EPE301C Course 1 Practice Test

Dynamic power is roughly proportional to which factors?

Voltage and temperature. Frequency, capacitance, and voltage squared. Leakage current and idle time. Material properties.

Correct Answer:

Frequency, capacitance, and voltage squared.

Explanation:

Dynamic power in a digital circuit comes from charging and discharging the load capacitances as signals toggle. Each switch to the supply voltage stores energy roughly E ≈ 1/2 C V^2 in the capacitive load. If the circuit toggles f times per second, the average power spent on these transitions is proportional to the energy per transition times the switching rate, P_dyn ∠ f × C × V^2 (with an activity factor to reflect how often the node actually switches). So the power grows with how often the circuit switches (frequency), how much capacitance must be moved (capacitance), and the square of the supply voltage (voltage squared). The other choices point to static leakage, idle time, or material factors, which don't capture this primary relationship.

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