Is a decoupling capacitor required for the power supply?

The spike current that is generated at switching fluctuates potentials of V_CC and GND and may cause overshoot or undershoot of the output waveforms or delayed speed. Therefore, it is necessary to keep the impedance of the power source line against high frequency at lower level.

Specifically,V_CC and GND wires should be thick and short, and it is ideal that a decoupling capacitor (0.01µF to 0.1µF) is inserted as a high-frequency filter for each IC.

For low-frequency filters, a 10µ:F to 100µF capacitor is generally used for each board.

[Figure: Example of decoupling capacitors inserted between V_CC-GND]