A Practical Guide to High Speed Printed Circuit Board Layout

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DESIGNATE WHICH COMPONENTS NEED TO BE ON TOP OF THE BOARD
INCLUDE TUNING INFORMATION COMPONENT VALUE RANGES THERMAL
INFORMATION CONTROLLED IMPEDANCE LINES NOTES BRIEF CIRCUIT
OPERATINGDESCRIPTIONSxANDTHELISTGOESON

4RUST.O/NE

)F YOURE NOT DOING YOUR OWN LAYOUT BE SURE TO SET ASIDE AMPLE
TIMETOGOTHROUGHTHEDESIGNWITHTHELAYOUTPERSON!NOUNCEOF
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MINIMIZEREWORKINGTHEBOARDLAYOUT

9OURINSTRUCTIONSFORTHEDESIGNERSHOULDINCLUDEABRIEFDESCRIPTION
OFTHECIRCUITSFUNCTIONSASKETCHOFTHEBOARDTHATSHOWSTHEINPUT
ANDOUTPUTLOCATIONSTHEBOARDSTACKUPIEHOWTHICKTHEBOARD
WILLBEHOWMANYLAYERSDETAILSOFSIGNALLAYERSANDPLANESˆPOWER

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LINESNEEDTOBECONTROLLEDIMPEDANCELINESWHICHLINESNEEDTO
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AWAYFROMORNEAREACHOTHERWHICHCIRCUITSNEEDTOBEKEPTAWAY
FROMORNEAREACHOTHERWHICHCOMPONENTSNEEDTOBECLOSETOOR
AWAYFROMEACHOTHERWHICHCOMPONENTSGOONTHETOPANDTHE
BOTTOMOFTHEBOARD9OULLNEVERGETACOMPLAINTFORGIVINGSOMEONE
TOOMUCHINFORMATIONˆTOOLITTLEYESTOOMUCHNO

! LEARNING EXPERIENCE !BOUT YEARS AGO ) DESIGNED A
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FORHIGHSPEEDOPAMPSANDANYOTHERHIGHSPEEDCIRCUITRY4HERE
ARETWOCOMMONLYUSEDCONlGURATIONSFORBYPASSINGHIGHSPEED
OPAMPS

2AILSTOGROUND4HISTECHNIQUEWHICHWORKSBESTINMOSTCASES
USES MULTIPLE PARALLEL CAPACITORS CONNECTED FROM THE OP AMPS
POWERSUPPLY PINS DIRECTLY TO GROUND 4YPICALLY TWO PARALLEL
CAPACITORS ARE SUFlCIENTˆBUT SOME CIRCUITS MAY BENElT FROM
ADDITIONALCAPACITORSINPARALLEL

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ALOWIMPEDANCEPATHTOGROUNDFORMANYDECADESOFFREQUENCY
WILLHELPENSURETHATUNWANTEDNOISEDOESNTlNDITSWAYINTOTHE
OPAMP&IGURESHOWSTHEBENElTSOFMULTIPLEPARALLELCAPACITORS
!TLOWERFREQUENCIESTHELARGERCAPACITORSOFFERALOWIMPEDANCE
PATHTOGROUND/NCETHOSECAPACITORSREACHSELFRESONANCETHE
CAPACITIVEQUALITYDIMINISHESANDTHECAPACITORSBECOMEINDUCTIVE
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CAPACITORSFREQUENCYRESPONSEISROLLINGOFFANOTHERISBECOMING
SIGNIlCANTTHEREBYMAINTAININGALOWACIMPEDANCEOVERMANY
DECADESOFFREQUENCY

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