Logic Design for Array-Based Circuits

by Donnamaie E. White

Copyright © 1996, 2001, 2002 Donnamaie E. White

 

Power Considerations

Last Edit July 22, 2001


Case Study: DC Power Computation

The Q20000 Series DC power methodology is detailed below to allow sample computations and to provide some reference for analysis of other arrays. The method can be modified to apply to all AMCC arrays, independent of their technology, and to apply to other vendor arrays

Steps Required To Compute DC Power: - Example Array Series

Step 1: Build the Macro Occurrence Table

A macro occurrence table can be constructed before design capture to assist in the manual computation of interface current and power dissipation. A macro occurrence table should provide the data necessary to compute the worst-case DC power dissipated by the circuit. (This table approach can be used with macros that specify current or macros that specify power.)

Macro
Name
Number of Macro
Occurrences
Macro
ICC
Macro
IEE
Total
ICC
Total
IEE

AMCC MacroMatrix ERC power computations are done with the worst-state current value, assuming the worst "state" always for those macros specified with HIGH and LOW or ENABLED and DISABLED current. The power dissipation value computed will be conservative. A manual com-putation can be made to adjust the current used for these state-dependent macros

Identify those macros where some assumption must be made on the value of the current to be used in the table. They will need to be identified during design submission

Step 2: Find the Total Interface Macro Current

The macro current for individual interface macros is multiplied by the number of occurrences to determine the total typical current resulting from the use of that macro in the circuit. Change the labels if power has been specified

Compute the total current used by all occurrences of each interface macro and sum these totals to find the total IEE and ICC interface current

    IinterfaceCC = SUM INTERFACE MACROS ICC CURRENT
    IinterfaceEE = SUM INTERFACE MACROS IEE CURRENT

Unless the circuit uses a single-power supply these two sums must be kept separate

Step 3: Compute the Worst-Case Interface Current

Multiply both sums by the worst-case current multiplier (WCCM1) for the interface macros to obtain the worst-case current due to interface macros

    IinterfaceCCwc = WCCM1 * IinterfaceCC
    IinterfaceEEwc = WCCM1 * IinterfaceEE

The Q20000 Series uses three worst-case current multipliers, one for core macros, one for interface macros and one for overhead current. Other arrays may be specified with one multiplier or may vary the multiplier or adjustment factor based on the product grade

Table 7-12 Example Worst-Case Current Multipliers

Interface Internal Overhead
WCCM1 WCCM2 WCCM3
1.30 1.25 1.25

 

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

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