CPUs and architecture

In a CMOS circuit, if only the supply voltage is halved with everything else unchanged, what happens to dynamic power consumption?

  1. AIt does not change
  2. BIt halves
  3. CIt becomes one quarter
Show answer and explanation

Answer: C. It becomes one quarter

Dynamic power in CMOS circuits is P = α C V² f (α: activity factor, C: load capacitance, V: supply voltage, f: frequency), proportional to the square of the supply voltage. Halving the voltage reduces power to one quarter. Lowering voltage is therefore the most effective way to save power, but it reduces operating speed.

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