在PCB設(she)計中(zhong)，給信號提供(gong)一(yi)個(ge)穩定(ding)的(de)(de)電(dian)(dian)(dian)壓(ya)以(yi)及合適的(de)(de)電(dian)(dian)(dian)壓(ya)分配是電(dian)(dian)(dian)源(yuan)系(xi)統(tong)設(she)計中(zhong)的(de)(de)兩個(ge)基本目標。隨(sui)著信號完(wan)整性(xing)問題的(de)(de)出現，反射、串擾等(deng)都會影響到電(dian)(dian)(dian)源(yuan)系(xi)統(tong)的(de)(de)穩定(ding)，再加上芯片工作(zuo)(zuo)電(dian)(dian)(dian)壓(ya)的(de)(de)不(bu)斷減小(xiao)，電(dian)(dian)(dian)源(yuan)的(de)(de)波動(dong)性(xing)將會影響系(xi)統(tong)的(de)(de)正常工作(zuo)(zuo)。電(dian)(dian)(dian)源(yuan)完(wan)整性(xing)分析，就是為了(le)保(bao)證PCB中(zhong)有一(yi)個(ge)穩定(ding)可靠的(de)(de)電(dian)(dian)(dian)源(yuan)供(gong)應。

電源完整性分析概述

電(dian)(dian)(dian)源(yuan)(yuan)完整性就是指系統中電(dian)(dian)(dian)源(yuan)(yuan)波形的(de)質量。隨著IC輸出開關(guan)速度的(de)提高(gao)，信號的(de)邊沿(yan)速率(lv)即(ji)信號上升和下(xia)降的(de)時間(jian)迅速縮(suo)減，電(dian)(dian)(dian)源(yuan)(yuan)線由于(yu)它的(de)寄(ji)生(sheng)電(dian)(dian)(dian)感(gan)承受(shou)著不(bu)小的(de)電(dian)(dian)(dian)壓降。對于(yu)小于(yu)1ns的(de)信號邊沿(yan)速率(lv)，會(hui)造(zao)成PCB上電(dian)(dian)(dian)源(yuan)(yuan)層與地層間(jian)的(de)電(dian)(dian)(dian)壓在電(dian)(dian)(dian)路板(ban)的(de)各處不(bu)同，從而影(ying)響到芯片供(gong)電(dian)(dian)(dian)的(de)穩定性，甚至(zhi)會(hui)導致芯片的(de)邏輯

造(zao)成(cheng)電(dian)源系(xi)統不穩定(ding)的(de)(de)因(yin)素表現為(wei)同步(bu)開(kai)關噪(zao)(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)、非理(li)想電(dian)源阻抗影(ying)響(xiang)、諧振及邊緣(yuan)效應(ying)。一(yi)般情況下，同步(bu)開(kai)關噪(zao)(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)是電(dian)源噪(zao)(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)的(de)(de)主要來源。由于(yu)(yu)地(di)(di)引線和(he)平面(mian)存在寄生電(dian)感，在開(kai)關電(dian)流(liu)的(de)(de)作用(yong)下，會造(zao)成(cheng)一(yi)定(ding)的(de)(de)電(dian)壓波動，也(ye)就是說(shuo)，器件(jian)的(de)(de)參考地(di)(di)已不再(zai)是零電(dian)平，因(yin)此，驅動端(duan)要發送的(de)(de)地(di)(di)電(dian)平會出(chu)現相(xiang)應(ying)的(de)(de)干(gan)擾波形(xing)，干(gan)擾波形(xing)的(de)(de)相(xiang)位與(yu)地(di)(di)面(mian)噪(zao)(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)相(xiang)同，對于(yu)(yu)開(kai)關信號(hao)波形(xing)來說(shuo)，地(di)(di)噪(zao)(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)的(de)(de)影(ying)響(xiang)會導(dao)致信號(hao)的(de)(de)下降沿變緩；在接收端(duan)，信號(hao)的(de)(de)波形(xing)同樣(yang)會受(shou)到地(di)(di)噪(zao)(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)的(de)(de)干(gan)擾，但干(gan)擾波形(xing)的(de)(de)相(xiang)位與(yu)地(di)(di)面(mian)噪(zao)(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)相(xiang)反(fan)。另外(wai)，在一(yi)些存儲(chu)元器件(jian)中，有可(ke)能因(yin)為(wei)電(dian)源噪(zao)(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)和(he)地(di)(di)噪(zao)(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)造(zao)成(cheng)數據的(de)(de)意外(wai)翻轉。

在(zai)高頻(pin)電路(lu)(lu)中，電源(yuan)平(ping)面存在(zai)大量寄(ji)(ji)生參量，這些(xie)寄(ji)(ji)生參量可以(yi)看成(cheng)是由很多(duo)電感和電容(rong)構成(cheng)的(de)(de)(de)LC諧(xie)(xie)振網絡(luo)，或諧(xie)(xie)振腔。在(zai)某(mou)一確定的(de)(de)(de)頻(pin)率下(xia)，這些(xie)電容(rong)和電感將發生諧(xie)(xie)振現(xian)象(xiang)，從而影響(xiang)電源(yuan)層的(de)(de)(de)阻(zu)抗(kang)。除了諧(xie)(xie)振效(xiao)(xiao)應，電源(yuan)平(ping)面和地(di)平(ping)面的(de)(de)(de)邊(bian)緣(yuan)效(xiao)(xiao)應也是電源(yuan)設計中需(xu)要注意的(de)(de)(de)問題(ti)，這里(li)的(de)(de)(de)邊(bian)緣(yuan)效(xiao)(xiao)應指邊(bian)緣(yuan)反射(she)和輻射(she)現(xian)象(xiang)。電路(lu)(lu)板邊(bian)緣(yuan)覆銅面大小受到(dao)限制，故容(rong)易(yi)產生電磁干擾問題(ti)。工程中通常添(tian)加去耦電容(rong)，以(yi)減小邊(bian)緣(yuan)的(de)(de)(de)輻射(she)效(xiao)(xiao)應，達到(dao)抑制電源(yuan)平(ping)面噪聲(sheng)的(de)(de)(de)目(mu)的(de)(de)(de)。

同步開關噪聲

同步(bu)開(kai)(kai)(kai)關(guan)噪(zao)聲（SSN）主(zhu)要由(you)伴隨(sui)著器(qi)件的(de)同步(bu)開(kai)(kai)(kai)關(guan)輸(shu)出產生。開(kai)(kai)(kai)關(guan)速度越快，瞬間電流變化越顯著，電流回(hui)路上的(de)電感越大，則(ze)產生的(de)同步(bu)開(kai)(kai)(kai)關(guan)噪(zao)聲越嚴重。由(you)此可(ke)見，同步(bu)開(kai)(kai)(kai)關(guan)噪(zao)聲的(de)大小(xiao)取(qu)決(jue)于集成電路的(de)I/O特性、PCB板(ban)電源(yuan)平(ping)(ping)面和地平(ping)(ping)面的(de)阻抗，以(yi)及(ji)高(gao)速器(qi)件在PCB上的(de)布(bu)局(ju)和布(bu)線方式。

根據回流(liu)路徑的(de)不同，同步開(kai)(kai)關(guan)噪(zao)(zao)聲可(ke)分(fen)為芯(xin)片(pian)(pian)外開(kai)(kai)關(guan)噪(zao)(zao)聲和(he)(he)(he)芯(xin)片(pian)(pian)內(nei)開(kai)(kai)關(guan)噪(zao)(zao)聲。芯(xin)片(pian)(pian)外開(kai)(kai)關(guan)噪(zao)(zao)聲是指信(xin)號(hao)開(kai)(kai)關(guan)引發的(de)電(dian)流(liu)回流(liu)經(jing)過(guo)信(xin)號(hao)線(xian)、電(dian)源(yuan)/地(di)平面時產生的(de)噪(zao)(zao)聲；如(ru)果開(kai)(kai)關(guan)狀態轉變(bian)時，電(dian)流(liu)的(de)回流(liu)路徑經(jing)過(guo)電(dian)源(yuan)和(he)(he)(he)地(di)，而不是信(xin)號(hao)線(xian)，此時的(de)噪(zao)(zao)聲為芯(xin)片(pian)(pian)內(nei)開(kai)(kai)關(guan)噪(zao)(zao)聲。減(jian)(jian)小芯(xin)片(pian)(pian)內(nei)開(kai)(kai)關(guan)噪(zao)(zao)聲主要(yao)通過(guo)減(jian)(jian)小開(kai)(kai)關(guan)信(xin)號(hao)流(liu)經(jing)路徑的(de)電(dian)感或減(jian)(jian)緩(huan)開(kai)(kai)關(guan)信(xin)號(hao)的(de)變(bian)化速率減(jian)(jian)小感應電(dian)壓來實現。減(jian)(jian)小芯(xin)片(pian)(pian)外開(kai)(kai)關(guan)噪(zao)(zao)聲可(ke)以通過(guo)降低芯(xin)片(pian)(pian)內(nei)部驅動器的(de)開(kai)(kai)關(guan)速率和(he)(he)(he)同時開(kai)(kai)關(guan)的(de)數目，采用能滿足時序(xu)要(yao)求的(de)最(zui)慢(man)邊(bian)沿速率的(de)芯(xin)片(pian)(pian)；或通過(guo)降低封(feng)裝回路電(dian)感，增加信(xin)號(hao)和(he)(he)(he)電(dian)源(yuan)與地(di)的(de)耦合(he)電(dian)感；也可(ke)在封(feng)裝內(nei)部使(shi)用旁路電(dian)容(rong)，讓電(dian)源(yuan)和(he)(he)(he)地(di)共同分(fen)擔電(dian)流(liu)回路，減(jian)(jian)小回流(liu)路徑的(de)等效電(dian)感。

電源分配設計

電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)噪聲在(zai)很大(da)程度上源(yuan)(yuan)(yuan)(yuan)于(yu)非理想(xiang)的(de)(de)(de)電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)分(fen)配系統。電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)分(fen)配系統就是給(gei)系統內(nei)(nei)的(de)(de)(de)所有(you)器(qi)(qi)件(jian)提供足(zu)夠的(de)(de)(de)電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)，這些器(qi)(qi)件(jian)不(bu)但需要(yao)足(zu)夠的(de)(de)(de)功率(lv)損耗，同時(shi)對電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)的(de)(de)(de)平穩性也有(you)一(yi)定(ding)的(de)(de)(de)要(yao)求。因為(wei)(wei)實(shi)際電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)平面總存在(zai)著阻(zu)(zu)抗(kang)，在(zai)有(you)瞬(shun)間電(dian)(dian)(dian)(dian)流(liu)通過(guo)時(shi)，就會(hui)產生電(dian)(dian)(dian)(dian)壓降，從(cong)而導致電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)的(de)(de)(de)波動。大(da)部分(fen)器(qi)(qi)件(jian)對電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)波動的(de)(de)(de)要(yao)求在(zai)正(zheng)常電(dian)(dian)(dian)(dian)壓的(de)(de)(de)±5%范圍(wei)內(nei)(nei)。為(wei)(wei)了保證(zheng)每(mei)個器(qi)(qi)件(jian)都能正(zheng)常工作，應(ying)該盡可(ke)能的(de)(de)(de)降低(di)(di)電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)平面的(de)(de)(de)阻(zu)(zu)抗(kang)。在(zai)工作頻率(lv)比(bi)較高的(de)(de)(de)情況(kuang)下，既要(yao)計算電(dian)(dian)(dian)(dian)阻(zu)(zu)的(de)(de)(de)直流(liu)阻(zu)(zu)抗(kang)，還要(yao)計算由電(dian)(dian)(dian)(dian)感(gan)引起的(de)(de)(de)交(jiao)流(liu)阻(zu)(zu)抗(kang)。在(zai)對電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)阻(zu)(zu)抗(kang)進行控制(zhi)時(shi)，可(ke)通過(guo)采(cai)用電(dian)(dian)(dian)(dian)阻(zu)(zu)率(lv)低(di)(di)的(de)(de)(de)材料，采(cai)用短(duan)而粗厚的(de)(de)(de)電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)線，減小電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)內(nei)(nei)阻(zu)(zu)，電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)盡量靠近地，使用去耦(ou)電(dian)(dian)(dian)(dian)容等方法，以(yi)減小電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)的(de)(de)(de)電(dian)(dian)(dian)(dian)阻(zu)(zu)和電(dian)(dian)(dian)(dian)感(gan)，從(cong)而降低(di)(di)電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)阻(zu)(zu)抗(kang)。