Electronics Forum / CAD / January 2005

I assume you mean calculate and not measure.  If you really want to
measure it you need to build one.

If you want to calculate it, you need to get a completed design ready as
though you were going to put it into real silicon.  A lot of CPLD and FPGA
tools contain a power estimator.

How many parts are in the design?  Are you doing it transistor by
transistor?

www.linear.com has an unlimited spice on its web site.  It is called
SwitcherCad-III for historical reasons.  You could feet it your schematic
or netlist and let it run until you get an answer.  Computer time is cheap
these days.

Hello Chris,
a multiplier may have many very similar circuit blocks.
You simply calculate the power dissipation of one block and
assume that N-blocks require N-times that power.

Another approach is trying to calculate how many transition
you have per multiplication. If you know also how many gates
are conencted to those nets, then you can make a good estimation
about the power dissipation. The power dissipation for one
net is U^2*C*f plus some additional power in the transition.
The power dissipation of a single gate could be simulated with
SPICE for this approach.

A serial multiplier may have only a few thousend transistors.
You should give HSPICE or LTSPICE a try.
LTSPICE is a free and powerful SPICE simulation program.
www.linear.com  SwitcherCADIII/LTspice

Best Regards,
Helmut

I'm not that familiar with HSpice anymore.  Quite a few years ago,
when I last used it, I found it to have the worst GUI ever conceived
by man ;-)

However, try this:

Display "I(VDD)"... you will see lots of current spikes.

Then (this works with PSpice, don't know about HSpice):

Display "avg(I(VDD))", since VDD is a constant, this display
multiplied by VDD will be your average power, or HEAT.

                                       ...Jim Thompson

           
I love to cook with wine.      Sometimes I even put it in the food.