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,GNDTrace
PHYSICAL DESIGN AND DEBUGGING
5V
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5V
231732i11-3
Figure 11-3. Orthogonal Arrangement
systems. This capacitor
is
typically placed at the supply's entry point to the board.
It
should be an aluminum
or'
tantalum-electrolytic type capacitor having a low equivalent
series capacitance and
low
equivalent series inductance. The capacitance value
is
typi-
callylO to
47
JlF.
An additional
0.1
JlF
capacitor may be needed if supply noise
is
still a
problem.
A second type of decoupling
is
used for the rest
of
the ICs on the board. Additional
decoupling capacitors can be used across the devices between
Vee
and V ss lines. The
voltage spikes that occur due to switching of gates are reduced because the extra current
required during switching
is
supplied
by
the decoupling capacitors. These capacitors
should be placed close to their devices since the -inductance of lengthier connection
traces reduce their effectiveness.
11-6