# Power Considerations

Last Edit July 22, 2001

## Case Study: AC Power Computation

The Q20000 Series AC power methodology [as of 1994] is detailed below to allow sample computations and to provide some reference for analysis of other arrays.

Step 1: Build the Macro Occurrence Table

A macro occurrence worksheet for interface and internal logic macros can be constructed before design capture to assist in the computation of total circuit power dissipation. A macro occurrence worksheet for the interface and internal logic should provide:

• A list of the different macros differentiated by option;
• The number of times each macro appears on the schematics;
• The number of outputs the macro has.

The macros are differentiated by option if there is a difference in the conversion constant. The number of outputs is required if that is the sizing measure used by the vendor. If the number of gates rather than the number of macros is required, a conversion factor in gates per macro is supplied.

The AMCC MacroMatrix ERC produces a BiCMOS/Bipolar Power Computation Worksheet that lists macros and their occurrences and which can be used for manual AC power analysis.

Because of the use of several different conversion constants for the Q20000 macros, the macros on the worksheet must be grouped within certain types. The types are ECL Darlington outputs, ECL inputs and internal macros. Other ECL outputs are not involved in the computation. TTL I/O macros are not involved in the computation.

Step 2: Find the number of Darlington Outputs

Using the macro occurrence worksheet, find the number of Darlington outputs. For AMCC customers, the number of Darlington outputs can be determined from the AMCC I/O statistics ERC report and from the AMCC AC Bipolar/BiCMOS Macro Occurrence worksheet.

Count the number of Darlington output macros switching at the fastest frequency. Count the number of Darlington output macros switching at the next fastest frequency. Repeat until all Darlington output macros are accounted for.

Step 3: Compute AC Power For all ECL Darlington Output Macros

Using the counts from step 2, compute the AC power dissipated by the ECL Darlington outputs used in the circuit. For AMCC arrays, use:

PacDARoutputs = f * n * 15 microwatts

where
f = maximum frequency of the Darlington outputs in MHz
n = number of ECL Darlington output macros toggling at frequency f
conversion factor = 15 microwatt/macro-MHz for Q20000 Series

• Compute the AC power due to those macros switching at the fastest frequency.
• Compute the AC power due to those macros switching at the next fastest frequency.
• Repeat until all Darlington output macros are accounted for and sum the results.

Step 4: Find the Number of ECL Inputs

Using the macro occurrence worksheet, find the number of ECL input macros. For AMCC customers, the number of ECL input macros can be determined from the AMCC I/O statistics ERC report and from the AMCC AC Bipolar/BiCMOS Macro Occurrence worksheet.

• Count the number of ECL input macros switching at the fastest frequency.
• Count the number of ECL input macros switching at the next fastest frequency.
• Repeat until all ECL input macros are accounted for and sum the results.

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