Thanks for the clarification.


______________________________ Reply Separator _________________________________

>I'm not sure I understand your concern about the impedance 
>"between" a pair of traces. Each trace has its own impedance. For a 
>differential pair, you would need to match those impedances, as 
>well as other characteristics such as delay.
     
>No it does not matter if one plane is "hot" and the other is ground. 
>That is a DC definition. At high frequency, the power plane is just 
>another ground plane, and is an additional path for a high-speed 
>return signal. The capacitance between the planes does provide some 
>lead inductance decoupling
     
  > Does anyone out there have the preferred configuration and equations   
  >for controlling the impedance between a differential pair of traces     
  >that are sandwiched between two power planes on epoxy-glass?
  > 
  > Also, does it matter if one of the power planes is ground and the      
  >other "hot", or will the inevitable in-circuit capacitance between them 
  >ensure a common ac reference at typical transmission line frequencies?
  > 
     
     Max.P.Harris
     Lockheed Martin Canada, Inc.

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