Editing Register-transfer level (section)

====Example====
G<sub>i</sub> denoting the hardware complexity of the multiplier is related to the square of the input word length i.e. N<sup>2</sup> where N is the word length. The activation frequency is the rate at which multiplies are performed by the algorithm denoted by <math>f_{mult}</math> and the PFA constant, <math>K_{mult}</math>, is extracted empirically from past multiplier designs and shown to be about 15 fW/bit2-Hz for a 1.2&nbsp;μm technology at 5V.
The resulting power model for the multiplier on the basis of the above assumptions is:<br />
<div style="text-align: center;">
<math>\displaystyle P_\text{mult} = K_\text{mult} N^2 f_\text{mult}</math>
</div>

'''Advantages:'''
* Customization is possible in terms of whatever complexity parameters which are appropriate for that block. E.g. for a multiplier the square of the word length was appropriate. For memory, the storage capacity in bits is used and for the I/O drivers the word length alone is adequate.

'''Weakness:''' 
* There is the implicit assumption that the inputs do not affect the multiplier activity which is contradictory to the fact that the PFA constant <math>K_{mult}</math> is intended to capture the intrinsic internal activity associated with the multiply operation as it is taken to be a constant.

The estimation error (relative to switch-level simulation) for a 16x16 multiplier is experimented and it is observed that when the dynamic range of the inputs does not fully occupy the word length of the multiplier, the UWN model becomes extremely inaccurate.<ref>[http://delivery.acm.org/10.1145/270000/266171/p365-gupta.pdf?ip=103.27.8.42&id=266171&acc=ACTIVE%20SERVICE&key=045416EF4DDA69D9%2EF8E7F338DF557316%2E4D4702B0C3E38B35%2E4D4702B0C3E38B35&CFID=504808115&CFTOKEN=79046804&__acm__=1429710436_686f8f2ffb085b129fe587723a6ee130 "Power Macromodeling for High Level Power Estimation"]</ref> Granted, good designers attempt to maximize word length utilization. Still, errors in the range of 50-100% are not uncommon. The figure clearly suggests a flaw in the UWN model.