Decoupling capacitors: In digital electronics PCB design, should each IC's decoupling capacitor be connected between that same device's VCC (power pin) and its own local ground near the pins, or should it be tied from the VCC of one device to the ground of a different device?

Introduction / Context:Decoupling (bypass) capacitors are critical in digital electronics to provide a low-impedance local energy reservoir and to control high-frequency noise near an integrated circuit. This question checks correct placement of decoupling capacitors relative to each device's power and ground pins.

Given Data / Assumptions:

• ICs draw fast transient currents when internal gates switch.
• Power distribution networks have nonzero inductance and resistance.
• A small ceramic capacitor (for example, 0.1 µF) is typically used per IC.

Concept / Approach:For effective high-frequency decoupling, the loop area formed by the capacitor, the IC's VCC pin, and the IC's ground return must be minimized. The capacitor must be placed physically close to the same device's pins so that current flows in a very short loop, reducing inductive impedance and voltage droop (delta V = L * di/dt).

Step-by-Step Solution:

Verification / Alternative check:Examine supply ringing on an oscilloscope: with proper local decoupling, high-frequency droop and ground bounce reduce markedly compared to cross-device connections.

Why Other Options Are Wrong:

• True: Incorrect—cross-connecting decouplers increases loop area and noise.
• Only on multilayer boards: Layer count does not justify cross-device decoupling.
• Only if star ground is far: Star points are system-level; local HF loops still must be minimized.
• Depends on capacitor value: Placement and loop inductance dominate HF behavior more than value alone.

Common Pitfalls:Placing capacitors far from pins, sharing one capacitor across several ICs, and routing long serpentine traces to the capacitor reduce effectiveness.

Final Answer:False — the decoupling capacitor should be local to the same IC, between its VCC and its ground.