PCB layout great influence on the PCB electromagnetic compatibility, the circuit in order to work on the PCB, and the wiring should be optimized components / connectors and IC according to certain constraints described herein spent coupling circuit layout
(A), choice of the PCB material
Through the wiring line path and the printed material PCB reasonable choice may be made of other low line coupled transmission lines. When the distance d between the transmission line conductors is smaller than the distance between other adjacent conductors of the same, can achieve a lower coupling, crosstalk or less (see "Electronic Engineering Times," 2000 1 "Application Guide").
Prior to design, to select the most economical form of a PCB according to the following conditions:
EMC requirements of
PCB denseness
The ability to assemble and production
CAD system capabilities
Design costs
Number of PCB
Electromagnetic shielding costs
When a non-shielded enclosure product structure, with particular attention to the overall cost of the product / component package / pin style, PCB form, electromagnetic shielding, construction and assembly), in many cases, selecting the right may not necessarily be in the form of a PCB was added plastic shell metal shield box.
In order to improve the noise immunity and high-speed analog digital applications while reducing all harmful radiation, the need to use the transmission line technology. The conversion of the output signal, the transmission line between the S-VCC, S-VEE and VEE-VCC needs represented as shown in FIG.
Signal current is determined by the symmetry of the output stage circuit. On the MOS For IOL = IOH, while the TTL For IOL> IOH.
Function / logical type ZO (Ω)
Power (typical) <10 ecl="" logic="" 50="" ttl="" logic="" 100="" hc="" (t)="" logic="" 200="" table="" 1:="" some="" transmission="" line="" impedance="" of="" the="" signal="" path="" zo.="" logic="" and="" functional="" reasons="" type="" determines="" the="" typical="" characteristic="" impedance="" of="" the="" transmission="" line="" zo,="" as="" shown="" in="" table="" 1.="" figure="" 1:="" shows="" a="" typical="" interconnection="" diagram="" between="" three="" specific="" transmission="" line="" (number)="" the="" ic="" fig="" 2:="" ic="" decoupling="" circuit.="" figure="" 3:="" correct="" decoupling="" circuit="" block="" table="" 2:="" decoupling="" the="" recommended="" value="" of="" the="" capacitance="" of="" cdec="" ...="" logic="" circuit="" noise="" margin="" (b),="" the="" signal="" circuit="" and="" the="" signal="" line="" to="" its="" loop="" signal="" line="" transmitting="" a="" signal="" as="" close="" as="" possible,="" to="" prevent="" the="" loop="" area="" enclosed="" by="" these="" lines="" to="" generate="" radiation,="" and="" reduces="" the="" susceptibility="" induced="" voltage="" loop.="" generally,="" when="" the="" distance="" between="" the="" two="" lines="" of="" equal="" width,="" the="" coupling="" coefficient="" of="" about="" 0.5="" to="" 0.6,="" and="" the="" effective="" inductance="" of="" the="" line="" from="" 1μh="" m="" down="" 0.4-0.5μ="" h="" m.="" this="" means="" that="" 40%="" to="" 50%="" free="" signal="" circuit="" current="" flows="" to="" the="" other="" lines="" on="" the="" pcb.="" a="" signal="" path="" between="" each="" two="" (sub)="" block="" circuit,="" whether="" analog="" or="" digital,="" can="" be="" represented="" by="" three="" transmission="" lines,="" shown="" in="" figure="" 1,="" wherein="" the="" impedance="" can="" be="" obtained="" from="" table="" 1.="" when="" converted="" from="" ttl="" logic="" high="" level="" to="" a="" low="" level,="" the="" absorption="" will="" be="" greater="" than="" the="" current="" supply="" current="" to,="" in="" this="" case,="" the="" transmission="" line="" is="" generally="" defined="" between="" vcc="" and="" s,="" but="" not="" between="" s="" and="" vee.="" by="" using="" the="" ferrite="" bead="" and="" the="" signal="" line="" loop="" current="" signal="" lines="" can="" be="" completely="" controlled.="" in="" the="" case="" of="" parallel="" conductors,="" the="" characteristic="" impedance="" of="" the="" transmission="" line="" will="" be="" affected="" because="" of="" the="" ferrite,="" in="" the="" case="" of="" the="" coaxial="" cable,="" the="" cable="" ferrite="" external="" parameters="" will="" only="" influence.="" thus,="" adjacent="" lines="" should="" be="" as="" thin="" as="" possible,="" the="" opposite="" vertically="" arranged="" (usually="" a="" distance="" less="" than="" the="" thickness="" of="" 1.5mm="" epoxy="" bilayer="" plate).="" it="" should="" be="" routed="" so="" that="" each="" signal="" line="" and="" as="" close="" as="" possible="" to="" its="" signal="" circuit="" (signal="" and="" power="" supply="" wiring="" are="" applicable).="" if="" not="" enough="" coupling="" between="" the="" transmission="" line="" conductor,="" a="" ferrite="" bead="" may="" be="" used.="" (c),="" ic="" decoupling="" ic="" typically="" achieve="" only="" by="" decoupling="" capacitance="" because="" capacitance="" is="" not="" ideal,="" it="" will="" resonate.="" when="" the="" resonance="" frequency="" is="" greater="" than="" the="" capacitance="" behave="" like="" an="" inductance,="" which="" means="" that="" di="" dt="" is="" limited.="" the="" value="" of="" the="" capacitance="" between="" the="" ic="" pins="" allowed="" by="" the="" power="" supply="" voltage="" fluctuation="" is="" determined,="" according="" to="" practical="" experience="" experienced="" designer,="" voltage="" fluctuations="" should="" be="" less="" than="" 25%="" of="" the="" noise="" margin="" under="" the="" worst-case="" signal="" line,="" the="" following="" equation="" can="" be="" calculated="" for="" each="" logic="" best="" decoupling="" capacitance="" value="" of="" the="" output="" of="" the="" gate="" circuit="" the="" series:="" i="c" dv="" dt?="" table="" 2="" shows="" several="" series="" of="" logic="" gates="" the="" signal="" line="" noise="" margin="" in="" the="" worst="" case,="" each="" output="" stage="" is="" also="" given="" decoupling="" capacitors="" should="" be="" added="" cdec.="" recommended="" values.="" figure="" 4:="" pcb="" radiation="" on="" the="" loop="" fast="" logic="" circuit,="" if="" a="" large="" decoupling="" capacitor="" comprises="" a="" series="" inductance="" (that="" may="" be="" caused="" by="" the="" inductance="" of="" the="" printed="" circuit="" structure="" of="" the="" capacitor,="" the="" length="" of="" the="" cable="" or="" pcb),="" the="" capacitance="" value="" may="" no="" longer="" be="" useful.="" additional="" time="" is="" necessary="" to="" add="" a="" small="" ceramic="" capacitor="" (100-100pf),="" and="" "lf-"="" as="" close="" to="" ic="" pins="" decoupling="" capacitors="" in="" parallel.="" ceramic="" capacitors="" of="" the="" resonance="" frequency="" (the="" length="" of="" the="" line="" including="" the="" power="" supply="" ic="" pins)="" should="" be="" higher="" than="" the="" bandwidth="" of="" the="" logic="" circuits="" [1="" (π.τr)],="" where,="" τr="" is="" the="" rise="" time="" of="" the="" voltage="" of="" the="" logic="" circuit.="" if="" each="" ic="" has="" decoupling="" capacitors,="" a="" current="" loop="" signal="" path="" select="" the="" most="" convenient,="" the="" vcc="" or="" vee,="" which="" may="" be="" determined="" by="" the="" mutual="" coupling="" between="" the="" transmission="" line="" and="" power="" line="" signals.="" ltrace="" inductance="" between="" two="" decoupling="" capacitors="" (one="" for="" each="" ic)="" and="" power="" supply="" lines="" are="" formed,="" it="" will="" form="" a="" series="" resonant="" circuit,="" such="" a="" resonator="" can="" only="" occur="" at="" low="" frequencies="">
<= 2="" of="" the="" case.="" by="" high="" rf="" losses="" choke="" coil="" connected="" in="" series="" and="" the="" network="" to="" be="" decoupled="" vcc="" ic,="" the="" resonance="" frequency="" can="" kept="" below="" 1mhz,="" if="" too="" low="" rf="" loss="" can="" be="" compensated="" by="" a="" parallel="" or="" series="" resistance="" (fig.="" 2).="" the="" choke="" coil="" should="" always="" be="" closed="" core="" employed,="" otherwise="" it="" will="" be="" a="" radio="" frequency="" transmitter="" iron="" or="" magnetic="" field="" sensors.="" for="" example:="" 1mhz="" *="" 1μhz="" z1="6.28Ω" rs="3.14Ω" q<2="" rp="12.56Ω" is="" greater="" than="" the="" resonant="" frequency,="" characterized="" "transmission="" line"="" impedance="" z0="" of="" (at="" this="" time="" is="" regarded="" as="" the="" power="" supply="" ic="" impedance="" load)="" is="" equal="" to:="" z0="(Ltrace" cdecoupling)="" the="" square="" root="" decoupling="" capacitor="" and="" the="" inductance="" of="" the="" series="" inductance="" of="" the="" connecting="" line="" rf="" power="" has="" little="" effect="" on="" the="" current="" distribution,="" such="" as="" the="" case="" of="" using="" a="" choke="" coil="" 1μh.="" but="" it="" still="" determines="" the="" voltage="" fluctuation="" between="" power="" pin="" ic,="" table="" 3="" gives="" the="" signal="" to="" noise="" power="" margin="" is="" 25%,="" the="" recommended="" maximum="" inductance="" ltrace.="" the="" decoupling="" method="" suggested="" by="" fig.="" 2,="" between="" the="" two="" ic="" reduce="" the="" number="" of="" transmission="" lines="" from="" 3="" to="" 1="" (see="" fig.="" 3).="" therefore,="" for="" each="" ic="" adequate="" decoupling="" method:="" lchoke="" +="" cdec="" defined="" only="" between="" circuit="" blocks="" on="" a="" transmission="" line.="" for="" τr<3ns="" speed="" logic="" circuit,="" and="" all="" the="" series="" inductance="" decoupling="" capacitor="" must="" be="" low="" (see="" table="" 3).="" decision="" series="" with="" a="" power="" pin="" of="" the="" printed="" circuit="" is="" equivalent="" to="" a="" 50mm="" 50hh="" inductor,="" and="" an="" output="" terminal="" of="" the="" load="" (typically="" 50pf)="" the="" minimum="" rise="" time="" of="" 3.2ns.="" such="" as="" requiring="" faster="" rise="" time,="" it="" is="" necessary="" to="" shorten="" the="" decoupling="" capacitors="" pins.="" length="" (preferably="" no="" pin)="" ic="" package="" pins="" and="" shortened,="" for="" example,="" an="" ic="" decoupling="" capacitors,="" or="" preferably="" using="" the="" (power="" supply)="" pin="" of="" the="" ic="" with="" a="" small="" intermediate="" distance="" 3e="" (the="" dil)="" leadless="" combining="" a="" ceramic="" capacitor="" and="" other="" methods="" to="" achieve="" this="" purpose,="" it="" can="" also="" be="" used="" with="" a="" power="" supply="" layer="" and="" a="" ground="" layer="" of="" the="" multilayer="" circuit="" board.="" another="" use="" power="" pins="" may="" be="" further="" improved="" in="" the="" middle="" so="" packages.="" however,="" when="" using="" fast="" logic="" circuits,="" a="" multilayer="" circuit="" board="" should="" be="" used.="" (iv),="" determined="" in="" accordance="" with="" the="" radiation="" loop="" area="" end="" of="" the="" transmission="" line="" without="" reflection="" determines="" the="" maximum="" length="" of="" the="" line.="" since="" the="" mandatory="" requirements="" for="" product="" em="" radiation,="" and="" thus="" the="" area="" of="" the="" loop="" line="" length="" area="" are="" limited,="" if="" the="" non-shielded="" enclosure,="" this="" restriction="" will="" be="" implemented="" directly="" by="" the="" pcb.="" note:="" if="" the="" load="" in="" the="" asynchronous="" series="" termination="" logic="" circuit="" design,="" it="" is="" necessary="" to="" pay="" attention="" to="" occur="" quasi-stability,="" especially="" symmetrically="" logic="" input="" circuit="" can="" not="" determine="" that="" the="" input="" signal="" is="" high="" or="" low,="" and="" may="" result="" in="" a="" non-defined="" output="" conditions.="" figure="" 3:="" correct="" decoupling="" circuit="" blocks.="" for="" logic="" signals="" in="" the="" frequency="" domain,="" the="" amplitude="" of="" the="" spectrum="" beyond="" the="" current="" logic="" signal="" bandwidth="" (="1" π.τr)="" the="" frequency="" is="" inversely="" proportional="" to="" the="" square="" of="" the="" frequency.="" it="" is="" represented="" by="" the="" angular="" frequency,="" the="" radiation="" impedance="" of="" the="" loop="" with="" frequency="" proportional="" to="" the="" square="" remains.="" thus="" calculated="" largest="" loop="" area,="" which="" consists="" of="" a="" repetition="" rate="" or="" clock="" rate,="" or="" bandwidth,="" and="" a="" current="" rise="" time="" the="" amplitude="" of="" the="" time="" domain="" signal="" of="" the="" decision="" logic.="" the="" current="" waveform="" determined="" by="" the="" voltage="" waveform="" and="" the="" current="" time="" is="" about="" equal="" to="" the="" half="" width="" of="" the="" voltage="" rise="" time.="" available="" current="" amplitude="" angular="" frequency="" (="1" π.τr)="" is="" expressed="" as:.="" i="" (f)="2.I" τr="" t="" where:="" i="the" magnitude="" of="" the="" current="" time="" domain;="" t="is" the="" reciprocal="" of="" the="" clock="" rate,="" i.e.="" the="" cycle;="" τr="" is="" the="" voltage="" rise="" time,="" the="" current="" is="" approximately="" equal="" to="" half="" the="" time="" width="" τh.="" calculated="" from="" this="" equation="" that="" a="" certain="" series="" of="" logic="" circuits="" at="" a="" maximum="" clock="" rate="" of="" the="" loop="" area,="" table="" 5="" shows="" the="" corresponding="" loop="" area.="" the="" largest="" loop="" area,="" the="" number="" of="" the="" logic="" type="" switch="" loop="" (="output" current)="" and="" the="" pcb="" is="" determined="" by="" the="" simultaneous="" presence="" of="" n="" clock="" rate.="" if="" the="" clock="" rate="" used="" is="" larger="" than="" 30mhz,="" it="" is="" necessary="" to="" employ="" a="" multilayer="" circuit="" board,="" in="" this="" case,="" the="" thickness="" of="" the="" epoxy="" resin="" layers="" related,="" between="" 60="" to="" 300μm.="" when="" only="" a="" limited="" number="" of="" high="" speed="" clock="" signal="" on="" the="" pcb,="" by="" using="" the="" wiring="" layers="" to="" the="" wiring="" layer="" carefully,="" may="" give="" acceptable="" results="" in="" the="" bilayer="" plate.="" note:="" in="" this="" case,="" as="" ordinary="" dil="" package,="" the="" loop="" area="" will="" exceed="" limits,="" there="" must="" be="" additional="" shielding="" measures="" and="" appropriate="" filtering.="" all="" panels="" and="" connected="" to="" the="" other="" connector="" components="" must="" be="" placed="" close="" to="" each="" other="" as="" possible,="" so="" that="" the="" cable="" conducting="" the="" common="" mode="" current="" can="" not="" flow="" in="" the="" pcb="" circuit="" lines,="" further,="" the="" voltage="" drop="" between="" the="" reference="" points="" on="" the="" pcb="" can="" not="" be="" excited="" (="" antenna)="" cable.="" to="" avoid="" such="" influence="" of="" common="" mode,="" the="" reference="" must="" be="" close="" to="" the="" connectors="" and="" the="" ground="" layer="" of="" the="" circuit,="" a="" ground="" circuit="" spaced="" grid="" or="" reference="" to="" the="" pcb,="" if="" possible="" these="" should="" be="" ground="" to="" the="" metal="" casing="" sheet="" product.="" from="" this="" ground="" plate,="" only="" the="" high-resistance="" devices="" such="" as="" inductors,="" resistors,="" reed="" relay="" and="" the="" optical="" coupler="" can="" be="" connected="" between="" the="" two="" places.="" all="" connections="" are="" placed="" as="" close="" as="" possible,="" to="" prevent="" external="" reference="" current="" flows="" through="" the="" line="" or="" on="" the="" pcb.="" (e),="" selecting="" the="" correct="" cables="" and="" connectors="" selection="" of="" the="" cable="" is="" determined="" by="" the="" amplitude="" and="" frequency="" of="" the="" signal="" flowing="" through="" the="" cable="" components.="" for="" products="" located="" outside="" the="" cable,="" if="" the="" data="" signal="" transfer="" clock="" rate="" than="" 10khz,="" it="" must="" use="" the="" shield="" (product="" requirements),="" the="" shield="" portion="" to="" be="" connected="" to="" ground="" (metal="" products)="" in="" the="" ends="" of="" the="" cable,="" this="" will="" ensure="" of="" electric="" and="" magnetic="" fields="" are="" shielded.="" if="" using="" a="" separate="" ground,="" it="" should="" be="" connected="" to="" the="" "ground="" connection"="" rather="" than="" "circuit="" ground."="" if="" the="" clock="" rate="" is="" between="" 10khz="" to="" 1mhz,="" and="" the="" rise="" time="" of="" the="" logic="" circuit="" is="" kept="" low="" as="" possible,="" it="" will="" be="" 80%="" or="" more="" of="" light="" covering="" less="" than="" or="" transfer="" impedance="" 10nh="" m="" in.="" if="" the="" clock="" rate="" than="" 1mhz,="" requires="" a="" better="" shielded="" cable.="" typically,="" in="" addition="" to="" a="" coaxial="" cable,="" shielded="" cable="" is="" not="" applied="" as="" a="" signal="" circuit.="" by="" passive="" filters="" in="" series="" between="" the="" signal="" input="" output="" and="" ground="" reference="" point="" in="" order="" to="" reduce="" radio="" frequency="" components,="" shielding="" may="" not="" necessarily="" with="" high="" quality="" and="" the="" corresponding="" terminal.="" good="" shielded="" cable="" should="" be="" provided="" with="" a="" suitable="" connector.="">
Our other product:
