Power Management

Which describes static (leakage) power in CMOS circuits?

  1. APower that grows in proportion to clock speed
  2. BPower consumed continuously by leakage currents through off transistors and the like, even when signals do not switch
  3. CPower used only when manufacturing the chip
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Answer: B. Power consumed continuously by leakage currents through off transistors and the like, even when signals do not switch

Transistors are not perfect switches; even when off, small subthreshold and gate leakage currents flow. Each is tiny, but across billions of transistors they add up to significant power, which grew more prominent as scaling lowered threshold voltages. Static power does not fall when clocks stop, so it is addressed by cutting supply power itself, for example with power gating.

  • A. Power proportional to frequency is dynamic power.
  • B. Correct. It flows even with the clock stopped.
  • C. It is consumed during operation.
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More Power Management questions

  1. How does leakage power change as chip temperature rises, and what problem can result?
  2. Which describes power gating?
  3. Which correctly pairs a caveat of power-gated blocks with its countermeasure?
  4. Which correctly compares clock gating and power gating?
  5. In power gating, why are a block's power switches often turned on gradually in sequence rather than all at once?