=0pt
2=HE2
by =
7=8=18 by 1000 7 by8
=.001by 7 1= 1.051
=-2 -12112=-1000pt target of the model developed here is to
offer limited estimation errors with respect to physical SPICE
simulations and to improve the computation speed of more than one
order of magnitude. This could be useful in optimization algorithms.
Thus the aim of the model is to evaluate the delay and power
dissipation of CMOS structures.
Several approaches have been used to evaluate the delays of CMOS
structures:
some models are derived from SPICE simulations
by means of look-up-tables [5]; some are analytical
[6] while others approximate the evaluation of the
delay with step or ramp inputs
[7,8,9,10,11].
Regarding the power consumption the main contributions are:
switching power, short circuit current and sub-threshold conduction.
The first one occurs during the charge and discharge of internal capacitances;
short circuit current originates from the simultaneous
conduction of p and n networks and it is dominated by the slope
of node voltages;
sub-threshold currents are due to the weak inversion conduction
of MOSFETs and become relevant when the power supply
is scaled in sub-micron technologies.
Most of the proposed power models use estimation algorithms not compatible with the delay analysis. The purpose of the FAST model is to combine delay and power evaluations in the same estimation procedure, allowing the simultaneous optimization of delay and power.
The section 3.1 reports the theory behind the FAST
model, and in particular: §3.1.1 shows the MOS
equations used in the model, §3.1.2 shows the internal nodes
voltage approximation made by the model and §3.1.3 explains how
the threshold voltage variation are taken into account in the model.
Section 3.2 shows how the FAST model estimates the
delay, and in particular §3.2.1 shows how the equation are
solved; while section 3.3 reports the method used for
the calculation of the power consumption, and in particular
§3.3.1 accounts for the switching power,
§3.3.2 accounts for the short-circuit power,
and §3.3.3 accounts for the subthreshold power.
Finally the section 3.4 presents some results by the
comparison of the model with HSPICE and the
section 3.5 draws some conclusions.