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in Fig-1 it is shown as Level-1. This is computed using the formula in Eqn-1
by assigning L 1 . 1
in 1 =0 and L 1 . 1
in 2 = 0 since they are primary input nets. Hence
L 1 . 1
out = 1. The same formula can be applied progressively to determine rest of
the levels.
a
sum
1.1
2.1
b
c
2.2
carry
3.1
1.2
Level-1
Level-2
Level-3
Fig. 1. Group of gates leveled based on the circuit depth
3.2 Power Estimation Methodology
The proposed methodology estimates the maximum instantaneous power by de-
termining the maximum activity among the activity at each levels of the circuit.
Mathematically this can be expressed as follows.
P peak = Max ( A l )
(2)
where P peak is the estimated worst peak power and A l is the maximal activity
at l th level of the circuit. Detail is explained in the following section, Section 4.
4 Background on Binary Integer Linear Program
Binary integer linear programing(BILP) is a class of optimization method called
linear programing(LP) method. In BILP the variables are constraint to take only
0 or 1 value-a binary digit. The BILP problem is to optimize a given function
called objective function subject to a given set of constraints. The general form
of BILP can be stated as follows:
Minimize : f ( x ), Subject to : Ax =0, x [0 , 1]
In our earlier work[10] we have explored the BILP method to maximize the
toggle activity subject to functionality constraints. Summary of the method is
presented in Table 1.
 
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