Buffer Insertion Basics - Computer Engineering & Systems Group ...

(a)
(b)
Figure 7: Illustration of noise model.
The total current induced by the aggressors on e is
t∑
I e = C e (λ j · µ j ) (14)
j=1
Often, information about neighboring aggressor nets is unavailable, especially if buffer insertion
is performed before routing. In this case, a designer may wish to perform buffer insertion
to improve performance while also avoiding future potential noise problems. When performing
buffer insertion in estimation mode, one might assume that: (1) there is a single aggressor net
which couples with each wire in the routing tree, (2) the slope of all aggressors is µ, and (3) some
fixed ratio λ of the total capacitance of each wire is due to coupling capacitance.
Let I T(v) be defined as the total downstream current see at node v, i.e.,
I T(v) = ∑
e∈E T(v)
Ie,
where E T(v) is the set of wire edges downstream of node v. Each wire adds to the noise induced
on the victim net. The amount of additional noise induced from a wire e = (u,v) is given by
Noise(e) = R e ( I e
2 + I T(v)) (15)
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