
Basic Design Rule for Advanced PCB (1)
1. High speed current path
Load
Current
trace
Load
Current
trace
High-speed
Return current
Stays tightly
bunched under
Signal trace
Driving gate
Driving gate
At low frequency current,
follows the path of least resistance
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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
Return current
I.C.
I.C.
Signal trace
Hole clearance on
ground plane
Signal trace
Equivalent circuit showing inductance
in the return path. This inductance is
approximately 1nH/cm.
Return current
on ground place
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
Basic Design Rule for Advanced PCB (3)
3. Trace 3W rule
Signal trace
w
w
Via
w
w
w
w
w
w
Ground Plane
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
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
Basic Design Rule for Advanced PCB (4)
4. Inductive & Capacitive Cross-talk
Vs
Zo
Zo
Zo
source
victim
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
Basic Design Rule for Advanced PCB (5)
5. Concept of transmission line
Trace width
Micro strip trace
Copper
thickness
Dielectric
h
Copper plane
Dielectric
thickness
C
PCB laminate
Plane
Micro-strip
Plane
Plane
Dielectric
Signal layer
Dielectric
Signal layer
Signal layer
Plane
Plane
Dual Strip-line
Strip-line
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
Basic Design Rule for Advanced PCB (6)
6. Conclusion
• 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)
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