Why we need to put decoupling capacitors used for power rails close to the IC pins?
The caps as close to the power and ground pins as possible. This is one entence always said by professional persons here. Why do they have to be soldered very near to the pins? And I expressed as decoupling capacitors. Is decoupling and bypass caps same thing?
A short circuit for these RF signals is formed by the decoupling caps so the closer you mount the decoupling caps to the power pins of the ICs the smaller the loop will be.
If you put the capcitor farther, the trace length and the parasictic inductance will be more. So, it is advised to place it as close to the voltage or ground pin as possible.
The decoupling and bypass capacitors are the same thing. The power supply to a chip would have a zero impedance at all frequencies. If the power supply has a finite impedance it will act as an unwanted coupling path. If the impedance i shogher, this unwanted coupling path will be stronger.
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