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　傳感器電路(lu)通常用來測量(liang)微弱的(de)(de)信(xin)號(hao)(hao)，具有(you)(you)很高(gao)的(de)(de)靈敏度(du)，但也很容易(yi)接(jie)收到外(wai)界或內部一些無規(gui)則(ze)(ze)的(de)(de)噪(zao)聲或干(gan)(gan)擾信(xin)號(hao)(hao)，如果這些噪(zao)聲和(he)(he)干(gan)(gan)擾的(de)(de)大小可以(yi)(yi)(yi)與有(you)(you)用信(xin)號(hao)(hao)相比(bi)較，那么在傳感器(qi)電路(lu)的(de)(de)輸出端有(you)(you)用信(xin)號(hao)(hao)將有(you)(you)可能被(bei)淹沒，或由于有(you)(you)用信(xin)號(hao)(hao)分(fen)(fen)量(liang)和(he)(he)噪(zao)聲干(gan)(gan)擾分(fen)(fen)量(liang)難以(yi)(yi)(yi)分(fen)(fen)辨，則(ze)(ze)必將妨礙對有(you)(you)用信(xin)號(hao)(hao)的(de)(de)測量(liang)。所以(yi)(yi)(yi)在傳感器(qi)電路(lu)的(de)(de)設計中，往(wang)往(wang)抗干(gan)(gan)擾設計是傳感器(qi)電路(lu)設計是否成功的(de)(de)關鍵。

　　高頻熱噪聲是由于導電體內部電子的無規則運動產生的。溫度越高，電子運動就越激烈。導體內部電子的無規則運動會在其內部形成很多微小的電流波動，因其是無序運動，故它的平均總電流為零，但當它作為一個元件(或作為電路的一部分)被接入放大電路后，其內部的電流就會被放大成為噪聲源，特別是對(dui)工作在高頻頻段(duan)內(nei)的電路(lu)高頻熱噪聲影(ying)響尤甚(shen)。

　　低頻噪聲(sheng)主要是由(you)于內部(bu)的(de)導(dao)(dao)電(dian)(dian)微粒(li)不(bu)連(lian)續造成的(de)。特別是碳膜(mo)電(dian)(dian)阻(zu)，其碳質材(cai)料內部(bu)存在許(xu)多微小顆粒(li)，顆粒(li)之間(jian)是不(bu)連(lian)續的(de)，在電(dian)(dian)流(liu)流(liu)過時，會使電(dian)(dian)阻(zu)的(de)導(dao)(dao)電(dian)(dian)率發生(sheng)(sheng)變化引(yin)起電(dian)(dian)流(liu)的(de)變化，產(chan)生(sheng)(sheng)類似(si)(si)接觸不(bu)良的(de)閃爆電(dian)(dian)弧。另外，晶體管也(ye)可能產(chan)生(sheng)(sheng)相(xiang)似(si)(si)的(de)爆裂(lie)噪聲(sheng)和閃爍噪聲(sheng)，其產(chan)生(sheng)(sheng)機理與(yu)電(dian)(dian)阻(zu)中微粒(li)的(de)不(bu)連(lian)續性相(xiang)近，也(ye)與(yu)晶體管的(de)摻雜程度(du)有關。

　　由于半(ban)導體(ti)PN結(jie)兩端(duan)勢(shi)壘區(qu)(qu)(qu)(qu)(qu)電(dian)(dian)(dian)壓的(de)變(bian)化引(yin)起(qi)累積(ji)在此區(qu)(qu)(qu)(qu)(qu)域的(de)電(dian)(dian)(dian)荷數量改(gai)變(bian)，從(cong)而顯(xian)現出電(dian)(dian)(dian)容效應。當(dang)外(wai)加正(zheng)向電(dian)(dian)(dian)壓升(sheng)高時(shi)，N區(qu)(qu)(qu)(qu)(qu)的(de)電(dian)(dian)(dian)子(zi)(zi)和(he)(he)P區(qu)(qu)(qu)(qu)(qu)的(de)空穴向耗(hao)盡區(qu)(qu)(qu)(qu)(qu)運動，相(xiang)當(dang)于對電(dian)(dian)(dian)容充電(dian)(dian)(dian)。當(dang)正(zheng)向電(dian)(dian)(dian)壓減小(xiao)時(shi)，它又使電(dian)(dian)(dian)子(zi)(zi)和(he)(he)空穴遠(yuan)離(li)耗(hao)盡區(qu)(qu)(qu)(qu)(qu)，相(xiang)當(dang)于電(dian)(dian)(dian)容放電(dian)(dian)(dian)。當(dang)外(wai)加反向電(dian)(dian)(dian)壓時(shi)，耗(hao)盡區(qu)(qu)(qu)(qu)(qu)的(de)變(bian)化相(xiang)反。當(dang)電(dian)(dian)(dian)流(liu)(liu)(liu)流(liu)(liu)(liu)經勢(shi)壘區(qu)(qu)(qu)(qu)(qu)時(shi)，這種變(bian)化會(hui)引(yin)起(qi)流(liu)(liu)(liu)過勢(shi)壘區(qu)(qu)(qu)(qu)(qu)的(de)電(dian)(dian)(dian)流(liu)(liu)(liu)產生(sheng)微小(xiao)波動，從(cong)而產生(sheng)電(dian)(dian)(dian)流(liu)(liu)(liu)噪(zao)聲(sheng)。其(qi)產生(sheng)噪(zao)聲(sheng)的(de)大小(xiao)與溫度(du)、頻帶寬度(du)△f成正(zheng)比。電(dian)(dian)(dian)路板上(shang)的(de)電(dian)(dian)(dian)磁元件的(de)干擾。

　　電(dian)(dian)(dian)(dian)(dian)阻(zu)的(de)(de)干擾(rao)來自于(yu)電(dian)(dian)(dian)(dian)(dian)阻(zu)中(zhong)的(de)(de)電(dian)(dian)(dian)(dian)(dian)感(gan)(gan)、電(dian)(dian)(dian)(dian)(dian)容效應和(he)電(dian)(dian)(dian)(dian)(dian)阻(zu)本身的(de)(de)熱噪聲(sheng)。例如一個阻(zu)值為R的(de)(de)實(shi)芯電(dian)(dian)(dian)(dian)(dian)阻(zu)，可(ke)(ke)等效為電(dian)(dian)(dian)(dian)(dian)阻(zu)R、寄(ji)生(sheng)電(dian)(dian)(dian)(dian)(dian)容C、寄(ji)生(sheng)電(dian)(dian)(dian)(dian)(dian)感(gan)(gan)L的(de)(de)串并聯(lian)。一般(ban)來說，寄(ji)生(sheng)電(dian)(dian)(dian)(dian)(dian)容為0.1～0.5pF，寄(ji)生(sheng)電(dian)(dian)(dian)(dian)(dian)感(gan)(gan)為5～8nH。在頻率高于(yu)1MHz時，這些寄(ji)生(sheng)電(dian)(dian)(dian)(dian)(dian)感(gan)(gan)電(dian)(dian)(dian)(dian)(dian)容就不可(ke)(ke)忽視了。