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When applying gating proposed in the above subsection, we
introduce overheads in the controller for generating gating
signals and introduce extra control wires. Such overheads should
be taken into consideration when examining the benefits of gating
a signal to suppress SSA. We adopt a method
from [62] for overhead computation and make
similar assumptions for this purpose. We assume a typical gating
control signal requires 10 gates to generate, a typical one of
such gates has three fanouts, the gate is four times the minimum
gate size, and the switching activity is 0.5. The switched
capacitance, , and area overhead, , in the
controller are estimated as
where is the number of gating control signals,
the input capacitance for a minimum sized gate,
the minimum sized gate area, and the scaling factor
for area overhead is to account for spacing between gates
and the wiring space. Moreover, the switched capacitance overhead
of the gating control signal wires is estimated as
where is the final circuit area, is used as
the average gating control signal wire length, is the
unit-length capacitance for a minimum-width metal-1 wire,
is the frequency of transitions on the gating control signal
wires, and the scaling factor is to account for the fact that
control signal wires are not usually routed as metal-1 or at
minimum width. can be estimated using the profiling and
scheduling information. All the overheads are included in the
results we report later.
Next: Different output network topologies
Up: Reducing Spurious Switching Activity
Previous: Tri-state buffer based technique
Lin Zhong
2003-10-11