01-01-2013, 11:58 AM
Crosstalk
Crosstalk.ppt (Size: 461 KB / Downloads: 27)
Mutual Inductance and Capacitance
Crosstalk is the coupling of energy from one line to another via:
Mutual capacitance (electric field)
Mutual inductance (magnetic field)
Mutual Inductance and Capacitance “Mechanism of coupling”
The circuit element that represents this transfer of energy are the following familiar equations
The mutual inductance will induce current on the victim line opposite of the driving current (Lenz’s Law)
The mutual capacitance will pass current through the mutual capacitance that flows in both directions on the victim line
Crosstalk Induced Noise
“Voltage Profile of Coupled Noise”
Near end crosstalk is always positive
Currents from Lm and Cm always add and flow into the node
For PCB’s, the far end crosstalk is “usually” negative
Current due to Lm larger than current due to Cm
Note that far and crosstalk can be positive
Creating a Crosstalk Model
“Transmission Line Matrices”
The transmission line Matrices are used to represent the electrical characteristics
The Inductance matrix is shown, where:
LNN = the self inductance of line N per unit length
LMN = the mutual inductance between line M and N
Odd and Even Transmission Modes
Electromagnetic Fields between two driven coupled lines will interact with each other
These interactions will effect the impedance and delay of the transmission line
A 2-conductor system will have 2 propagation modes
Even Mode (Both lines driven in phase)
Odd Mode (Lines driven 180o out of phase)
The interaction of the fields will cause the system electrical characteristics to be directly dependent on patterns