Is a decoupling capacitor required for the supply of a general purpose logic IC?
A decoupling capacitor is recommended for stable circuit operation. The reason is that if AC components such as noise are superimposed on the power supply voltage supplied to the general purpose logic IC, it may cause voltage fluctuations and destabilize circuit operation.
By connecting the decoupling capacitor as close to the IC pin as possible, a stable power supply voltage with little noise can be supplied to the IC. The spiking current generated during switching causes the potential of VCC, GND to fluctuate, causing ringing of the output-waveform and speed delay. Therefore, the impedance of the power supply line against high frequency should be kept low.
Specifically, VCC and GND lines should be thick and short, and it is ideal to insert a decoupling capacitor (0.01 µF to 0.1 µF) close to the power pin of each IC, which acts as a high-frequency filter. Place the decoupling capacitor as close to each IC as possible. The distant placement not only reduces the effect, but may also radiate the switching noise of the IC.
For low-frequency filtering, a 10-µF to 100-µF capacitor is generally used for each board.
(Fig. 1)
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