Logic Design for Array-Based Circuits
Copyright © 1996, 2001, 2002 Donnamaie E. White
Last Edit July 22, 2001
Design To Reduce Power
Power dissipation is controlled by the number and type of macros chosen. . Some of the variations are summarized in Table 4-8.
Table 4-8 Power And Macro Choices
When the array library has options, the high-speed macros will dissipate more current than the standard option macros. The low-power macros are slower with less current than the standard option macros. Driver macros use more current than non-drivers, while super-drivers may use 2-3 times the current used by a driver that can handle fewer loads.
High-functionality macros are using more of the components in a macro cell so the cells these macros occupy use more current. MSI macros are usually pre-placed to avoid hot-spots and to maintain their timing speci-fications.
Some arrays (such as the AMCC Q5000 Series) offer a power-down feature if a macro output is unused. The newer  Q20000 Series does not have this feature.
For DC power dissipation, overhead current is also a factor. Overhead current is that current that is used when an unpopulated array is plugged into the power supplies. It supplies the internal voltage regulators and reference generators. It is a function of the I/O mode and the power supply configuration.
AC power dissipation computations depend heavily on the switching frequency of the various macros. Depending on the vendor, the number of outputs on the macro is a factor in the AC power equation. If one output is required and the other terminated, the terminated output contributes to the AC power equation. When several variations of a macro exist, and there is a choice, use the macro with a single output if that is what is needed.
The DC power computation can be performed by software supplied by the array vendor. AC power computations are still primarily a manual estimate. (Hardware emulators are in the early stages of AC computation support. Refer to the chapter on power computation.)
Figure 4-5 Optimization - Power Considerations