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Basic Design Rule for Advanced PCB (1)

1. High speed current path

Load

Driving gate

Current trace

At low frequency current, follows the path of least resistance

LoadCurrent

trace

Driving gate

High-speedReturn currentStays tightlybunched underSignal trace

At high frequency current,follows the path of least inductance

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Basic Design Rule for Advanced PCB (2)

2. Induction of slot on Ground plane

I.C. I.C.

Return current

Signal trace

Hole clearance onground plane

Equivalent circuit showing inductancein the return path. This inductance isapproximately 1nH/cm.

Signal trace

Return current on ground place

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Basic Design Rule for Advanced PCB (3)

Signal trace

Via

ww

ww ww ww

3W 3W

3W rule is to minimize coupling between trace and signals by providing“clean path” and by aligning the signal flux and the return flux.

☞Minimize RF fringe between traces☞Reduce cross-talk between traces without ground guards

Ground Plane

3. Trace 3W rule

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Basic Design Rule for Advanced PCB (4)

4. Inductive & Capacitive Cross-talk

Vs Zo

source

victim

Zo Zo

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Basic Design Rule for Advanced PCB (5)

5. Concept of transmission line

Trace width

Copperthickness

Dielectric

Copper planeDielectricthickness

h C

Micro strip trace

PCB laminate

Plane

Micro-strip

Plane

Plane Plane

Plane

DielectricDielectricSignal layer

Signal layer

Signal layer

Strip-line Dual Strip-line

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• High speed PCB design requires consideration of:

– Signal Propagation (Ringing & Reflection),

– Interaction between signals

(Cross-talk, Electro-Magnetic Interference)

• High Speed PCB performance needs:

– To select suitable material (FR-4, BT, Polyimide, …)

– Good process control :• Stack up of layers, especially for multi layers• Uniform and stable impedance (R, L, C)

Basic Design Rule for Advanced PCB (6)

6. Conclusion