Power Considerations
Last Edit July 22, 2001
Design Rules for Power Reduction (AMCC)
- Check the library for either power-down of unused outputs or the
existence of different output pin versions of the macros. Examine both
power and speed differences of these versions
- Minimize the number of terminated outputs
- When a version of a macro is absent from the library, the array vendor
may be able to supply a custom macro or an alternate design solution.
Do not hesitate to consult the array vendor.
Unused Inputs - Bipolar, BiCMOS
Macros with unused inputs may be dissipating more current than is required
for the function being performed. When too many macro inputs are grounded
(global ground) or clipped to VDD or VSS, a check should be made to see
if another macro could be used that more closely reflects the circuit
requirements
MSI And High-Functionality Macros
Dense bipolar macros, as represented by the AMCC MSI macros and any complex
chip-efficient macro in any other libraries, represent high-power. They
concentrate operations in a small chip area. Their placement in a bipolar
array may need to follow row and quadrant current limits. In their favor,
their use reduces the number of macros needed to implement a function
but the overall current usage may or may not be reduced
BiCMOS MSI macros are generally spread out over a larger number of cells
than their bipolar counterparts and do not require the same power considerations
Driver macros on bipolar arrays supply high-drive capability in a small
chip area and have the same potential restrictions as for the bipolar
MSI macros. The bipolar array may have internal current limits that need
to be honored. Drivers reduce the number of other macros that would be
required but their use may increase the overall power required by the
circuit. High-fan-out drivers were specifically developed for use in clock
distribution schemes
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