Yuav ua li cas kom tsis txhob kis kab mob hauv kev kub ceev PCB tsim?

Yuav ua li cas kom tsis txhob kis kab mob cuam tshuam hauv kev kub ceev PCB tsim

1. Txoj hauv kev los tiv thaiv hluav taws xob cuam tshuam

Kev daws teeb meem zoo rau teeb meem kev ncaj ncees yuav txhim kho kev sib nqus sib nqus (EMC) ntawm PCB pawg thawj coj. Ib qho tseem ceeb tshaj plaws yog kom ntseeg tau tias PCB lub rooj tsavxwm muaj cov hauv paus zoo. Lub teeb liab txheej nrog txheej txheej hauv av yog txoj hauv kev zoo heev rau kev tsim qauv. Ib qho ntxiv, txo qis qhov teeb meem ntom ntom ntawm txheej txheej sab nrauv ntawm lub rooj tsav xwm hauv Circuit Court kuj tseem yog txoj hauv kev zoo los txo hluav taws xob hluav taws xob. Txoj hauv kev no tuaj yeem ua tiav los ntawm kev siv “thaj chaw” thev naus laus zis “tsim” PCB tsim. Cov txheej txheem txheej saum npoo av tau ua tiav los ntawm kev ntxiv kev sib xyaw ua ke ntawm txheej txheej txheej nyias nyias thiab micropores siv los nkag rau cov txheej txheem no ntawm txheej txheem txheej txheem PCB. Kev tiv thaiv thiab lub peev xwm tuaj yeem faus hauv qab saum npoo, thiab qhov ntom ntom ntom ntom ntom ntom ntom ntab ib cheeb tsam ze li ob npaug, yog li txo qhov ntim ntawm PCB. Kev txo qis ntawm thaj tsam PCB muaj kev cuam tshuam loj heev rau cov txheej txheem txheej txheem, uas txhais tau tias lub voj tam sim no tau raug txo, qhov ntev ntawm cov ceg kev hloov pauv tau raug txo, thiab cov hluav taws xob hluav taws xob tau kwv yees li ib feem ntawm thaj tsam ntawm lub voj tam sim no; At the same time, the small size characteristics mean that high-density pin packages can be used, which in turn reduces the length of the wire, thus reducing the current loop and improving emc characteristics.

2. Strictly control the cable lengths of key network cables

If the design has a high speed jump edge, the transmission line effect on the PCB must be considered. Lub moos siab tus nqi nrawm suav nrog cov khoom siv hluav taws xob uas niaj hnub siv niaj hnub no tseem muaj teeb meem ntau dua. Muaj qee cov hauv paus ntsiab lus los daws qhov teeb meem no: yog tias siv CMOS lossis TTL kev tsim hluav taws xob, kev ua haujlwm tsawg dua 10MHz, thiab qhov ntev txuas yuav tsum tsis pub ntau dua 7 ntiv. If the operating frequency is 50MHz, the cable length should not be greater than 1.5 inches. Wiring length should be 1 inch if operating frequency reaches or exceeds 75MHz. Qhov ntev tshaj plaws thaiv kab rau GaAs chips yuav tsum yog 0.3 ntiv tes. Yog tias qhov no dhau, muaj teeb meem kab sib kis.

3. Ua kom tau raws li txheej txheem txheej txheem txheej txheem txheej txheem

Lwm txoj hauv kev los daws qhov kab mob kis tau zoo yog xaiv txoj hauv kev kom raug thiab lub davhlau ya nyob twg. Cov kab hluav taws xob sab saum toj hais txog cov kab sib txuas ua ke thiab cov qauv ntawm cov xov tooj sib txuas. Thaum siv cov cuab yeej siv logic nrawm, lub teeb liab nrog cov hloov pauv sai yuav cuam tshuam los ntawm cov ceg ntoo ntawm lub teeb liab tshwj tsis yog cov ceg ntev khaws cia luv heev. Feem ntau, PCB txoj hauv kev tau txais ob txoj hauv kev yooj yim, uas yog Daisy Chain routing thiab Star tis.

Rau daisy-saw thaiv, thaiv pib ntawm tus neeg tsav tsheb kawg thiab mus txog txhua qhov tau txais qhov kawg tig. Yog tias cov tshuaj tiv thaiv kab mob tau siv los hloov cov yam ntxwv ntawm lub teeb liab, txoj haujlwm ntawm cov khoom tiv thaiv yuav tsum nyob ze rau qhov kawg ntawm kev tsav tsheb. Daisy saw cabling yog qhov zoo tshaj plaws hauv kev tswj hwm kev sib raug zoo ntawm kev sib txuas. Txawm li cas los xij, hom xov hlau no muaj tus nqi qis tshaj thiab tsis yooj yim kom dhau 100%. Hauv qhov tsim qauv tiag tiag, peb xav ua kom cov ceg ntoo ntev hauv Daisy saw hlau txuas kom luv li sai tau, thiab kev nyab xeeb ntev tus nqi yuav tsum yog: Stub qeeb < = Txt * 0.1.

Piv txwv li, cov ceg xaus hauv kev siv hluav taws xob TTL nrawm yuav tsum tsawg dua 1.5 ntiv ntev. Cov txheej txheem sab saum toj no siv qhov chaw txuas tsawg dua thiab tuaj yeem raug txiav tawm los ntawm kev sib txuas ib leeg. Txawm li cas los xij, cov qauv thaiv no ua rau lub teeb liab tau txais ntawm cov teeb liab sib txawv tau txais tsis sib xws.

The star topology can effectively avoid the problem of clock signal synchronization, but it is very difficult to finish the wiring manually on the PCB with high density. Siv cov cab cab tsis siv neeg yog txoj hauv kev zoo tshaj plaws kom ua tiav lub hnub qub cabling. A terminal resistor is required on each branch. The value of the terminal resistance should match the characteristic impedance of the wire. Qhov no tuaj yeem ua tiav ntawm tus kheej lossis dhau los ntawm CAD cov cuab yeej los xam cov yam ntxwv tsis muaj txiaj ntsig zoo thiab lub davhlau ya nyob twg sib piv qhov tseem ceeb.

While simple terminal resistors are used in the two examples above, a more complex matching terminal is optional in practice. Thawj qhov kev xaiv yog lub davhlau ya nyob twg RC. RC sib txuas cov dav hlau tuaj yeem txo kev siv hluav taws xob, tab sis tsuas yog siv tau thaum lub teeb liab ua haujlwm tau ruaj khov. Txoj kev no yog qhov tsim nyog tshaj plaws rau moos kab teeb liab sib txuam ua. Qhov tsis zoo yog tias lub peev xwm hauv RC sib piv lub davhlau ya nyob twg tuaj yeem cuam tshuam rau qhov zoo thiab nthuav tawm qhov nrawm ntawm lub teeb liab.

The series resistor matching terminal incurs no additional power consumption, but slows down signal transmission. This approach is used in bus-driven circuits where time delays are not significant. Cov kab hluav taws xob sib txuas ua ke lub davhlau ya nyob twg kuj muaj qhov zoo ntawm kev txo tus naj npawb ntawm cov cuab yeej siv ntawm lub rooj tsavxwm thiab qhov ntom ntawm kev sib txuas.

The final method is to separate the matching terminal, in which the matching element needs to be placed near the receiving end. Nws qhov zoo yog tias nws yuav tsis rub lub teeb liab, thiab tuaj yeem ua tau zoo kom tsis txhob muaj suab nrov. Feem ntau siv rau TTL cov cim qhia (ACT, HCT, FAST).

In addition, the package type and installation type of the terminal matching resistor must be considered. SMD surface mount resistors generally have lower inductance than through-hole components, so SMD package components are preferred. There are also two installation modes for ordinary straight plug resistors: vertical and horizontal.

Hauv kev teeb tsa ntsug, kev tiv thaiv muaj tus pin mounting luv, uas txo cov cua sov ua haujlwm nruab nrab ntawm qhov tsis kam thiab lub rooj tsav xwm hauv Circuit Court thiab ua rau cov cua sov ua kom yooj yim dua rau hauv huab cua. Tab sis kev teeb tsa ntsug ntev dua yuav ua rau qhov inductance ntawm resistor. Kev teeb tsa kab rov tav muaj qhov qis qis vim yog kev teeb tsa qis dua. However, the overheated resistance will drift, and in the worst case, the resistance will become open, resulting in PCB wiring termination matching failure, becoming a potential failure factor.

4. Lwm yam thev naus laus zis

Txhawm rau txo qis kev siv hluav taws xob ntau dhau ntawm IC lub zog hluav taws xob, txiav tawm lub tshuab hluav taws xob yuav tsum tau ntxiv rau IC nti. Qhov no tshem tawm qhov cuam tshuam ntawm burrs ntawm lub zog hluav taws xob thiab txo qis hluav taws xob los ntawm lub voj voos hluav taws xob ntawm daim ntawv luam tawm.

Cov nyhuv ua kom zoo dua qub yog qhov zoo tshaj plaws thaum lub peev txheej txiav tawm tau txuas ncaj qha rau lub zog hluav taws xob ceg ntawm kev sib koom ua ke ntau dua li rau txheej txheej fais fab. Qhov no yog vim li cas qee cov khoom siv tau txiav cov capacitors hauv lawv lub qhov, thaum lwm tus xav tau qhov kev ncua deb ntawm lub tshuab txiav tawm thiab lub cuab yeej kom me me txaus.

Txhua qhov nrawm thiab siv lub zog siv hluav taws xob siab yuav tsum tau muab tso ua ke kom deb li deb tau kom txo qis kev siv hluav taws xob ntau dhau.

Tsis muaj txheej txheej hluav taws xob, cov kab hluav taws xob ntev tsim lub voj nruab nrab ntawm lub teeb liab thiab lub voj, ua lub hauv paus ntawm hluav taws xob thiab hluav taws xob inductive.

Kev sib dhos ua lub voj uas tsis dhau los ntawm tib lub network cable lossis lwm yam cabling hu ua open loop. Yog tias lub voj hla los ntawm tib lub network cable, lwm txoj hauv kev tsim lub voj kaw. Hauv ob qho tib si, cov kav hlau txais xov (kab kav hlau txais xov thiab lub kav hlau txais xov ntiv nplhaib) tuaj yeem tshwm sim.