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[Signal]  Transmission Lines

Introduction
As digital gets faster and faster, it starts to look more like analog than digital. It is necessary to have a good understanding of the Analog/RF like properties of fast digital. Attention must be paid to such things as Transmission Line effects like: impedance matching, series and parallel termination, microstrip layout; propagation of very high frequencies to and from the circuit; crosstalk, proper bypass, decoupling, shielding techniques, as well as ground plane design. 

Because of the speed of this demand  (nsec) the frequencies are in the many hundreds of MHz. And, any conductor/wire between the gate power pin and the power source can look like an unacceptable high resistance (.....). 
In the world of fast edge sensitive logic, it is a simple matter to conceive of "inappropriate communications" between logic elements through the power rail. 

Going back to basics: the definition of a voltage source is that it has Zero Impedance out! If you could enforce that definition at the power pin of every logic element, then life as we know it, would be GOOD! 

The Effects of Termination Values on Reflection
Termination Responses in Transmission Lines
(A) Zt = ZL,  (B) Zt = open,  (C) Zt = short
TOP /\
Power Distribution in Standing Waves

Transmission Line Demonstration Setup

Demonstration Setup to show the Effects of Taps (Drops) on Transmission Line Signals

 


 

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