Civil Engineering Reference
In-Depth Information
4.5.2
Miller capacitance models
A simple way to model crosstalk capacitances is to replace the coupling capac-
itor by a Miller capacitance to ground. To see how one can arrive at the value
of this Miller capacitor‚ let us consider three cases‚ shown in Figure 4.13:
a.
When a wire switches and is next to a nonswitching (silent) neighbor‚ the
value of the Miller capacitance to ground equals the coupling capacitance.
Although the silent wire will see a small noise bump on its voltage wave-
form‚ the time constant associated with this is large‚ so that the across
the capacitor is substantially determined by the aggressor. Therefore‚ the
the value of across the coupling capacitor and the Miller capacitor are
identical‚ so that the
contribution of the former is well captured by the
latter.
b.
When the aggressor and the victim switch in the same direction‚ if the
switching events track each other perfectly‚ then the value of across the
coupling capacitor is zero. Using this intuition‚ the Miller capacitor is simply
set to zero‚ which results in the same
current injection into the wire as
from the coupling capacitor.
c.
When the aggressor and the victim switch in opposite directions‚ if the
changes on the two wires are symmetric‚ then will be twice that for
case This may be modeled by using a Miller capacitor value that is
twice the value of the coupling capacitance.
The above cases are based on simplistic assumptions‚ and practically‚ for a
coupling capacitance of instead of a approximation‚ more realistic
scenarios are “fudged” in using a approximation instead. This is
not a completely unreasonable approximation‚ and has been shown to be exact
under a specific coupling model in [CKK00].
Although Figure 4.13 simplistically shows the lines coupled through a single
coupling capacitor‚ the same reasoning is valid even for segmented coupled
RC lines‚ such as that shown in Figure 3.8. In such a case‚ the coupling
