在PCB設計中，給(gei)信號提(ti)供(gong)一(yi)個(ge)穩(wen)(wen)定(ding)(ding)(ding)的(de)(de)電(dian)(dian)壓(ya)以(yi)及合(he)適的(de)(de)電(dian)(dian)壓(ya)分配是電(dian)(dian)源(yuan)系(xi)(xi)(xi)統(tong)(tong)設計中的(de)(de)兩個(ge)基本目標。隨著信號完整性問題(ti)的(de)(de)出現(xian)，反射、串擾等都會(hui)影響(xiang)到電(dian)(dian)源(yuan)系(xi)(xi)(xi)統(tong)(tong)的(de)(de)穩(wen)(wen)定(ding)(ding)(ding)，再加上芯(xin)片工作電(dian)(dian)壓(ya)的(de)(de)不斷減(jian)小(xiao)，電(dian)(dian)源(yuan)的(de)(de)波動性將會(hui)影響(xiang)系(xi)(xi)(xi)統(tong)(tong)的(de)(de)正常工作。電(dian)(dian)源(yuan)完整性分析，就是為了(le)保(bao)證PCB中有(you)一(yi)個(ge)穩(wen)(wen)定(ding)(ding)(ding)可靠的(de)(de)電(dian)(dian)源(yuan)供(gong)應。

電源完整性分析概述

電(dian)(dian)源(yuan)完整性(xing)就是指系(xi)統(tong)中電(dian)(dian)源(yuan)波(bo)形的(de)(de)(de)質量。隨著(zhu)IC輸出開(kai)關速(su)度的(de)(de)(de)提高，信號(hao)的(de)(de)(de)邊沿速(su)率即信號(hao)上升和下降(jiang)的(de)(de)(de)時間迅(xun)速(su)縮減，電(dian)(dian)源(yuan)線由于它的(de)(de)(de)寄生電(dian)(dian)感承受著(zhu)不(bu)小(xiao)的(de)(de)(de)電(dian)(dian)壓降(jiang)。對(dui)于小(xiao)于1ns的(de)(de)(de)信號(hao)邊沿速(su)率，會造成PCB上電(dian)(dian)源(yuan)層與地層間的(de)(de)(de)電(dian)(dian)壓在電(dian)(dian)路板的(de)(de)(de)各處不(bu)同(tong)，從而影響到芯片供電(dian)(dian)的(de)(de)(de)穩定性(xing)，甚至會導致芯片的(de)(de)(de)邏輯

造(zao)成(cheng)電(dian)(dian)源(yuan)系(xi)統不穩定的(de)因(yin)(yin)素表現為同步(bu)開關(guan)噪(zao)(zao)(zao)(zao)聲(sheng)(sheng)、非理想電(dian)(dian)源(yuan)阻抗影響、諧振及邊緣效應。一(yi)般情況(kuang)下，同步(bu)開關(guan)噪(zao)(zao)(zao)(zao)聲(sheng)(sheng)是電(dian)(dian)源(yuan)噪(zao)(zao)(zao)(zao)聲(sheng)(sheng)的(de)主(zhu)要來(lai)(lai)源(yuan)。由于(yu)地(di)(di)(di)引線和(he)平(ping)面(mian)存在(zai)(zai)(zai)寄生(sheng)電(dian)(dian)感，在(zai)(zai)(zai)開關(guan)電(dian)(dian)流的(de)作用(yong)下，會(hui)造(zao)成(cheng)一(yi)定的(de)電(dian)(dian)壓(ya)波動，也就是說，器件的(de)參(can)考(kao)地(di)(di)(di)已(yi)不再是零電(dian)(dian)平(ping)，因(yin)(yin)此，驅動端要發(fa)送的(de)地(di)(di)(di)電(dian)(dian)平(ping)會(hui)出現相應的(de)干(gan)擾波形(xing)，干(gan)擾波形(xing)的(de)相位與(yu)地(di)(di)(di)面(mian)噪(zao)(zao)(zao)(zao)聲(sheng)(sheng)相同，對于(yu)開關(guan)信號(hao)波形(xing)來(lai)(lai)說，地(di)(di)(di)噪(zao)(zao)(zao)(zao)聲(sheng)(sheng)的(de)影響會(hui)導致信號(hao)的(de)下降沿變緩；在(zai)(zai)(zai)接收端，信號(hao)的(de)波形(xing)同樣會(hui)受到地(di)(di)(di)噪(zao)(zao)(zao)(zao)聲(sheng)(sheng)的(de)干(gan)擾，但干(gan)擾波形(xing)的(de)相位與(yu)地(di)(di)(di)面(mian)噪(zao)(zao)(zao)(zao)聲(sheng)(sheng)相反(fan)。另(ling)外，在(zai)(zai)(zai)一(yi)些存儲元器件中，有可能因(yin)(yin)為電(dian)(dian)源(yuan)噪(zao)(zao)(zao)(zao)聲(sheng)(sheng)和(he)地(di)(di)(di)噪(zao)(zao)(zao)(zao)聲(sheng)(sheng)造(zao)成(cheng)數據的(de)意外翻轉(zhuan)。

在高頻電(dian)路(lu)中，電(dian)源(yuan)平面存在大(da)量寄(ji)生(sheng)參量，這(zhe)些寄(ji)生(sheng)參量可(ke)以看成(cheng)是(shi)由很(hen)多電(dian)感和電(dian)容(rong)構成(cheng)的(de)(de)(de)LC諧(xie)(xie)振網絡，或諧(xie)(xie)振腔。在某一確定的(de)(de)(de)頻率下(xia)，這(zhe)些電(dian)容(rong)和電(dian)感將發(fa)生(sheng)諧(xie)(xie)振現象(xiang)，從而影(ying)響電(dian)源(yuan)層的(de)(de)(de)阻抗。除(chu)了諧(xie)(xie)振效(xiao)(xiao)應(ying)，電(dian)源(yuan)平面和地平面的(de)(de)(de)邊(bian)(bian)緣效(xiao)(xiao)應(ying)也是(shi)電(dian)源(yuan)設計中需要注意(yi)的(de)(de)(de)問題，這(zhe)里的(de)(de)(de)邊(bian)(bian)緣效(xiao)(xiao)應(ying)指(zhi)邊(bian)(bian)緣反射和輻射現象(xiang)。電(dian)路(lu)板邊(bian)(bian)緣覆銅面大(da)小受到限制，故容(rong)易產生(sheng)電(dian)磁干擾問題。工程(cheng)中通常(chang)添加(jia)去耦電(dian)容(rong)，以減小邊(bian)(bian)緣的(de)(de)(de)輻射效(xiao)(xiao)應(ying)，達到抑(yi)制電(dian)源(yuan)平面噪聲(sheng)的(de)(de)(de)目的(de)(de)(de)。

同步開關噪聲

同(tong)(tong)步(bu)(bu)開(kai)關(guan)噪(zao)聲（SSN）主要由伴隨著器(qi)件的(de)(de)同(tong)(tong)步(bu)(bu)開(kai)關(guan)輸出(chu)產生。開(kai)關(guan)速(su)度(du)越(yue)(yue)(yue)快，瞬間電流變(bian)化越(yue)(yue)(yue)顯著，電流回路上的(de)(de)電感越(yue)(yue)(yue)大，則產生的(de)(de)同(tong)(tong)步(bu)(bu)開(kai)關(guan)噪(zao)聲越(yue)(yue)(yue)嚴重。由此可見(jian)，同(tong)(tong)步(bu)(bu)開(kai)關(guan)噪(zao)聲的(de)(de)大小(xiao)取決于集成(cheng)電路的(de)(de)I/O特性、PCB板電源平面和(he)(he)地平面的(de)(de)阻抗，以及(ji)高速(su)器(qi)件在PCB上的(de)(de)布局和(he)(he)布線方式。

根據回流(liu)(liu)路徑的(de)(de)不同，同步開(kai)(kai)(kai)(kai)關(guan)(guan)(guan)噪(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)可(ke)(ke)分為芯(xin)(xin)(xin)(xin)片(pian)(pian)外(wai)開(kai)(kai)(kai)(kai)關(guan)(guan)(guan)噪(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)和芯(xin)(xin)(xin)(xin)片(pian)(pian)內開(kai)(kai)(kai)(kai)關(guan)(guan)(guan)噪(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)。芯(xin)(xin)(xin)(xin)片(pian)(pian)外(wai)開(kai)(kai)(kai)(kai)關(guan)(guan)(guan)噪(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)是指(zhi)信(xin)(xin)號(hao)(hao)開(kai)(kai)(kai)(kai)關(guan)(guan)(guan)引發的(de)(de)電(dian)(dian)(dian)流(liu)(liu)回流(liu)(liu)經(jing)(jing)過(guo)信(xin)(xin)號(hao)(hao)線、電(dian)(dian)(dian)源(yuan)/地(di)平(ping)面時(shi)產生的(de)(de)噪(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)；如果(guo)開(kai)(kai)(kai)(kai)關(guan)(guan)(guan)狀態轉變時(shi)，電(dian)(dian)(dian)流(liu)(liu)的(de)(de)回流(liu)(liu)路徑經(jing)(jing)過(guo)電(dian)(dian)(dian)源(yuan)和地(di)，而不是信(xin)(xin)號(hao)(hao)線，此時(shi)的(de)(de)噪(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)為芯(xin)(xin)(xin)(xin)片(pian)(pian)內開(kai)(kai)(kai)(kai)關(guan)(guan)(guan)噪(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)。減小(xiao)芯(xin)(xin)(xin)(xin)片(pian)(pian)內開(kai)(kai)(kai)(kai)關(guan)(guan)(guan)噪(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)主要通過(guo)減小(xiao)開(kai)(kai)(kai)(kai)關(guan)(guan)(guan)信(xin)(xin)號(hao)(hao)流(liu)(liu)經(jing)(jing)路徑的(de)(de)電(dian)(dian)(dian)感(gan)(gan)或(huo)減緩開(kai)(kai)(kai)(kai)關(guan)(guan)(guan)信(xin)(xin)號(hao)(hao)的(de)(de)變化速率減小(xiao)感(gan)(gan)應電(dian)(dian)(dian)壓來(lai)實現。減小(xiao)芯(xin)(xin)(xin)(xin)片(pian)(pian)外(wai)開(kai)(kai)(kai)(kai)關(guan)(guan)(guan)噪(zao)(zao)聲(sheng)(sheng)(sheng)(sheng)可(ke)(ke)以通過(guo)降低芯(xin)(xin)(xin)(xin)片(pian)(pian)內部(bu)(bu)驅動器(qi)的(de)(de)開(kai)(kai)(kai)(kai)關(guan)(guan)(guan)速率和同時(shi)開(kai)(kai)(kai)(kai)關(guan)(guan)(guan)的(de)(de)數目(mu)，采用(yong)能(neng)滿(man)足時(shi)序要求的(de)(de)最慢邊沿速率的(de)(de)芯(xin)(xin)(xin)(xin)片(pian)(pian)；或(huo)通過(guo)降低封(feng)裝(zhuang)回路電(dian)(dian)(dian)感(gan)(gan)，增加信(xin)(xin)號(hao)(hao)和電(dian)(dian)(dian)源(yuan)與地(di)的(de)(de)耦(ou)合電(dian)(dian)(dian)感(gan)(gan)；也可(ke)(ke)在(zai)封(feng)裝(zhuang)內部(bu)(bu)使用(yong)旁路電(dian)(dian)(dian)容，讓電(dian)(dian)(dian)源(yuan)和地(di)共同分擔電(dian)(dian)(dian)流(liu)(liu)回路，減小(xiao)回流(liu)(liu)路徑的(de)(de)等效電(dian)(dian)(dian)感(gan)(gan)。

電源分配設計

電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)噪聲在(zai)(zai)很大程度上源(yuan)(yuan)(yuan)(yuan)于非理想的(de)(de)(de)電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)分(fen)配(pei)系統(tong)(tong)。電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)分(fen)配(pei)系統(tong)(tong)就是給系統(tong)(tong)內(nei)的(de)(de)(de)所有(you)器(qi)件提(ti)供(gong)足(zu)夠的(de)(de)(de)電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)，這些器(qi)件不但需要足(zu)夠的(de)(de)(de)功(gong)率損耗，同時對(dui)(dui)電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)的(de)(de)(de)平(ping)穩(wen)性(xing)也有(you)一定的(de)(de)(de)要求。因為實際(ji)電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)平(ping)面(mian)總存在(zai)(zai)著阻(zu)(zu)(zu)抗(kang)(kang)，在(zai)(zai)有(you)瞬間(jian)電(dian)(dian)(dian)流通過時，就會產生電(dian)(dian)(dian)壓降(jiang)(jiang)，從而導致電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)的(de)(de)(de)波動(dong)。大部(bu)分(fen)器(qi)件對(dui)(dui)電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)波動(dong)的(de)(de)(de)要求在(zai)(zai)正(zheng)(zheng)常(chang)(chang)電(dian)(dian)(dian)壓的(de)(de)(de)±5%范圍內(nei)。為了保證每個器(qi)件都能正(zheng)(zheng)常(chang)(chang)工作，應(ying)該盡可(ke)能的(de)(de)(de)降(jiang)(jiang)低(di)電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)平(ping)面(mian)的(de)(de)(de)阻(zu)(zu)(zu)抗(kang)(kang)。在(zai)(zai)工作頻率比較(jiao)高的(de)(de)(de)情況下(xia)，既要計算電(dian)(dian)(dian)阻(zu)(zu)(zu)的(de)(de)(de)直流阻(zu)(zu)(zu)抗(kang)(kang)，還要計算由電(dian)(dian)(dian)感引起的(de)(de)(de)交流阻(zu)(zu)(zu)抗(kang)(kang)。在(zai)(zai)對(dui)(dui)電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)阻(zu)(zu)(zu)抗(kang)(kang)進行控制時，可(ke)通過采(cai)用(yong)(yong)電(dian)(dian)(dian)阻(zu)(zu)(zu)率低(di)的(de)(de)(de)材料，采(cai)用(yong)(yong)短而粗厚的(de)(de)(de)電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)線(xian)，減小電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)內(nei)阻(zu)(zu)(zu)，電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)盡量靠近地，使用(yong)(yong)去耦電(dian)(dian)(dian)容(rong)等方法，以減小電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)的(de)(de)(de)電(dian)(dian)(dian)阻(zu)(zu)(zu)和電(dian)(dian)(dian)感，從而降(jiang)(jiang)低(di)電(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)阻(zu)(zu)(zu)抗(kang)(kang)。