ADI的高速PCB设计

The World Leader in High Performance Signal Processing SolutionsA Practical Guide toHigh-Speed Printed CircuitBoard LayoutAgendaOverviewSchematicLocation location locationLocation, location, locationPower supply bypassingParasiticsGround and power planesPackagingRF Signal routing and shielding SummaryOverviewPCB layout is one of the last steps in the design process and often one of the most criticalHigh-speed circuit performance is heavily dependant onHigh speed circuit performance is heavily dependant on layoutA high-performance design can be rendered useless due to a poor or sloppy layoutpoor or sloppy layoutToday’s presentation will help:p y pz Improve the layout processz Ensure expected circuit performance is achievedz Reduce design timeL tz Lower costz Lower stress for you and the PCB designerThe World Leader in High Performance Signal Processing SolutionsSchematicSchematicA good layout starts with a good Schematic! Schematic flow and contentInclude as much information as you canInclude as much information as you canWhat should you include?Items to Include on a Schematic N tNotesComponent tolerances and case sizesPart numbers (internal/external/alternative)Board stack upTests or alignment procedurespPower dissipationControlled impedance and line matchingComponent de-ratingThermal requirementsThermal requirementsKeep outsMechanical considerationsCritical component placementCritical component placementWarning flagsWhat ever else you can think of!SchematicThe World Leader in High Performance Signal Processing SolutionsLocation, location, location! Location location location!Location, Location, LocationLocation Location LocationJust as in real estate location is everything!Input/output and power connections are typically defined…Everything else is undefinedd fi d E thi l i d fi dz Critical component placementSignal routingz Signal routingz Circuit and component proximityThe World Leader in High Performance Signal Processing SolutionsPower Supply BypassingPower Supply BypassingBypassing is essential tohigh speed circuitpperformanceCapacitors right at powersupply pinsCapacitors provide low ACz Capacitors provide low ACimpedance to groundz Provide local charge storagefor fast rising/falling edgesf f t i i/f lli dPower Supply BypassingBypassing is essential tohigh speed circuitperformance +V S L1pCapacitors right at powersupply pinsCapacitors provide low ACIC C10.1µF 1µH z Capacitors provide low AC impedance to groundz Provide local charge storagef f t i i /f lli dµfor fast rising/falling edges Keep trace lengths shortEQUIVALENT DECOUPLED POWER LINE CIRCUIT RESONATES AT:f =1f =2πLC √f = 500kHzPower Supply BypassingBypassing is essential tohigh speed circuitpperformanceCapacitors right at powersupply pinsCapacitors provide low ACz Capacitors provide low ACimpedance to groundz Provide local charge storagefor fast rising/falling edgesf f t i i/f lli dKeep trace lengths shortPower Supply BypassingBypassing is essential tohigh speed circuitpperformanceCapacitors right at powersupply pinsCapacitors provide low ACz Capacitors provide low ACimpedance to groundz Provide local charge storagefor fast rising/falling edgesf f t i i/f lli dKeep trace lengths shortClose to load returnClose to load returnz Helps minimize transientcurrents in the ground planePower Supply BypassingB i i ti l tBypassing is essential to high speed circuit performanceC i i hCapacitors right at power supply pins z Capacitors provide low AC i d t dimpedance to groundz Provide local charge storage for fast rising/falling edgesK t l th h tKeep trace lengths short Close to load returnz Helps minimize transient pcurrents in the ground planeValuesz Individual circuit performance d dua c cu t pe o a cePower Supply Bypassing B i i ti l tBypassing is essential tohigh speed circuitperformanceC i i hCapacitors right at powersupply pinsz Capacitors provide low ACimpedance to groundimpedance to groundz Provide local charge storage forfast rising/falling edgesKeep trace lengths shortKeep trace lengths shortClose to load returnz Helps minimize transient currentsin the ground planein the ground planeValuesz Individual circuit performanceMaintains low AC impedancez Maintains low AC impedancePower Supply Bypassing B i i ti l tBypassing is essential tohigh speed circuitperformanceCapacitors right at powerCapacitors right at powersupply pinsz Capacitors provide low ACimpedance to groundP id l l h t fz Provide local charge storage forfast rising/falling edgesKeep trace lengths shortClose to load returnClose to load returnz Helps minimize transient currentsin the ground planeValuesz Individual circuit performancez Maintains low AC impedancez Multiple resonancesPower Supply Bypassing B i i ti l t hi hBypassing is essential to high speed circuit performanceCapacitors right at powersupply pinssupply pinsz Capacitors provide lowimpedance AC returnProvide local charge storage forz Provide local charge storage forfast rising/falling edgesKeep trace lengths shortClose to load returnz Helps minimize transient currentsin the ground planeValuesz Individual circuit performancez Maintains low AC impedancez Multiple resonancesFerrite beadsThe World Leader in High Performance Signal Processing SolutionsParasiticsParasiticsPCB parasites take the form of undesired capacitors PCB parasites take the form of undesired capacitors, inductors and resistors embedded within the PCBParasitics are extremely difficult to remove from a PCB Prevention is the best method to minimize parasiticsTrace/Pad CapacitancedAdkA C 3.11=K = relative dielectric constantA iA = area in cm 2Trace/Pad CapacitanceTrace/Pad CapacitanceApproximate Trace InductanceAll dimensions are in mmAll dimensions are in mmApproximate Trace InductanceAll dimensions are in mmExampleL= 25.4mmW = .25mm()H = .035mm (1oz copper)Strip Inductance = 28.8nHAt 10MHz Z L 1.86 Ωa 3.6% errorAt10MHz Z=1.86a3.6%errorin a 50ΩsystemApproximate Trace InductanceAll dimensions are in mmExampleL= 2.54cm =25.4mm Minimize Inductance 1)Use Ground planeW = .25mmH = .035mm (1oz copper)1) Use Ground plane2) Keep length short (halvingthe length reducesi d b44%)() Strip Inductance = 28.8nHAt10MHz Z=1.86a3.6%errorinductance by 44%) 3) Doubling width only reduces inductance byAt 10MHz Z L 1.86 Ωa 3.6% errorin a 50Ωsystem11%Via ParasiticsVia Cross SectionD 2T&HDD 1Capacitor Parasitic ModelResistor Parasitic ModelLow Frequency Op Amp SchematicHigh Speed Op Amp Schematic/en/design-tools/dt-multisim-spice-program-download/design-center/index.htmlHigh Speed Op Amp SchematicParasitic CapacitanceStray Capacitance Simulation SchematicFrequency Response with 2pF Stray Capacitance1.8dB peaking1.8dB peakingStray InductanceParasitic InductanceParasitic Inductance Simulation SchematicAD805525.4mm x .25mm” =29nHPulse Response With and Without Ground Plane0.6dB overshootTransient Response AD80091GHz Current Feedback AmplifierR F 402Ω+5V R G 5V 10uF 402Ω0.1uF 0.1uF 150Ω10uF -5VSmall Changes Can Make a Big Difference!Circuit ACi it A Circuit BCi it BImproper Use of Scope Probe Ground ClipEffect of Clip Lead InductanceProper Grounding for Scope Probe in High-Speed MeasurmentsSmall Changes Make Big Differences Circuit ACircuit B21ns17ns25% reduction in ringing duration and amplitudeThe World Leader in High Performance Signal Processing SolutionsGround and Power PlanesGround and Power Planes Provide A common reference pointShieldingLower noiseLower noiseLower resistancepLower impedanceReduces parasiticsHeat sinkPower distributionGround PlaneIIGround Plane and Trace RoutingGround Plane and Trace Routing。