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! |
