Logic Design for Array-Based Circuits

by Donnamaie E. White

Copyright © 1996, 2001, 2002 Donnamaie E. White

 

Power Considerations

Last Edit July 22, 2001


CMOS and BiCMOS Arrays

BiCMOS arrays will simplify the computation since they will only compute DC power for the bipolar interface macros. Note that BiCMOS arrays still have an overhead current

CMOS arrays emphasize AC power components and do not usually have DC components listed

When Power is Specified Rather then Current

Another variation in the computational method occurs when the macros are individually specified with a power dissipation, i.e., use this macro - dissipate this much power. The worst-case multiplier and the worst-case voltage may or may not be accounted for in the computation. Only addition is required to compute the macro power dissipation

An overhead component for the bias circuitry may need to be computed and added to the macro sum. If typical power is specified, a worst-case multiplier or adjustment factor may be provided as previously discussed

Design Rules when Power is to be Estimated

  • Before trying to estimate power, verify that the specifications made for the macros are clearly understood

  • Review the overhead (bias) current and how it is handled by the array

  • Review the procedures specified by the particular array vendor for that array series since procedures may vary from series to series with the same vendor

  • Review other vendor-identified power dissipaters - TTL IOEF, ECL static output


AC Macro Power Dissipation

To compute the AC power for any array, perform the computation shown earlier and repeated here:

PAC = 0.20 * ( a * f * G )

where

  • a is the power constant in microwatts/gate-MHz,
  • f is the switching frequency
  • G is the number of gates.

There will be some variation in the form of the equation depending on the use of gates or macros or outputs as the sizing measure. There will be variation depending on the use of a register ratio and there will be variation in the types of macros for which AC power will be computed.

 

Copyright @ 2001, 2002 Donnamaie E. White, White Enterprises
For problems or questions on these pages, contact dew@Donnamaie.com