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Winter 2005

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Title: Slide 1 Last modified by: Chuck Klein Created Date: 1/2/2003 10:41:06 PM Document presentation format: On-screen Show Company: The Ohio State University – PowerPoint PPT presentation

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Title: Winter 2005


1
Grounding
  • Grounds
  • Common reference for the circuit
  • Safety
  • What is the potential problem of grounding?
  • Improper grounding may induce noise on the
    transmission lines

2
Grounding
  • Problem Faradays Law of Induction
  • ?Avoid ground loops

3
Spatial Dependence
Within a cabinetvs. Between two buildings
4
Shielding Techniques
Relative voltages inside themetal box are always
equal
Connect the shield to the signal ground to reduce
feedback effects induced by the shield.
5
Where to Ground the Shield?
Shield should be connected to the earth ground at
input reference.
What if we interconnect twodevices in different
buildings?
6
Long Paths
  • Problem Two distant, connected chassis grounded
    at different points may carry large currents?
    Break the chassis connection
  • Solutions
  • Use larger signals to increase SNR
  • Use light as medium
  • Fiber optic link
  • Optical isolators (phototransistor and LED in a
    pack)
  • Use balanced (double-ended, differential)
    connections

7
Balanced Connections
  • Both chassis are isolated electrically
  • Noise induced on both lines
  • Signal carried on each line s(t) and s(t)
  • Differential mode gain
  • Common mode gain
  • Differential mode gain gtgt common mode gain

8
Crosstalk due to Bad Grounds
Resistance of bad ground
Ideal
Model of Actual
9
UTP Revisited
  • Faradays Law of Induction
  • Direction of the induced current
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