Design Optimization
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
Macro Options That Affect Power Consumption |
Macro Option, if available |
Macro Drive capability |
Functionality |
Outputs used or terminated |
I/O mode |
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 [1994] 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
![](/book/0127466606/CHAP_4/ASFig4-5.JPEG)
Optimization Issues - Power
|