在PCB設計中，給信號(hao)提供一個穩(wen)定的(de)電(dian)(dian)壓(ya)(ya)以及合適的(de)電(dian)(dian)壓(ya)(ya)分配是(shi)電(dian)(dian)源(yuan)系統設計中的(de)兩個基本目標。隨(sui)著信號(hao)完(wan)整性(xing)(xing)問題的(de)出(chu)現(xian)，反(fan)射、串擾(rao)等都會影響到(dao)電(dian)(dian)源(yuan)系統的(de)穩(wen)定，再加上芯片工(gong)作電(dian)(dian)壓(ya)(ya)的(de)不斷減小，電(dian)(dian)源(yuan)的(de)波(bo)動性(xing)(xing)將會影響系統的(de)正常工(gong)作。電(dian)(dian)源(yuan)完(wan)整性(xing)(xing)分析，就(jiu)是(shi)為了保證PCB中有一個穩(wen)定可靠(kao)的(de)電(dian)(dian)源(yuan)供應(ying)。

電源完整性分析概述

電(dian)(dian)源(yuan)完(wan)整性就是指系(xi)統中電(dian)(dian)源(yuan)波形的(de)(de)(de)(de)(de)質(zhi)量。隨著IC輸出開關速(su)(su)度的(de)(de)(de)(de)(de)提(ti)高，信(xin)號(hao)的(de)(de)(de)(de)(de)邊(bian)沿(yan)速(su)(su)率即(ji)信(xin)號(hao)上(shang)升(sheng)和下降的(de)(de)(de)(de)(de)時(shi)間(jian)迅速(su)(su)縮(suo)減，電(dian)(dian)源(yuan)線由于(yu)它的(de)(de)(de)(de)(de)寄生電(dian)(dian)感承(cheng)受著不小的(de)(de)(de)(de)(de)電(dian)(dian)壓降。對于(yu)小于(yu)1ns的(de)(de)(de)(de)(de)信(xin)號(hao)邊(bian)沿(yan)速(su)(su)率，會造成PCB上(shang)電(dian)(dian)源(yuan)層與地層間(jian)的(de)(de)(de)(de)(de)電(dian)(dian)壓在電(dian)(dian)路板的(de)(de)(de)(de)(de)各處不同(tong)，從而影(ying)響(xiang)到芯片(pian)供電(dian)(dian)的(de)(de)(de)(de)(de)穩定性，甚(shen)至會導致芯片(pian)的(de)(de)(de)(de)(de)邏(luo)輯

造(zao)成(cheng)電源(yuan)(yuan)系統不(bu)穩定的(de)(de)(de)(de)因(yin)素表現為(wei)同(tong)步(bu)(bu)開關(guan)噪(zao)聲(sheng)、非理(li)想(xiang)電源(yuan)(yuan)阻抗影響(xiang)、諧振及邊緣效應(ying)。一般情況下(xia)，同(tong)步(bu)(bu)開關(guan)噪(zao)聲(sheng)是電源(yuan)(yuan)噪(zao)聲(sheng)的(de)(de)(de)(de)主要來源(yuan)(yuan)。由于(yu)地(di)(di)引線和(he)平面(mian)存(cun)在(zai)(zai)寄生電感，在(zai)(zai)開關(guan)電流的(de)(de)(de)(de)作(zuo)用下(xia)，會(hui)造(zao)成(cheng)一定的(de)(de)(de)(de)電壓波(bo)(bo)動，也就是說，器(qi)件(jian)的(de)(de)(de)(de)參考(kao)地(di)(di)已不(bu)再是零電平，因(yin)此(ci)，驅動端要發(fa)送的(de)(de)(de)(de)地(di)(di)電平會(hui)出現相(xiang)(xiang)應(ying)的(de)(de)(de)(de)干(gan)(gan)擾波(bo)(bo)形(xing)(xing)，干(gan)(gan)擾波(bo)(bo)形(xing)(xing)的(de)(de)(de)(de)相(xiang)(xiang)位(wei)與地(di)(di)面(mian)噪(zao)聲(sheng)相(xiang)(xiang)同(tong)，對于(yu)開關(guan)信號波(bo)(bo)形(xing)(xing)來說，地(di)(di)噪(zao)聲(sheng)的(de)(de)(de)(de)影響(xiang)會(hui)導致信號的(de)(de)(de)(de)下(xia)降沿變(bian)緩；在(zai)(zai)接(jie)收端，信號的(de)(de)(de)(de)波(bo)(bo)形(xing)(xing)同(tong)樣會(hui)受到地(di)(di)噪(zao)聲(sheng)的(de)(de)(de)(de)干(gan)(gan)擾，但干(gan)(gan)擾波(bo)(bo)形(xing)(xing)的(de)(de)(de)(de)相(xiang)(xiang)位(wei)與地(di)(di)面(mian)噪(zao)聲(sheng)相(xiang)(xiang)反。另(ling)外，在(zai)(zai)一些存(cun)儲元器(qi)件(jian)中，有可能因(yin)為(wei)電源(yuan)(yuan)噪(zao)聲(sheng)和(he)地(di)(di)噪(zao)聲(sheng)造(zao)成(cheng)數(shu)據的(de)(de)(de)(de)意外翻(fan)轉。

在高頻(pin)電(dian)(dian)(dian)路中，電(dian)(dian)(dian)源(yuan)平面(mian)(mian)存在大量寄(ji)(ji)生(sheng)(sheng)參量，這些寄(ji)(ji)生(sheng)(sheng)參量可(ke)以看成是由很多(duo)電(dian)(dian)(dian)感(gan)(gan)和電(dian)(dian)(dian)容(rong)構成的(de)(de)LC諧(xie)振(zhen)(zhen)網絡(luo)，或諧(xie)振(zhen)(zhen)腔。在某一確定(ding)的(de)(de)頻(pin)率下，這些電(dian)(dian)(dian)容(rong)和電(dian)(dian)(dian)感(gan)(gan)將發生(sheng)(sheng)諧(xie)振(zhen)(zhen)現象(xiang)，從而影響電(dian)(dian)(dian)源(yuan)層(ceng)的(de)(de)阻抗。除了諧(xie)振(zhen)(zhen)效(xiao)應(ying)，電(dian)(dian)(dian)源(yuan)平面(mian)(mian)和地平面(mian)(mian)的(de)(de)邊(bian)(bian)緣效(xiao)應(ying)也是電(dian)(dian)(dian)源(yuan)設計中需要注(zhu)意的(de)(de)問題，這里(li)的(de)(de)邊(bian)(bian)緣效(xiao)應(ying)指邊(bian)(bian)緣反射和輻(fu)射現象(xiang)。電(dian)(dian)(dian)路板邊(bian)(bian)緣覆(fu)銅面(mian)(mian)大小受到(dao)限制，故容(rong)易產生(sheng)(sheng)電(dian)(dian)(dian)磁(ci)干(gan)擾問題。工程(cheng)中通常添加去耦電(dian)(dian)(dian)容(rong)，以減小邊(bian)(bian)緣的(de)(de)輻(fu)射效(xiao)應(ying)，達到(dao)抑制電(dian)(dian)(dian)源(yuan)平面(mian)(mian)噪(zao)聲的(de)(de)目的(de)(de)。

同步開關噪聲

同(tong)步開(kai)(kai)(kai)(kai)關(guan)噪(zao)聲（SSN）主要(yao)由伴隨著(zhu)器件(jian)(jian)的(de)(de)同(tong)步開(kai)(kai)(kai)(kai)關(guan)輸(shu)出產生(sheng)。開(kai)(kai)(kai)(kai)關(guan)速度(du)越(yue)(yue)快，瞬間電(dian)(dian)(dian)流(liu)變(bian)化越(yue)(yue)顯著(zhu)，電(dian)(dian)(dian)流(liu)回路上的(de)(de)電(dian)(dian)(dian)感越(yue)(yue)大(da)，則產生(sheng)的(de)(de)同(tong)步開(kai)(kai)(kai)(kai)關(guan)噪(zao)聲越(yue)(yue)嚴重。由此可(ke)見，同(tong)步開(kai)(kai)(kai)(kai)關(guan)噪(zao)聲的(de)(de)大(da)小取決于集(ji)成電(dian)(dian)(dian)路的(de)(de)I/O特性、PCB板電(dian)(dian)(dian)源(yuan)平(ping)面(mian)(mian)和(he)(he)地平(ping)面(mian)(mian)的(de)(de)阻抗，以及高速器件(jian)(jian)在(zai)PCB上的(de)(de)布局和(he)(he)布線方式。

根據(ju)回流(liu)(liu)路(lu)(lu)(lu)(lu)徑(jing)的(de)(de)(de)(de)不(bu)同(tong)，同(tong)步(bu)開(kai)(kai)(kai)(kai)關(guan)(guan)噪聲(sheng)可分為(wei)芯(xin)片(pian)外開(kai)(kai)(kai)(kai)關(guan)(guan)噪聲(sheng)和(he)(he)芯(xin)片(pian)內開(kai)(kai)(kai)(kai)關(guan)(guan)噪聲(sheng)。芯(xin)片(pian)外開(kai)(kai)(kai)(kai)關(guan)(guan)噪聲(sheng)是指(zhi)信(xin)號(hao)(hao)開(kai)(kai)(kai)(kai)關(guan)(guan)引發的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)(liu)回流(liu)(liu)經過(guo)信(xin)號(hao)(hao)線、電(dian)(dian)(dian)(dian)源/地(di)平面時產生的(de)(de)(de)(de)噪聲(sheng)；如(ru)果開(kai)(kai)(kai)(kai)關(guan)(guan)狀態轉變時，電(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)回流(liu)(liu)路(lu)(lu)(lu)(lu)徑(jing)經過(guo)電(dian)(dian)(dian)(dian)源和(he)(he)地(di)，而不(bu)是信(xin)號(hao)(hao)線，此時的(de)(de)(de)(de)噪聲(sheng)為(wei)芯(xin)片(pian)內開(kai)(kai)(kai)(kai)關(guan)(guan)噪聲(sheng)。減小(xiao)芯(xin)片(pian)內開(kai)(kai)(kai)(kai)關(guan)(guan)噪聲(sheng)主(zhu)要(yao)(yao)通(tong)(tong)過(guo)減小(xiao)開(kai)(kai)(kai)(kai)關(guan)(guan)信(xin)號(hao)(hao)流(liu)(liu)經路(lu)(lu)(lu)(lu)徑(jing)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)感(gan)或減緩開(kai)(kai)(kai)(kai)關(guan)(guan)信(xin)號(hao)(hao)的(de)(de)(de)(de)變化速率(lv)(lv)減小(xiao)感(gan)應電(dian)(dian)(dian)(dian)壓來實現。減小(xiao)芯(xin)片(pian)外開(kai)(kai)(kai)(kai)關(guan)(guan)噪聲(sheng)可以通(tong)(tong)過(guo)降低芯(xin)片(pian)內部(bu)驅動器的(de)(de)(de)(de)開(kai)(kai)(kai)(kai)關(guan)(guan)速率(lv)(lv)和(he)(he)同(tong)時開(kai)(kai)(kai)(kai)關(guan)(guan)的(de)(de)(de)(de)數目，采用(yong)能(neng)滿足時序要(yao)(yao)求(qiu)的(de)(de)(de)(de)最慢邊沿速率(lv)(lv)的(de)(de)(de)(de)芯(xin)片(pian)；或通(tong)(tong)過(guo)降低封(feng)裝回路(lu)(lu)(lu)(lu)電(dian)(dian)(dian)(dian)感(gan)，增加信(xin)號(hao)(hao)和(he)(he)電(dian)(dian)(dian)(dian)源與地(di)的(de)(de)(de)(de)耦合電(dian)(dian)(dian)(dian)感(gan)；也可在封(feng)裝內部(bu)使用(yong)旁路(lu)(lu)(lu)(lu)電(dian)(dian)(dian)(dian)容，讓電(dian)(dian)(dian)(dian)源和(he)(he)地(di)共同(tong)分擔(dan)電(dian)(dian)(dian)(dian)流(liu)(liu)回路(lu)(lu)(lu)(lu)，減小(xiao)回流(liu)(liu)路(lu)(lu)(lu)(lu)徑(jing)的(de)(de)(de)(de)等效(xiao)電(dian)(dian)(dian)(dian)感(gan)。

電源分配設計

電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)噪聲在(zai)(zai)很大(da)(da)程(cheng)度上源(yuan)(yuan)(yuan)(yuan)于非(fei)理想的(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)分配系(xi)統(tong)。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)分配系(xi)統(tong)就是給系(xi)統(tong)內的(de)(de)(de)(de)(de)(de)所有(you)器(qi)(qi)件(jian)提供足(zu)夠的(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)，這(zhe)些器(qi)(qi)件(jian)不但需要足(zu)夠的(de)(de)(de)(de)(de)(de)功率損耗，同(tong)時對(dui)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)的(de)(de)(de)(de)(de)(de)平(ping)穩性也(ye)有(you)一(yi)定的(de)(de)(de)(de)(de)(de)要求。因為(wei)(wei)實際電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)平(ping)面(mian)總存在(zai)(zai)著阻(zu)(zu)抗(kang)(kang)，在(zai)(zai)有(you)瞬間(jian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流通過時，就會產生(sheng)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)降，從而(er)導致電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)的(de)(de)(de)(de)(de)(de)波動(dong)。大(da)(da)部分器(qi)(qi)件(jian)對(dui)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)波動(dong)的(de)(de)(de)(de)(de)(de)要求在(zai)(zai)正(zheng)常電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)(de)(de)(de)(de)(de)±5%范圍內。為(wei)(wei)了(le)保證每個(ge)器(qi)(qi)件(jian)都能正(zheng)常工作，應(ying)該盡可能的(de)(de)(de)(de)(de)(de)降低(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)平(ping)面(mian)的(de)(de)(de)(de)(de)(de)阻(zu)(zu)抗(kang)(kang)。在(zai)(zai)工作頻率比較高的(de)(de)(de)(de)(de)(de)情況下，既(ji)要計(ji)算電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)的(de)(de)(de)(de)(de)(de)直流阻(zu)(zu)抗(kang)(kang)，還要計(ji)算由電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)引起的(de)(de)(de)(de)(de)(de)交流阻(zu)(zu)抗(kang)(kang)。在(zai)(zai)對(dui)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)阻(zu)(zu)抗(kang)(kang)進行控制時，可通過采(cai)用(yong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)率低(di)的(de)(de)(de)(de)(de)(de)材料，采(cai)用(yong)短而(er)粗厚的(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)線，減小(xiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)內阻(zu)(zu)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)盡量靠近(jin)地，使(shi)用(yong)去耦電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)等(deng)方(fang)法，以(yi)減小(xiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)的(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)，從而(er)降低(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)阻(zu)(zu)抗(kang)(kang)。