Which expression gives the figure of merit of a digital IC?
2021
Which expression gives the figure of merit of a digital IC?
Answer: C. Propagation delay time × power — ConceptFor a digital logic family, the power-delay product (PDP) is the energy-related figure of merit. It is defined abstractly as average power dissipation…
- A.
Propagation delay time − power
- B.
Propagation delay time ÷ power
- C.
Propagation delay time × power
- D.
Propagation delay time + power
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Show answer & explanation
Correct answer: C
Concept
For a digital logic family, the power-delay product (PDP) is the energy-related figure of merit. It is defined abstractly as average power dissipation P multiplied by propagation delay tp: PDP = P × tp. A lower PDP represents less energy used per switching event under the stated measurement convention.
Application
The expression formed by multiplying propagation delay time and power dissipation has exactly the PDP form.
Cross-check and contrast
tp − P and tp + P combine quantities with unlike dimensions, so neither sum nor difference defines a physical figure of merit.
tp ÷ P has units of seconds per watt, not energy.
tp × P has units W·s = J, which is the energy dimension associated with a switching event.
Result
Therefore, the required relation is propagation delay time × power dissipation.