流(liu)經(jing)所(suo)布(bu)線(xian)路(lu)的(de)所(suo)有(you)電(dian)流(liu)都(dou)有(you)相(xiang)等(deng)的(de)回(hui)流(liu)。耦(ou)合(he)策(ce)略(lve)固(gu)然(ran)很(hen)多(duo)
，不(bu)過(guo)回(hui)流(liu)通(tong)常(chang)流(liu)經(jing)相(xiang)鄰(lin)的(de)接(jie)地(di)層(ceng)或(huo)與(yu)信(xin)號(hao)線(xian)路(lu)並(bing)行(xing)布(bu)置(zhi)的(de)接(jie)地(di)。在(zai)參(can)考(kao)層(ceng)繼(ji)續(xu)時(shi)，所(suo)有(you)耦(ou)合(he)都(dou)僅(jin)限(xian)於(yu)傳(chuan)輸(shu)線(xian)路(lu)，一(yi)切(qie)都(dou)非(fei)常(chang)正(zheng)常(chang)。不(bu)過(guo)，如(ru)果(guo)信(xin)號(hao)線(xian)路(lu)從(cong)頂(ding)層(ceng)切(qie)換(huan)至(zhi)內(nei)部(bu)或(huo)底(di)層(ceng)時(shi)
，回(hui)流(liu)也(ye)必(bi)須(xu)獲(huo)得(de)路(lu)徑(jing)。

 

圖1就(jiu)是(shi)一(yi)個(ge)實(shi)例(li)。頂(ding)層(ceng)信(xin)號(hao)線(xian)路(lu)電(dian)流(liu)下(xia)麵(mian)緊(jin)挨(ai)著(zhe)就(jiu)是(shi)回(hui)流(liu)。當(dang)它(ta)轉(zhuan)移(yi)到(dao)底(di)層(ceng)時(shi)，回(hui)流(liu)就(jiu)通(tong)過(guo)附(fu)近(jin)的(de)通(tong)孔(kong)。不(bu)過(guo)，如(ru)果(guo)附(fu)近(jin)沒(mei)有(you)用(yong)於(yu)回(hui)流(liu)的(de)通(tong)孔(kong)時(shi)
，回(hui)流(liu)就(jiu)要(yao)通(tong)過(guo)最(zui)近(jin)可(ke)用(yong)的(de)接(jie)地(di)通(tong)孔(kong)。更(geng)遠(yuan)的(de)距(ju)離(li)會(hui)產(chan)生(sheng)電(dian)流(liu)環(huan)路(lu)，形(xing)成(cheng)電(dian)感(gan)器(qi)。如(ru)果(guo)這(zhe)種(zhong)不(bu)必(bi)要(yao)的(de)電(dian)流(liu)路(lu)徑(jing)偏(pian)移(yi)
，碰(peng)巧(qiao)又(you)同(tong)另(ling)一(yi)條(tiao)線(xian)路(lu)交(jiao)叉(cha)，那(na)麼(me)幹(gan)擾(rao)就(jiu)會(hui)更(geng)嚴(yan)重(zhong)。這(zhe)種(zhong)電(dian)流(liu)環(huan)路(lu)其(qi)實(shi)相(xiang)當(dang)於(yu)形(xing)成(cheng)了(le)一(yi)個(ge)天(tian)線(xian)！

 

圖1：信號電流從器件引腳經過通孔流到較低層。

 

回流在被迫流向最近通孔改變至不同參考層之前位於信號之下。

 

jiedicankaoshizuijiacelve
，dangaosuxianluyoushihoukebuzhizaineibucengshang。jiedicankaocengshangxiadoufangzhifeichangkunnan
，bandaotichangshangkenenghuishoudaoyinjiaoxianzhi
，badianyuanxiananfangzaigaosuxianlupangbian。cankaodianliuyaoshixuyaozaifeiDC耦合的各層或各網之間切換
，應緊挨著開關點安放去耦電容。

 

 

許多器件在器件封裝底部都采用散熱接地焊盤。在RF器qi件jian上shang，這zhe些xie通tong常chang都dou是shi電dian氣qi接jie地di，而er相xiang鄰lin焊han盤pan點dian有you接jie地di通tong孔kong陣zhen列lie。可ke將jiang器qi件jian焊han盤pan直zhi接jie連lian接jie至zhi接jie地di引yin腳jiao
，並bing通tong過guo頂ding層ceng接jie地di連lian接jie至zhi任ren何he灌guan銅tong。如ru有you多duo個ge路lu徑jing，回hui流liu會hui按an路lu徑jing阻zu抗kang比bi例li拆chai分fen。通tong過guo焊han盤pan進jin行xing接jie地di連lian接jie相xiang對dui於yu引yin腳jiao接jie地di而er言yan，路lu徑jing更geng短duan

、阻抗更低。

 

dianlubanyuqijianhanpanzhijianlianghaodedianqilianjiezhiguanzhongyao。zhuangpeishi

，dianlubantongkongzhenliezhongdeweitianchongtongkongyekenenghuichouzouqijiandehangao，liuxiakongxi。tianmantongkongshibaozhenghanjiedaoweidehaobanfa。zaipingcezhong
，haiyaodakaihanjieyanmocengquerenmeiyouhanjieyanmozaiqijianxiafangdedianlubanjiedishang，yinweihanjieyanmokenenghuitaigaoqijianhuoshiqiyaobai。

 

 

qijianzhoubiandaochudoushitongkong。dianyuanwangfenjiechengbendiquou，ranhoujiangzhidianyuanceng，tongchangtigongduogetongkongyizuidaxiandujianshaodiangan
，tigaozailiurongliang，tongshikongzhizongxiankejiangzhineiceng。suoyouzhexiefenjiezuizhongdouhuizaiqijianfujinwanquanbeiqianzhu。

 

meigezhexietongkongdouhuizaineijiedicengshangchanshengdayutongkongzhijingzishendejinruqu，tigongzhizaokongxi。zhexiejinruquhenrongyizaihuiliulujingshangzaochengzhongduan。yixietongkongbicikaojinzehuixingchengjiedicenggou
，dingcengCAD視圖看不見，這將導致情況進一步複雜化。圖2兩liang個ge電dian源yuan層ceng通tong孔kong的de接jie地di層ceng空kong隙xi可ke產chan生sheng重zhong疊die的de禁jin入ru區qu，並bing在zai返fan回hui路lu徑jing上shang造zao成cheng中zhong斷duan。回hui流liu隻zhi能neng轉zhuan道dao繞rao過guo接jie地di層ceng禁jin入ru區qu，形xing成cheng現xian在zai常chang見jian的de發fa射she感gan應ying路lu徑jing問wen題ti。

 

圖2：通孔周圍接地層的禁入區可能重疊，迫使回流遠離信號路徑。

 

即便沒有重疊，禁入區也會在接地層形成鼠咬阻抗中斷。

 

甚至“友好型”jieditongkongyehuiweixiangguanjinshuhanpandailaidianlubanzhizaogongyiyaoqiudezuixiaochicunguige。tongkongruguofeichangkaojinxinhaoxianlu，jiuhuichanshenghaoxiangdingcengjiedikongxibeilaoshuyaodiaoyikuaiyiyangdeqinshi。tu2是鼠咬示意圖。

 

由於禁入區由CAD軟ruan件jian自zi動dong生sheng成cheng，通tong孔kong在zai係xi統tong電dian路lu板ban上shang的de使shi用yong又you很hen頻pin繁fan


，因yin此ci先xian期qi布bu局ju過guo程cheng幾ji乎hu總zong會hui出chu現xian一yi些xie返fan回hui路lu徑jing中zhong斷duan問wen題ti。布bu局ju評ping測ce時shi要yao跟gen蹤zong每mei條tiao高gao速su線xian路lu，檢jian查zha相xiang關guan回hui流liu層ceng以yi避bi免mian中zhong斷duan。讓rang所suo有you可ke在zai任ren何he區qu域yu產chan生sheng接jie地di層ceng幹gan擾rao的de通tong孔kong更geng靠kao近jin頂ding層ceng接jie地di空kong隙xi是shi一yi個ge不bu錯cuo的de方fang法fa。

 

 

huiliulujingduixinhaoxianluxingnengzhiguanzhongyao，qiyingshiweixinhaolujingdeyibufen。yucitongshi，chafenduitongchangmeiyoujinmiouhe，huiliukenengliujingxianglinceng。lianggehuiliubixutongguoxiangdengdedianqilujingbuxian。

 

即ji便bian在zai差cha分fen對dui的de兩liang條tiao線xian路lu不bu緊jin密mi耦ou合he時shi，鄰lin近jin與yu共gong享xiang型xing設she計ji限xian製zhi也ye會hui讓rang回hui流liu處chu於yu相xiang同tong層ceng。要yao真zhen正zheng保bao持chi低di寄ji生sheng信xin號hao，需xu要yao更geng好hao的de匹pi配pei。差cha分fen組zu件jian下xia接jie地di層ceng的de斷duan流liu器qi等deng任ren何he計ji劃hua結jie構gou都dou應ying是shi對dui稱cheng的de。同tong樣yang，長chang度du是shi否fou匹pi配pei可ke能neng也ye會hui產chan生sheng信xin號hao線xian路lu中zhong的de波bo形xing曲qu線xian問wen題ti。回hui流liu不bu會hui引yin起qi波bo形xing曲qu線xian問wen題ti。一yi條tiao差cha分fen線xian路lu的de長chang度du匹pi配pei情qing況kuang應ying在zai其qi它ta差cha分fen線xian路lu中zhong體ti現xian。

 

 

時鍾和控製線路有時可視為沒什麼影響的鄰居
，因為其工作速度低
，甚至接近DC。buguo
，qikaiguantexingjihujiejinfangbo，kezaiqishuxiebopinlvxiashengchengdutedeyintiao。fangbofashenengyuandejibenpinlvsuiranbuhuichanshengshenmeyingxiang
，danqiruilidebianyuankenenghuiyouyingxiang。zaishuzixitongshejizhong，zhuanzhepinlvkegusuanbixuyaokaolvdezuigaopinlvxiebo，jisuanfangshiwei：Fknee=0.5/Tr，這裏的Tr是shi上shang升sheng時shi間jian。請qing注zhu意yi，是shi上shang升sheng時shi間jian
，而er不bu是shi信xin號hao頻pin率lv。不bu過guo銳rui利li邊bian緣yuan的de方fang波bo也ye有you強qiang大da的de高gao階jie奇qi數shu諧xie波bo，其qi可ke能neng隻zhi在zai錯cuo誤wu頻pin率lv下xia下xia降jiang並bing耦ou合he在zaiRF線路上
，違反嚴格的傳輸掩模要求。

 

時鍾和控製線路應由內部接地層或頂層接地灌流（ground pour）與RFxinhaoxianlugeli。ruguobunengshiyongjiedigelixinhao，namexianlubuxianyingquebaozhijiaojiaocha。yinweishizhonghuokongzhixianlufashedecitongxianluhuiweiraoganraoyuanxianludedianliuxingchengfangshezhuxingdenggaoxian，tamenjiangbuhuizaijieshouqixianluzhongchanshengdianliu。fangmanshangshengshijianbudankejiangdizhuanzhepinlv，erqiehaiyouzhuyujianshaoganraoyuandeganrao，danshizhonghuokongzhixianluyekechongdangjieshouqixianlu。jieshouqixianlurengkezuoweijiangjishengxinhaodaoruqijiandedaoguan。

 

 

微(wei)波(bo)傳(chuan)輸(shu)帶(dai)與(yu)帶(dai)線(xian)大(da)多(duo)數(shu)都(dou)與(yu)相(xiang)鄰(lin)接(jie)地(di)層(ceng)耦(ou)合(he)。一(yi)些(xie)通(tong)量(liang)線(xian)路(lu)仍(reng)沿(yan)水(shui)平(ping)方(fang)向(xiang)散(san)發(fa)，並(bing)端(duan)接(jie)於(yu)相(xiang)鄰(lin)跡(ji)線(xian)。一(yi)條(tiao)高(gao)速(su)線(xian)路(lu)或(huo)差(cha)分(fen)對(dui)上(shang)的(de)音(yin)調(tiao)在(zai)下(xia)一(yi)條(tiao)跡(ji)線(xian)上(shang)終(zhong)結(jie)
，但(dan)信(xin)號(hao)層(ceng)上(shang)的(de)接(jie)地(di)灌(guan)流(liu)會(hui)為(wei)通(tong)量(liang)線(xian)路(lu)帶(dai)來(lai)較(jiao)低(di)阻(zu)抗(kang)的(de)終(zhong)點(dian)
，讓(rang)鄰(lin)近(jin)跡(ji)線(xian)不(bu)受(shou)音(yin)調(tiao)幹(gan)擾(rao)。

 

時鍾分布或合成器設備路由出來、yongyuchengzaixiangtongpinlvdejixianjiqunkenengxianglinerxing，yinweiganraoyuanyintiaoyijingcunzaiyujieshouqixianlushang。buguo，fenzudexianluzuizhonghuifensan。fensanshi，yingzaifensanxianluzhijiantigongjiediguanliu，bingzaiqikaishifensandedifangguanrutongkong
，yibianganyinghuiliuyanzheedinghuiliulujingliuhui。zaitu3zhong，jiedidaomoduandetongkongkeshiganyingdianliuliudaocankaocengshang。jiediguanliushangqitatongkongzhijiandejiangebuyaochaoguoyigebochangdeshifenzhiyi，yiquebaojiedibuhuichengweigongzhenjiegou。

 

圖3：差分線路分散處的頂層接地通孔為回流提供流動路徑。

 

 

音調進入電源層就會擴散到每個地方。如果雜散音調進入電源、緩衝器、混頻器、衰減器和振蕩器，就會對幹擾頻率進行調製。同樣，當電源到達電路板時，它還沒有徹底被清空而實現對RF電路係統的驅動。應最大限度減少RF線路在電源層的暴露，特別是未過濾的電源層。

 

鄰近接地的大型電源層可創建高質量嵌入式電容，使寄生信號衰減
，並用於數字通信係統與某些RF係統。另一種方法是使用最小化電源層，有時更像是肥大跡線而不能說是層
，這樣RF線路更容易徹底避開電源層。這兩種方法都可行

，不過決不能將二者的最差特性湊在一起，也就是既使用小型電源層，又在頂部走線RF線路。

 

 

quoubujinyouzhuyubimianzasanzaoshengjinruqijian，haikebangzhuxiaochuqijianneibushengchengdeyintiao，bimianqiouhedaodianyuancengshang。quoudianrongyuekaojingongzuodianluxitong，xiaolvjiuyuegao。bendiquoushoudianlubanjixiandejishengzukangganraojiaoxiao，jiaoduandejixianzhichijiaoxiaodetianxian
，jianshaoyouhaiyintiaofashe。dianrongqianfangyaojiehezuigaozigongzhenpinlv，tongchangzuixiaozhi、最小外殼尺寸
、最靠近器件
，以及越大的電容器

，離器件越遠。在RF頻率下，電路板背麵的電容器會產生通孔串連接地路徑的寄生電感
，損失大量噪聲衰減優勢。

 

 

通過電路板布局評測
，我們可發現可能發射或接收雜散RF音yin調tiao的de結jie構gou。要yao跟gen蹤zong每mei一yi條tiao線xian路lu，有you意yi識shi地di明ming確que其qi回hui流liu路lu徑jing，確que保bao它ta能neng夠gou與yu線xian路lu並bing行xing，特te別bie是shi要yao徹che底di檢jian查zha過guo渡du。此ci外wai，還hai要yao將jiang潛qian在zai幹gan擾rao源yuan與yu接jie收shou器qi隔ge離li。按an照zhao一yi些xie簡jian單dan直zhi觀guan的de規gui則ze降jiang低di寄ji生sheng信xin號hao
，可ke加jia速su產chan品pin發fa布bu
，降jiang低di調tiao試shi成cheng本ben。