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PHYSICAL DESIGN AND DEBUGGING
[1
0
0
m
0
=0.1
~F
;386 ,.
OX
CPU
~
0
rt]
=1.0
~F
0
~
231732;11·5
Figure 11-5. Decoupling with Surface Mount Capacitors
~o~o
-D-
-tm-
~
=1.0~F
-mJ-
CJ-
;386 ,.
OX
CPU
~
o =0.1
~F
-D-
~
-CJ-
O~O~
231732;11·6
Figure 11-6. Decoupling with Leaded Capacitors
11.4 HIGH FREQUENCY DESIGN CONSIDERATIONS
The overwhelming concern in dealing with high speed technologies
is
the management
of transmission lines. As the edge rates of the signals increase, the physical interconnec-
tions between devices behave like transmission lines. Although transmission-line theory
is
straightforward, the difference between ordinary interconnections and transmission
lines
is
fairly complex. Transmission lines have distributed elements which are hard to
define and designers tend to over compensate for the effects of these elements.
Efficient Intel386
DX
CPU designs require the identification of the transmission lines
over
back
plane wiring, printed circuit board traces, etc. Once this task
is
accomplished,
designer's next concern should
be
to deal with problems associated with electromagnetic
propagation, impedance control, propagation delay and coupling.
11-8