1. Optimize the architecture for low power
Earlier you optimize your design for power it is better and more effective. You can optimize the architecture in many ways. You can optimize the type, size, frequency and bus width of memory. Consider routing resources to be used and effect of loading while deciding bus grouping. As the wire delays play a major role in deep submicron era, minimize the global signals. Consider operating device in low power modes whenever feasible.
2. Reduce the voltage
As shown in the expression impact of Voltage on power is quadratic. It reduces the speed of the design too. Decide which voltage gives optimum speed. There can be multiple voltage rails for different parts of the design. Take care the timing at the interface of multiple voltages. This is a very effective method to control power and widely used.
3. Reduce the switching activity
Since all blocks of the design needn’t be active all the time, we can reduce the average power of the chip by gating the clock for the inactive parts. This method is very effective when the chip has multiple blocks and only few will be active at a time or when off time of the chip is significant. This is a traditional method used in earlier technologies too. Simplicity is at its best here. Partitioning the logic to suit this style can make this very effective.
4. Reduce the glitches
Unwanted transitions play a major role in power consumption. This is mainly so, if the combinatorial logic is too deep. You can minimize this by prioritizing the signals such that transitions can be minimized. Proper design practices or ground rules can be helpful. Some time, even slow gates can make the difference.
5. Control the rise and fall time of the important signals
Some signals in the design may be not critical for the timing. Still make sure they are not overloaded, such that transition time can trouble.
6. Reduce the number of global signals
Global signals are always a problem. They need to be addressed for the timing. Since the wire capacitance plays a major role when technology shrinks the minimum size to 90nm and beyond. Optimize inter block communication for low power.
7. Optimize the cells/circuits for low power
This is one of the time tested technique to reduce power. Logic based on pass transistors can be of great help if the design needs repeated data path structures like adders and multipliers. You can optimize the cells for low power and place with minimum wire loading. This can be very effective for structured data path style applications.
8. Reduce the cross talk
New technologies make this a necessity. As the metal walls grow taller and shrink the gap with neighbors, this problem becomes dominant. There are many methods to reduce this and everything need to be analyzed and practiced if you are in 90nm and beyond.
9. Bias the substrate
This is one more area brought to front by deep sub micron era, as leakage power is no more negligible. You can use this to reduce the power when the chip is not operating.
10. Plan, estimate and optimize for power in every stage
Most important rule for low power design is to plan, estimate and optimize the design for power in the every possible stage. At some stage, estimation can be easy using design automation tools. In some other stages, you have to rely on approximates and assumptions. |
