在PCB設計中(zhong)(zhong)，給(gei)信號(hao)(hao)提供一(yi)個(ge)穩定(ding)的(de)(de)(de)電(dian)壓以(yi)及合適的(de)(de)(de)電(dian)壓分(fen)配是電(dian)源(yuan)系(xi)統(tong)設計中(zhong)(zhong)的(de)(de)(de)兩(liang)個(ge)基(ji)本目標。隨著(zhu)信號(hao)(hao)完整(zheng)性(xing)問題的(de)(de)(de)出(chu)現，反射、串擾等都(dou)會影(ying)(ying)響(xiang)到電(dian)源(yuan)系(xi)統(tong)的(de)(de)(de)穩定(ding)，再(zai)加上芯片工作(zuo)電(dian)壓的(de)(de)(de)不斷減小(xiao)，電(dian)源(yuan)的(de)(de)(de)波動性(xing)將會影(ying)(ying)響(xiang)系(xi)統(tong)的(de)(de)(de)正常工作(zuo)。電(dian)源(yuan)完整(zheng)性(xing)分(fen)析，就是為了(le)保(bao)證PCB中(zhong)(zhong)有一(yi)個(ge)穩定(ding)可靠(kao)的(de)(de)(de)電(dian)源(yuan)供應。

電源完整性分析概述

電源(yuan)完整(zheng)性(xing)就(jiu)是指系統中電源(yuan)波形(xing)的(de)(de)(de)(de)質量。隨著IC輸(shu)出開關(guan)速(su)度的(de)(de)(de)(de)提高，信號的(de)(de)(de)(de)邊沿速(su)率(lv)即信號上(shang)升和下降的(de)(de)(de)(de)時(shi)間迅速(su)縮減，電源(yuan)線由于(yu)它的(de)(de)(de)(de)寄(ji)生(sheng)電感(gan)承受著不小的(de)(de)(de)(de)電壓(ya)降。對(dui)于(yu)小于(yu)1ns的(de)(de)(de)(de)信號邊沿速(su)率(lv)，會造成(cheng)PCB上(shang)電源(yuan)層與(yu)地層間的(de)(de)(de)(de)電壓(ya)在電路板的(de)(de)(de)(de)各(ge)處(chu)不同，從而影響到芯(xin)片供電的(de)(de)(de)(de)穩定(ding)性(xing)，甚至會導致芯(xin)片的(de)(de)(de)(de)邏輯(ji)

造(zao)(zao)(zao)成電(dian)源系統(tong)不穩定的(de)(de)(de)因素表現為(wei)同(tong)(tong)步開(kai)關(guan)噪(zao)(zao)聲、非理想(xiang)電(dian)源阻抗影響、諧(xie)振及邊緣效(xiao)應。一般(ban)情況下，同(tong)(tong)步開(kai)關(guan)噪(zao)(zao)聲是(shi)(shi)電(dian)源噪(zao)(zao)聲的(de)(de)(de)主要來源。由于(yu)地(di)(di)(di)引線和平面存在(zai)寄生電(dian)感，在(zai)開(kai)關(guan)電(dian)流的(de)(de)(de)作(zuo)用下，會(hui)造(zao)(zao)(zao)成一定的(de)(de)(de)電(dian)壓波(bo)動(dong)(dong)，也就是(shi)(shi)說，器件的(de)(de)(de)參考地(di)(di)(di)已不再是(shi)(shi)零(ling)電(dian)平，因此(ci)，驅動(dong)(dong)端(duan)要發送(song)的(de)(de)(de)地(di)(di)(di)電(dian)平會(hui)出現相(xiang)應的(de)(de)(de)干擾(rao)(rao)波(bo)形(xing)，干擾(rao)(rao)波(bo)形(xing)的(de)(de)(de)相(xiang)位與地(di)(di)(di)面噪(zao)(zao)聲相(xiang)同(tong)(tong)，對于(yu)開(kai)關(guan)信(xin)(xin)號(hao)波(bo)形(xing)來說，地(di)(di)(di)噪(zao)(zao)聲的(de)(de)(de)影響會(hui)導致信(xin)(xin)號(hao)的(de)(de)(de)下降沿(yan)變(bian)緩；在(zai)接收端(duan)，信(xin)(xin)號(hao)的(de)(de)(de)波(bo)形(xing)同(tong)(tong)樣會(hui)受到(dao)地(di)(di)(di)噪(zao)(zao)聲的(de)(de)(de)干擾(rao)(rao)，但干擾(rao)(rao)波(bo)形(xing)的(de)(de)(de)相(xiang)位與地(di)(di)(di)面噪(zao)(zao)聲相(xiang)反(fan)。另(ling)外，在(zai)一些存儲(chu)元(yuan)器件中，有可能因為(wei)電(dian)源噪(zao)(zao)聲和地(di)(di)(di)噪(zao)(zao)聲造(zao)(zao)(zao)成數據的(de)(de)(de)意(yi)外翻(fan)轉。

在(zai)高頻(pin)電(dian)(dian)(dian)(dian)(dian)路中，電(dian)(dian)(dian)(dian)(dian)源(yuan)平面(mian)存在(zai)大量(liang)寄生(sheng)(sheng)參(can)量(liang)，這些(xie)寄生(sheng)(sheng)參(can)量(liang)可(ke)以看(kan)成是(shi)由(you)很多電(dian)(dian)(dian)(dian)(dian)感和(he)(he)電(dian)(dian)(dian)(dian)(dian)容(rong)構成的(de)(de)(de)LC諧(xie)振(zhen)網絡，或諧(xie)振(zhen)腔(qiang)。在(zai)某一確(que)定的(de)(de)(de)頻(pin)率下(xia)，這些(xie)電(dian)(dian)(dian)(dian)(dian)容(rong)和(he)(he)電(dian)(dian)(dian)(dian)(dian)感將發(fa)生(sheng)(sheng)諧(xie)振(zhen)現象，從而影(ying)響(xiang)電(dian)(dian)(dian)(dian)(dian)源(yuan)層的(de)(de)(de)阻抗。除了諧(xie)振(zhen)效(xiao)應(ying)，電(dian)(dian)(dian)(dian)(dian)源(yuan)平面(mian)和(he)(he)地平面(mian)的(de)(de)(de)邊(bian)(bian)緣(yuan)(yuan)效(xiao)應(ying)也是(shi)電(dian)(dian)(dian)(dian)(dian)源(yuan)設計中需要注意的(de)(de)(de)問(wen)題，這里的(de)(de)(de)邊(bian)(bian)緣(yuan)(yuan)效(xiao)應(ying)指邊(bian)(bian)緣(yuan)(yuan)反射和(he)(he)輻射現象。電(dian)(dian)(dian)(dian)(dian)路板邊(bian)(bian)緣(yuan)(yuan)覆銅面(mian)大小(xiao)受到限(xian)制(zhi)，故容(rong)易產(chan)生(sheng)(sheng)電(dian)(dian)(dian)(dian)(dian)磁干擾問(wen)題。工程中通常添加去耦電(dian)(dian)(dian)(dian)(dian)容(rong)，以減小(xiao)邊(bian)(bian)緣(yuan)(yuan)的(de)(de)(de)輻射效(xiao)應(ying)，達到抑制(zhi)電(dian)(dian)(dian)(dian)(dian)源(yuan)平面(mian)噪聲的(de)(de)(de)目的(de)(de)(de)。

同步開關噪聲

同步開(kai)關(guan)(guan)噪聲（SSN）主(zhu)要由(you)伴隨著器件的(de)(de)同步開(kai)關(guan)(guan)輸出(chu)產生(sheng)。開(kai)關(guan)(guan)速度(du)越(yue)快，瞬間電流變(bian)化越(yue)顯著，電流回路上的(de)(de)電感越(yue)大，則產生(sheng)的(de)(de)同步開(kai)關(guan)(guan)噪聲越(yue)嚴重。由(you)此可見，同步開(kai)關(guan)(guan)噪聲的(de)(de)大小取決于集成電路的(de)(de)I/O特性、PCB板電源平面和(he)地平面的(de)(de)阻(zu)抗，以及(ji)高(gao)速器件在(zai)PCB上的(de)(de)布局(ju)和(he)布線方式。

根據回(hui)(hui)流(liu)路(lu)(lu)徑的(de)(de)不同(tong)，同(tong)步開(kai)(kai)(kai)關(guan)(guan)(guan)(guan)(guan)(guan)噪(zao)聲(sheng)(sheng)可分為芯片外(wai)開(kai)(kai)(kai)關(guan)(guan)(guan)(guan)(guan)(guan)噪(zao)聲(sheng)(sheng)和芯片內(nei)開(kai)(kai)(kai)關(guan)(guan)(guan)(guan)(guan)(guan)噪(zao)聲(sheng)(sheng)。芯片外(wai)開(kai)(kai)(kai)關(guan)(guan)(guan)(guan)(guan)(guan)噪(zao)聲(sheng)(sheng)是(shi)指信(xin)號開(kai)(kai)(kai)關(guan)(guan)(guan)(guan)(guan)(guan)引發的(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)回(hui)(hui)流(liu)經(jing)過(guo)信(xin)號線(xian)、電(dian)(dian)(dian)(dian)(dian)源(yuan)/地(di)平面時(shi)產生的(de)(de)噪(zao)聲(sheng)(sheng)；如果開(kai)(kai)(kai)關(guan)(guan)(guan)(guan)(guan)(guan)狀(zhuang)態轉變時(shi)，電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)回(hui)(hui)流(liu)路(lu)(lu)徑經(jing)過(guo)電(dian)(dian)(dian)(dian)(dian)源(yuan)和地(di)，而不是(shi)信(xin)號線(xian)，此時(shi)的(de)(de)噪(zao)聲(sheng)(sheng)為芯片內(nei)開(kai)(kai)(kai)關(guan)(guan)(guan)(guan)(guan)(guan)噪(zao)聲(sheng)(sheng)。減(jian)(jian)小(xiao)芯片內(nei)開(kai)(kai)(kai)關(guan)(guan)(guan)(guan)(guan)(guan)噪(zao)聲(sheng)(sheng)主要通過(guo)減(jian)(jian)小(xiao)開(kai)(kai)(kai)關(guan)(guan)(guan)(guan)(guan)(guan)信(xin)號流(liu)經(jing)路(lu)(lu)徑的(de)(de)電(dian)(dian)(dian)(dian)(dian)感(gan)或(huo)減(jian)(jian)緩開(kai)(kai)(kai)關(guan)(guan)(guan)(guan)(guan)(guan)信(xin)號的(de)(de)變化速率(lv)減(jian)(jian)小(xiao)感(gan)應電(dian)(dian)(dian)(dian)(dian)壓來實現。減(jian)(jian)小(xiao)芯片外(wai)開(kai)(kai)(kai)關(guan)(guan)(guan)(guan)(guan)(guan)噪(zao)聲(sheng)(sheng)可以通過(guo)降(jiang)低芯片內(nei)部(bu)驅動器(qi)的(de)(de)開(kai)(kai)(kai)關(guan)(guan)(guan)(guan)(guan)(guan)速率(lv)和同(tong)時(shi)開(kai)(kai)(kai)關(guan)(guan)(guan)(guan)(guan)(guan)的(de)(de)數目，采(cai)用能滿足時(shi)序要求的(de)(de)最慢邊沿速率(lv)的(de)(de)芯片；或(huo)通過(guo)降(jiang)低封裝回(hui)(hui)路(lu)(lu)電(dian)(dian)(dian)(dian)(dian)感(gan)，增(zeng)加信(xin)號和電(dian)(dian)(dian)(dian)(dian)源(yuan)與地(di)的(de)(de)耦合電(dian)(dian)(dian)(dian)(dian)感(gan)；也可在封裝內(nei)部(bu)使用旁路(lu)(lu)電(dian)(dian)(dian)(dian)(dian)容(rong)，讓電(dian)(dian)(dian)(dian)(dian)源(yuan)和地(di)共同(tong)分擔(dan)電(dian)(dian)(dian)(dian)(dian)流(liu)回(hui)(hui)路(lu)(lu)，減(jian)(jian)小(xiao)回(hui)(hui)流(liu)路(lu)(lu)徑的(de)(de)等效電(dian)(dian)(dian)(dian)(dian)感(gan)。

電源分配設計

電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)噪聲在(zai)很大(da)(da)程(cheng)度上源(yuan)于(yu)非理(li)想的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)分配系統。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)分配系統就是給系統內(nei)的(de)(de)(de)所有器件(jian)提供(gong)足夠的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)，這些(xie)器件(jian)不但需(xu)要(yao)(yao)足夠的(de)(de)(de)功率損耗，同時對(dui)(dui)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)平(ping)穩性(xing)也(ye)有一(yi)定(ding)的(de)(de)(de)要(yao)(yao)求(qiu)。因為(wei)實際電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)平(ping)面總存在(zai)著阻(zu)(zu)抗，在(zai)有瞬間(jian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)通過時，就會產生電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)降(jiang)，從(cong)而(er)導致電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)波動。大(da)(da)部分器件(jian)對(dui)(dui)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)波動的(de)(de)(de)要(yao)(yao)求(qiu)在(zai)正常(chang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)(de)(de)±5%范圍內(nei)。為(wei)了保證每個器件(jian)都(dou)能(neng)正常(chang)工作(zuo)，應該盡(jin)(jin)可能(neng)的(de)(de)(de)降(jiang)低(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)平(ping)面的(de)(de)(de)阻(zu)(zu)抗。在(zai)工作(zuo)頻率比較(jiao)高(gao)的(de)(de)(de)情況(kuang)下，既(ji)要(yao)(yao)計算電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)的(de)(de)(de)直流(liu)(liu)阻(zu)(zu)抗，還要(yao)(yao)計算由電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)感引起的(de)(de)(de)交(jiao)流(liu)(liu)阻(zu)(zu)抗。在(zai)對(dui)(dui)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)阻(zu)(zu)抗進行(xing)控制時，可通過采(cai)用電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)率低(di)的(de)(de)(de)材料，采(cai)用短而(er)粗厚的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)線，減小(xiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)內(nei)阻(zu)(zu)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)盡(jin)(jin)量靠近(jin)地，使用去耦(ou)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容等方法，以減小(xiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)感，從(cong)而(er)降(jiang)低(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)阻(zu)(zu)抗。