Decoupling and bypassing: Evaluate — “Power-supply decoupling uses a radio-frequency (RF) capacitor to shunt high-frequency noise and spikes to ground.”
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ACorrect
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BIncorrect
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COnly correct for linear regulators
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DCorrect but only above 100 MHz
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ECorrect only if using tantalum capacitors
Answer
Correct Answer: Correct
Explanation
Introduction / Context:Power-supply decoupling (bypass) is essential in digital systems to maintain stable logic levels and suppress switching noise. Small-value, low-ESL capacitors close to IC power pins provide a low-impedance path for high-frequency currents, thereby reducing voltage spikes on the supply rails.
Given Data / Assumptions:
- Digital ICs draw transient currents at clock edges.
- Bypass capacitors present low impedance at high frequency.
- Placement close to IC power pins minimizes loop inductance.
Concept / Approach:A ceramic RF bypass (e.g., 0.1 µF) from Vcc to ground shunts fast transients locally, maintaining a clean local supply. Larger bulk capacitors stabilize lower-frequency sag. Together they form a multi-decade impedance control strategy.
Step-by-Step Solution:
Identify high di/dt current pulses from logic switching.Provide a nearby low-impedance reservoir using small ceramic capacitors.Ensure short traces to reduce inductance so HF spikes are effectively shunted.Verification / Alternative check:Scope measurements show reduced supply ripple/spikes when decoupling is properly applied at each IC compared to an undeco upled board.
Why Other Options Are Wrong:
- Incorrect / linear-only / >100 MHz-only / tantalum-only: Bypass principles are universal. Value and dielectric type are design choices; ceramics handle HF well, tantalum handles bulk energy but is not mandatory for HF shunting.
Common Pitfalls:Placing capacitors far from pins; using only bulk capacitance; ignoring ground return path and plane quality; overlooking ESR/ESL effects at target frequencies.
Final Answer:Correct