Signal Dispersion
♦Constant time delay is necessary to ensure that signals arrive undistorted at the destination
Revision 4 |
Copyright Telephonics 2002-2005 |
39 |
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Signal Dispersion Example
♦Eye Diagram
♦4.8 Gbps
♦36” trace length
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Er 4 |
FR4 |
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RO4350 |
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3 |
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100 |
1000 |
2000 |
10000 |
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Frequency in MHZ |
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Revision 4 |
Copyright Telephonics 2002-2005 |
40 |
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Mitigation of Dispersion
♦More Stable Dielectric
-Option for new designs
♦Pre-Emphasis Filter
-Option for new designs or design upgrade
♦Equalizer
-Option for new designs or design upgrade
-Maxim MAX3784 (40” length, 6 mil, FR4, 5 Gbps)
Revision 4 |
Copyright Telephonics 2002-2005 |
41 |
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Coupling
♦Traces run in close proximity will couple
♦Coupling is determined by geometry
-trace separation, distance to ground(s) & parallel length
-peaks at λ/4 and below λ/4 slope is 20 dB/decade
30
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Notes: |
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1. |
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Material FR4, εr = 4.5 |
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2. |
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Parallel length = λ/4 = 1.39” at 1 GHz |
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Revision 4 3. |
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Trace height = 1.4 mils |
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Copyright Telephonics 2002-2005 |
42 |
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