Power Management
In power gating, why are a block's power switches often turned on gradually in sequence rather than all at once?
- ATo avoid a large inrush current charging the block's capacitance all at once, which would sag the supply and make other running circuits malfunction
- BTurning all switches on at once doubles the block's contents
- CSwitches can only be fabricated one at a time
Show answer and explanation
Answer: A. To avoid a large inrush current charging the block's capacitance all at once, which would sag the supply and make other running circuits malfunction
A powered-off block has large wiring and transistor capacitance, and a large current flows to charge it the instant power is connected. Turning on every switch at once can momentarily drop the supply network voltage sharply, risking malfunction in other blocks sharing it. So power-up follows a sequence, such as charging gradually through small switches before turning on the large ones.
- A. Correct. It limits supply noise.
- B. Contents do not multiply.
- C. It is unrelated to fabrication.