Power Management
As supply voltage is lowered, total energy per operation reaches a minimum at some voltage and then rises if voltage is lowered further. Why?
- ABelow that point circuits become so slow that leakage energy accumulated during each operation grows faster than dynamic energy shrinks
- BLowering voltage increases dynamic energy
- CLowering voltage increases the number of transistors
Show answer and explanation
Answer: A. Below that point circuits become so slow that leakage energy accumulated during each operation grows faster than dynamic energy shrinks
Dynamic energy falls with the square of voltage. Leakage energy, however, is leakage power times the time per operation, and as voltage drops circuits slow and that time grows rapidly, so leakage energy rises sharply below some voltage. The voltage minimizing their sum is the minimum energy point, often near or slightly below the threshold voltage.
- A. Correct. That minimum is called the minimum energy point.
- B. Dynamic energy falls as voltage drops.
- C. The transistor count does not change.