PCB Design for 1 Gbps. ECE 4006 Dr Brooke. Overview. What signals are being routed? How can you route those signals? How to apply routing to PCB? PCB design techniques. Signals being routed. High Frequency Sensitive Analog (e.g., IN from PD)
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PCB Design for 1 Gbps
ECE 4006
Dr Brooke
1 wavelength =
= 20 cm @ 500 MHz,
EM wave
¼ wavelength or greater = transmission line = 5 cm
1/10 wavelength or less = wire = 2 cm
Square Wave = 1st + 3rd + 5th … Harmonics
Using up to 5th harmonic has eye closure ~15%
Using up to 3rd harmonic has eye closure ~30%
Using only 1st harmonic has eye closure ~50%
First Harmonic = 1/10 * 20 cm = 2 cm
Second harmonic (present in real data) = 2 cm / 2 = 1 cm
Fifth
Harmonic
= 4 mm
Third
Harmonic
= 6.7 mm
Fourth
Harmonic
= 5 mm
For Gigabit Ethernet
50 ohms
Signal arrives after transmission delay.
“sees” 50 ohms immediately
between core and shield
- nothing else if terminated properly
- “echo” after 2 x transmission delay otherwise
+
+OUT
100 ohms
GND
-OUT
+
“sees” 50 ohms immediately
between core and shield
“sees” 50 ohms immediately
between core and shield
Balanced = equal and opposite
That is for AC components:
(+OUT) = -(-OUT)
45 deg
45 deg
1/10th wavelength
1/10th wavelength
VCC
OUT
Load
VEE
“Decoupling
Capacitor” –
Must be a “short” at signal frequency
ground path – minimum length!