rong)(rong)(rong)諧(xie)振(zhen)(zhen)(zhen)點在(zai)(zai)(zai)(zai)1MHZ左右。另外(wai)建(jian)議(yi)加在(zai)(zai)(zai)(zai)高頻(pin)數字電(dian)(dian)路(lu)上(shang)我(wo)們建(jian)議(yi)加1nF貼(tie)片(pian)穿(chuan)心(xin)(xin)(xin)電(dian)(dian)容(rong)(rong)(rong)，原因就是(shi)(shi)1nf穿(chuan)心(xin)(xin)(xin)電(dian)(dian)容(rong)(rong)(rong)的(de)諧(xie)振(zhen)(zhen)(zhen)頻(pin)率(lv)在(zai)(zai)(zai)(zai)100MHZ之(zhi)間，不(bu)同廠家諧(xie)振(zhen)(zhen)(zhen)頻(pin)點有(you)(you)所(suo)不(bu)同，這樣(yang)比較好濾(lv)波幾十MHZ到(dao)200MHZ干(gan)(gan)擾，有(you)(you)利與(yu)EMI問題解決(jue)!
所以(yi)說，我(wo)們采(cai)取穿(chuan)心(xin)電(dian)容濾(lv)波時(shi)要(yao)(yao)達到(dao)濾(lv)波效果，必須選取合適的(de)穿(chuan)心(xin)電(dian)容以(yi)及接干擾比(bi)較小的(de)!穿(chuan)心(xin)電(dian)容可以(yi)根據器件手冊與(yu)經驗，干擾小的(de)地可以(yi)在調(diao)試(shi)時(shi)采(cai)取儀器方(fang)法，有經驗工程師(shi)在前期原理圖以(yi)及PCB時(shi)要(yao)(yao)考慮。
