Power Management

How does leakage power change as chip temperature rises, and what problem can result?

  1. AIt rises steeply (exponentially) with temperature, possibly causing a vicious cycle of more heat and higher temperature (thermal runaway)
  2. BIt falls as temperature rises, so hotter means more efficient
  3. CIt is constant regardless of temperature
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Answer: A. It rises steeply (exponentially) with temperature, possibly causing a vicious cycle of more heat and higher temperature (thermal runaway)

Subthreshold leakage rises steeply with temperature because the energy distribution of carriers broadens, and it can increase substantially with roughly every 10°C. More leakage means more heat, higher temperature and still more leakage, a positive feedback loop that can lead to thermal runaway if cooling is insufficient. Temperature sensors therefore monitor the chip and controls such as lowering frequency are applied.

  • A. Correct. Cooling design must account for it.
  • B. It increases instead.
  • C. It depends strongly on temperature.
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More Power Management questions

  1. Which describes power gating?
  2. Which correctly pairs a caveat of power-gated blocks with its countermeasure?
  3. Which correctly compares clock gating and power gating?
  4. In power gating, why are a block's power switches often turned on gradually in sequence rather than all at once?
  5. What is the role of the isolation cells placed between a powered-off block and running blocks?