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單片機系統的電磁兼容性設計

隨著單片機系統越來越廣泛地應用于消費類電子、醫療、工業自動化、智能化儀器儀表、航空航天等各領域,單片機系統面臨著電磁干擾(EMI)日益嚴重的威脅。電磁兼容性(EMC)包含系統的發射和敏感度兩方面的問題。如果一個單片機系統符合下面三個條件,則該系統是電磁兼容的:

① DUIQITAXITONGBUCHANSHENGGANRAO;

② DUIQITAXITONGDEFASHEBUMINGAN;

③ DUIXITONGBENSHENBUCHANSHENGGANRAO;

     假若干擾不能完全消除,但也要使干擾減少到最小。干擾的產生不是直接的(通過導體、公共阻抗耦合等),就是間接的(通過串擾或輻射耦合)。電磁干擾的產生是通過導體和通過輻射,很多電磁發射源,如光照、繼電器、DC電機和日光燈都可引起干擾;AC電源線、互連電纜、金屬電纜和子系統的內部電路也都可能產生輻射或接收到不希望的信號。在高速單片機系統中,時鐘電路通常是寬帶噪聲的最大產生源,這些電路可產生高達300MHz的諧波失真,在系統中應該把它們去掉。另外,在單片機系統中,最容易受影響的是復位線、中斷線和控制線。

1 GANRAODEOUHEFANGSHI

AG体育 (1)CHUANDAOXINGEMI

       YIZHONGZUIMINGXIANERWANGWANGBEIHULVEDENENGYINQIDIANLUZHONGZAOSHENGDELUJINGSHIJINGGUODAOTI。YITIAOCHUANGUOZAOSHENGHUANJINGDEDAOXIANKEJIANSHIZAOSHENGBINGBAZAOSHENGSONGDAOQITADIANLUYINQIGANRAO。SHEJIRENYUANBIXUBIMIANDAOXIANJIANSHIZAOSHENGHEZAIZAOSHENGYINQIGANRAOQIAN,YONGQUOUBANFACHUQUZAOSHENG。ZUIPUTONGDELIZISHIZAOSHENGTONGGUODIANYUANXIANJINRUDIANLU。RUODIANYUANBENSHENHUOLIANJIEDAODIANYUANDEQITADIANLUSHIGANRAOYUAN,ZEZAIDIANYUANXIANJINRUDIANLUZHIQIANBIXUDUIQIQUOU。

(2)GONGGONGZUKANGOUHE

AG体育       DANGLAIZILIANGGEBUTONGDIANLUDEDIANLIULIUJINGYIGEGONGGONGZUKANGSHIJIUHUICHANSHENGGONGZUKANGOUHE。ZUKANGSHANGDEYAJIANGYOULIANGGEDIANLUJUEDING,LAIZILIANGGEDIANLUDEDIDIANLIULIUJINGGONGDIZUKANG。DIANLU1DEDIDIANWEIBEIDIDIANLIU2DIAOZHI,ZAOSHENGXINHAOHUODCBUCHANGJINGGONGDIZUKANGCONGDIANLU2OUHEDAODIANLU1。

(3)FUSHEOUHE

AG体育 JINGFUSHEDEOUHETONGCHENGCHUANRAO。CHUANRAOFASHENGZAIDIANLIULIUJINGDAOTISHICHANSHENGDIANCICHANG,ERDIANCICHANGZAILINJINDEDAOTIZHONGGANYINGSHUNTAIDIANLIU。

(4)FUSHEFASHE

AG体育      FUSHEFASHEYOULIANGZHONGJIBENLEIXING:CHAFENMOSHI(DM)HEGONGMO(CM)。GONGMOFUSHEHUODANJITIANXIANFUSHESHIYOUWUYIDEYAJIANGYINQIDE,TASHIDIANLUZHONGSUOYOUDILIANJIETAIGAODAOXITONGDIDIANWEIZHISHANG。JIUDIANCHANGDAXIAOERYAN,CMFUSHESHIBIDMFUSHEGENGWEIYANZHONGDEWENTI。WEISHICMFUSHEZUIXIAO,BIXUYONGQIEHESHIJIDESHEJISHIGONGMODIANLIUJIANGDAOLING。

 2 YINGXIANGEMCDEYINSHU

AG体育 ①DIANYA。DIANYUANDIANYAYUEGAO,YIWEIZHUDIANYAZHENFUYUEDA,FASHEJIUGENGDUO,ERDIDIANYUANDIANYAYINGXIANGMINGANDU。

② 頻率。高頻產生更多的發射,周期性信號產生更多的發射。在高頻單片機AG体育系統中,當器件開關時產生電流尖峰信號;在模擬系統中,當負載電流變化時產生電流尖峰信號。

③ JIEDI。ZAISUOYOUEMCWENTIZHONG,ZHUYAOWENTISHIBUSHIDANGDEJIEDIYINQIDE。YOUSANZHONGXINHAOJIEDIFANGFA:DANDIAN、DUODIANHEHUNHE。ZAIPINLVDIYU1 MHzSHI,KECAIYONGDANDIANJIEDIFANGFA,DANBUSHIYUGAOPIN;ZAIGAOPINYINGYONGZHONG,ZUIHAOCAIYONGDUODIANJIEDI。HUNHEJIEDISHIDIPINYONGDANDIANJIEDI,ERGAOPINYONGDUODIANJIEDIDEFANGFA。DIXIANBUJUSHIGUANJIAN,GAOPINSHUZIDIANLUHEDIDIANPINGMONIDIANLUDEDIHUILUJUEDUIBUNENGHUNHE。

 

④PCBSHEJI。SHIDANGDEYINSHUADIANLUBAN(PCB)BUXIANDUIFANGZHIEMISHIZHIGUANZHONGYAODE。

AG体育  ⑤ DIANYUANQUOU。DANGQIJIANKAIGUANSHI,ZAIDIANYUANXIANSHANGHUICHANSHENGSHUNTAIDIANLIU,BIXUSHUAIJIANHELVDIAOZHEXIESHUNTAIDIANLIU。LAIZIGAOdi/dtYUANDESHUNTAIDIANLIUDAOZHIDIHEXIANJI“FASHE”DIANYA,GAOdi/dtCHANSHENGDAFANWEIGAOPINDIANLIU,JILIBUJIANHEXIANLANFUSHE。LIUJINGDAOXIANDEDIANLIUBIANHUAHEDIANGANHUIDAOZHIYAJIANG,JIANXIAODIANGANHUODIANLIUSUISHIJIANDEBIANHUAKESHIGAIYAJIANGZUIXIAO。

3 YINSHUADIANLUBAN(PCB)DEDIANCIJIANRONGXINGSHEJI

PCB是單片機系統中電路元件和器件的支撐件,它提供電路元件和器件之間的電氣連接。隨著電子技術的飛速發展,PCB的密度越來越高。PCB設計的好壞對單片機系統的電磁兼容性影響很大,實踐證明,即使電路原理圖設計正確,印刷電路板設計不當,也會對單片機系統的可靠性產生不利影響。例如,如果印刷板兩條細平行線靠得很近,則會形成信號波形的延遲,在傳輸線的終端形成反射噪聲。因此,在設計印刷電路板的時候,應注意采用正確的方法,遵守PCB設計的一般原則,并應符合抗干擾設計的要求。

3.1 PCBSHEJIDEYIBANYUANZE

  YAOSHIDIANZIDIANLUHUODEZUIJIAXINGNENG,YUANQIJIANDEBUJUJIDAOXIANDEBUSHESHIHENZHONGYAODE。WEILESHEJIZHILIANGHAO、CHENGBENDIDEPCB,YINGZUNXUNYIXIAYIBANXINGYUANZE。

 (1)TESHUYUANQIJIANBUJU

   SHOUXIAN,YAOKAOLVPCBCHICUNDEDAXIAO:PCBCHICUNGUODASHI,YINSHUAXIANTIAOCHANG,ZUKANGZENGJIA,KANGZAOSHENGNENGLIXIAJIANG,CHENGBENYEZENGJIA;GUOXIAO,ZESANREBUHAO,QIELINJINXIANTIAOYISHOUGANRAO。ZAIQUEDINGPCBCHICUNHOU,ZAIQUEDINGTESHUYUANQIJIANDEWEIZHI。ZUIHOU,GENJUDIANLUDEGONGNENGDANYUAN,DUIDIANLUDEQUANBUYUANQIJIANJINXINGBUJU。

AG体育 ZAIQUEDINGTESHUYUANQIJIANDEWEIZHISHIYAOZUNSHOUYIXIAYUANZE:

① JINKENENGSUODUANGAOPINYUANQIJIANZHIJIANDELIANXIAN,SHEFAJIANSHAOTAMENDEFENBUCANSHUHEXIANGHUJIANDEDIANCIGANRAO。YISHOUGANRAODEYUANQIJIANBUNENGXIANGHUAIDETAIJIN,SHURUHESHUCHUYUANJIANYINGJINLIANGYUANLI。

② MOUXIEYUANQIJIANHUODAOXIANZHIJIANKENENGYOUJIAOGAODEDIANWEICHA,YINGJIADATAMENZHIJIANDEJULI,YIMIANFANGDIANYINCHUYIWAIDUANLU。DAIGAODIANYADEYUANQIJIANYINGJINLIANGBUZHIZAIDIAOSHISHISHOUBUYICHUJIDEDIFANG。

③ ZHONGLIANGCHAOGUO15 gDEYUANQIJIAN,YINGDANGYONGZHIJIAJIAYIGUDING,RANHOUHANJIE。NEIXIEYOUDAYOUZHONG、FARELIANGDUODEYUANQIJIAN,BUYIZHUANGZAIYINSHUABANSHANG,ERYINGZHUANGZAIZHENGJIDEJIXIANGDIBANSHANG,QIEYINGKAOLVSANREWENTI。REMINYUANJIANYINGYUANLIFAREYUANJIAN。

AG体育 ④DUIYUDIANWEIQI、KEDIAODIANGANXIANQUAN、KEBIANDIANRONGQI、WEIDONGKAIGUANDENGKEDIAOYUANJIANDEBUJU,YINGKAOLVZHENGJIDEJIEGOUYAOQIU。RUOSHIJINEIDIAOJIE,YINGFANGZAIYINSHUABANSHANGFANGBIANDIAOJIEDEDIFANG;RUOSHIJIWAIDIAOJIE,QIWEIZHIYAOYUDIAOJIEXUANNIUZAIJIXIANGMIANBANSHANGDEWEIZHIXIANGSHIYING。

AG体育 ⑤ LIUCHUYINSHUABANDINGWEIKONGJIGUDINGZHIJIASUOZHANYONGDEWEIZHI。

(2)YIBANYUANQIJIANBUJU

GENJUDIANLUDEGONGNENGDANYUAN,DUIDIANLUDEQUANBUYUANQIJIANJINXINGBUJUSHI,YAOFUHEYIXIAYUANZE:

AG体育 ① ANZHAODIANLUDELIUCHENGANPAIGEGEGONGNENGDIANLUDANYUANDEWEIZHI,SHIBUJUBIANYUXINHAOLIUTONG,BINGSHIXINHAOJINKENENGBAOCHIYIZHIDEFANGXIANG。

AG体育 ② YIMEIGEGONGNENGDIANLUDEHEXINYUANJIANWEIZHONGXIN,WEIRAOTALAIJINXINGBUJU。YUANQIJIANYINGJUNYUN、ZHENGQI、JINCOUDIPAILIEZAIPCBSHANG,JINLIANGJIANSHAOHESUODUANGEYUANQIJIANZHIJIANDEYINXIANHELIANJIE。

③ZAIGAOPINXIAGONGZUODEDIANLU,YAOKAOLVYUANQIJIANZHIJIANDEFENBUCANSHU。YIBANDIANLUYINGJINKENENGSHIYUANQIJIANPINGXINGPAILIE,ZHEYANG,BUDANMEIGUAN,ERQIEZHUANGHANRONGYI,YIYUPILIANGSHENGCHAN。

AG体育 ④ WEIYUDIANLUBANBIANYUANDEYUANQIJIAN,LIDIANLUBANBIANYUANYIBANBUXIAOYU2mm。DIANLUBANDEZUIJIAXINGZHUANGWEIJUXING。CHANGKUANBIWEI3:2HUO4:3。DIANLUBANMIANCHICUNDAYU200 mm×150 mmSHI,YINGKAOLVDIANLUBANSUOSHOUDEJIXIEQIANGDU。

 (3)BUXIAN

BUXIANDEYUANZERUXIA:

① SHURUSHUCHUDUANYONGDEDAOXIANYINGJINLIANGBIMIANXIANGLINPINGXING,ZUIHAOJIAXIANJIANDIXIAN,YIMIANFASHENGFANKUIOUHE。

② YINSHUABANDAOXIANDEZUIXIAOKUANDUZHUYAOYOUDAOXIANYUJUEYUANJIBANJIANDEZHANFUQIANGDUHELIUGUOTAMENDEDIANLIUZHIJUEDING。DANGTONGBOHOUDUWEI0.5mm、KUANDUWEI1~15 mmSHI,TONGGUO2 ADEDIANLIU,WENSHENGBUHUIGAOYU3℃。YINCI,DAOXIANKUANDUWEI1.5mmKEMANZUYAOQIU。DUIYUJICHENGDIANLU,YOUQISHISHUZIDIANLU,TONGCHANGXUAN0.2~0.3 mmDAOXIANKUANDU。DANGRAN,ZHIYAOYUNXU,HUANSHIJINKENENGYONGKUANXIAN,YOUQISHIDIANYUANXIANHEDIXIAN。DAOXIANDEZUIXIAOJIANJUZHUYAOYOUZUIHUAIQINGKUANGXIADEXIANJIANJUEYUANDIANZUHEJICHUANDIANYAJUEDING。DUIYUJICHENGDIANLU,YOUQISHISHUZIDIANLU,ZHIYAOGONGYIYUNXU,KESHIJIANJUXIAOYU0.1~0.2mm。

③ YINSHUADAOXIANGUAIWANCHUYIBANQUYUANHUXING,ERZHIJIAOHUOJIAJIAOZAIGAOPINDIANLUZHONGHUIYINGXIANGDIANQIXINGNENG。CIWAI,JINLIANGBIMIANSHIYONGDAMIANJITONGBO,FOUZE,CHANGSHIJIANSHOURESHI,YIFASHENGTONGBOPENGZHANGHETUOLUOXIANXIANG。BIXUYONGDAMIANJITONGBOSHI,ZUIHAOYONGZHAGEZHUANG,ZHEYANGYOULIYUPAICHUTONGBOYUJIBANJIANZHANHEJISHOURECHANSHENGDEHUIFAXINGQITI。

(4)HANPANZHONGXINKONGYAOBIQIJIANYINXIANZHIJINGSHAODAYIXIE。HANPANTAIDAYIXINGCHENGXUHAN。HANPANWAIJINGDYIBANBUXIAOYU(d+1.2)mm,QIZHONGdWEIYINXIANKONGJING。DUIGAOMIDUDESHUZIDIANLU,HANPANZUIXIAOZHIJINGKEQU(d+1.0) mm。

 3.2 PCBJIDIANLUKANGGANRAOCUOSHI

AG体育  YINSHUADIANLUBANDEKANGGANRAOSHEJIYUJUTIDIANLUYOUZHUMIQIEDEGUANXI,ZHELIJINJIUPCBKANGGANRAOSHEJIDEJIXIANGCHANGYONGCUOSHIZUOYIXIESHUOMING。

AG体育  (1)DIANYUANXIANSHEJI

AG体育 GENJUYINSHUAXIANLUBANDIANLIUDEDAXIAO,JINLIANGJIACUDIANYUANXIANKUANDU,JIANSHAOHUANLUDIANZU;TONGSHI,SHIDIANYUANXIAN、DIXIANDEZOUXIANGHESHUJUCHUANDIDEFANGXIANGYIZHI,ZHEYANGYOUZHUYUZENGQIANGKANGZAOSHENGNENGLI。

AG体育  (2)DIXIANSHEJI

 在單片機系統設計中,接地是控制干擾的重要方法。如能將接地和屏蔽正確結合起來使用,可解決大部分干擾問題。單片機AG体育系統中地線結構大致有系統地、機殼地(屏蔽地)、數字地(邏輯地)和模擬地等。在地線設計中應注意以下幾點:

① ZHENGQUEXUANZEDANDIANJIEDIYUDUODIANJIEDI。ZAIDIPINDIANLUZHONG,XINHAODEGONGZUOPINLVXIAOYU1 MHz,TADEBUXIANHEQIJIANJIANDEDIANGANYINGXIANGJIAOXIAO,ERJIEDIDIANLUXINGCHENGDEHUANLIUDUIGANRAOYINGXIANGJIAODA,YINERYINGCAIYONGYIDIANJIEDIDEFANGSHI。DANGXINHAOGONGZUOPINLVDAYU10 MHzSHI,DIXIANZUKANGBIANDEHENDA,CISHIYINGJINLIANGJIANGDIDIXIANZUKANG,YINGCAIYONGJIUJINDUODIANJIEDI。DANGGONGZUOPINLVZAI1~10MHzSHI,RUGUOCAIYONGYIDIANJIEDI,QIDIXIANCHANGDUBUYINGCHAOGUOBOCHANGDE1/20,FOUZEYINGCAIYONGDUODIANJIEDIFA。

AG体育 ② SHUZIDIYUMONIDIFENKAI。DIANLUBANSHANGJIYOUGAOSULUOJIDIANLU,YOUYOUXIANXINGDIANLU,YINGSHITAMENJINLIANGFENKAI,ERLIANGZHEDEDIXIANBUYAOXIANGHUN,FENBIEYUDIANYUANDUANDIXIANXIANGLIAN。DIPINDIANLUDEDIYINGJINLIANGCAIYONGDANDIANBINGLIANJIEDI,SHIJIBUXIANYOUKUNNANSHIKEBUFENCHUANLIANHOUZAIBINGLIANJIEDI;GAOPINDIANLUYICAIYONGDUODIANCHUANLIANJIEDI,DIXIANYINGDUANERCU。GAOPINYUANJIANZHOUWEIJINLIANGYONGZHAGEZHUANGDAMIANJIDIBO,YAOJINLIANGJIADAXIANXINGDIANLUDEJIEDIMIANJI。

③ JIEDIXIANYINGJINLIANGJIACU。RUOJIEDIXIANYONGHENXIDEXIANTIAO,ZEJIEDIDIANWEIHUISUIDIANLIUDEBIANHUAERBIANHUA,ZHISHIDIANZICHANPINDEDINGSHIXINHAODIANPINGBUWEN,KANGZAOSHENGXINGNENGJIANGDI。YINCIYINGJIANGJIEDIXIANJINLIANGJIACU,SHITANENGTONGGUOSANBEIYUYINSHUADIANLUBANDEYUNXUDIANLIU。RUYOUKENENG,JIEDIXIANDEKUANDUYINGDAYU3 mm。

④ JIEDIXIANGOUCHENGBIHUANLU。SHEJIZHIYOUSHUZIDIANLUZUCHENGDEYINSHUADIANLUBANDEDIXIANXITONGSHI,JIANGJIEDIXIANZUOCHENGBILUKEYIMINGXIANDITIGAOKANGZAOSHENGNENGLI。QIYUANYINZAIYU:YINSHUADIANLUBANSHANGYOUHENDUOJICHENGDIANLUYUANJIAN,YOUQIYUYOUHAODIANDUODEYUANJIANSHI,YINSHOUJIEDIXIANCUXIDEXIANZHI,HUIZAIDIXIANSHANGCHANSHENGJIAODADEDIANWEICHA,YINQIKANGZAONENGLIXIAJIANG;RUOJIANGJIEDIXIANGOUCHENGHUANLU,ZEHUISUOXIAODIANWEICHAZHI,TIGAODIANZISHEBEIDEKANGZAOSHENGNENGLI。

AG体育 (3)TUIOUDIANRONGPEIZHI

AG体育 PCBSHEJIDECHANGGUIZUOFAZHIYI,SHIZAIYINSHUABANDEGEGEGUANJIANBUWEIPEIZHISHIDANGDETUIOUDIANRONG。TUIOUDIANRONGDEYIBANPEIZHIYUANZESHI:

AG体育 ① DIANYUANSHURUDUANKUAJIE10~100μFDEDIANJIEDIANRONGQI。RUYOUKENENG,JIE100μFYISHANGDEGENGHAO。

② YUANZESHANGMEIGEJICHENGDIANLUXINPIANDOUYINGBUZHIYIGE0.01 pFDECIPIANDIANRONG。RUYUYINSHUABANKONGXIBUGOU,KEMEI4~8GEXINPIANBUZHIYIGE1~10 pFDETANDIANRONG。

AG体育 ③ DUIYUKANGZAONENGLIRUO、GUANDUANSHIDIANYUANBIANHUADADEQIJIAN,RURAM、ROMCUNCHUQIJIAN,YINGZAIXINPIANDEDIANYUANXIANHEDIXIANZHIJIANZHIJIEJIERUTUIOUDIANRONG。

④ DIANRONGYINXIANBUNENGTAICHANG,YOUQISHIGAOPINPANGLUDIANRONGBUNENGYOUYINXIAN。

AG体育 CIWAI,HUANYINGZHUYIYIXIALIANGDIAN:

① ZAIYINSHUABANZHONGYOUJIECHUQI、JIDIANQI、ANNIUDENGYUANJIANSHI,CAOZUOTAMENSHIJUNHUICHANSHENGJIAODAHUOHUAFANGDIAN,BIXUCAIYONGRCDIANLULAIXISHOUFANGDIANDIANLIU。YIBANRQU1~2 kΩ,CQU2.2~47μF。

②CMOSDESHURUZUKANGHENGAO,QIEYISHOUGANYING,YINCIZAISHIYONGSHI,DUIBUYONGDUANYAOJIEDIHUOJIEZHENGDIANYUAN。

(4)ZHENDANGQI

  幾乎所有的單片機都有一個耦合于外部晶體或陶瓷諧振器的振蕩器電路。在PCB上,要求外接電容、晶體或陶瓷諧振器的引線越短越好。RC振蕩器對干擾信號有潛在的敏感性,它能產生很短的時鐘周期,因而最好選晶體或陶瓷諧振器。另外,石英晶體的外殼要接地。

(5)FANGLEIJICUOSHI

  室外使用的單片機系統或從室外架空引入室內的電源線、信號線,要考慮系統的防雷擊問題。常用的防雷擊器件有:氣體放電管、TVS(Transient Voltage Suppression)等。氣體放電管是當電源電壓大于某一數值時,通常為數十V或數百V,氣體擊穿放電,將電源線上強沖擊脈沖導入大地。TVS可以看成兩個并聯且方向相反的齊納二極管,當兩端電壓高于某一值時導通。其特點是可以瞬態通過數百乃至上千A的電流。

AG体育  JIESHUYU

     為了提高單片機系統的電磁兼容性,不僅要合理設計PCB板,而且要在電路結構上及軟件中采取相應的措施。實踐表明,在單片機系統的設計、制造、安裝和運行的各個階段,都需要考慮其電磁兼容性,只有這樣,才能保證系統長期穩定、可靠、安全地運行。

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