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Display Your Know How: Decoupling Capacitor

PCBTech

The golden rule of decoupling capacitor placement is to minimize the distance between the IC’s voltage pin and the capacitor.

What about the routing of the capacitor to POWER and GROUND pins/planes!!

Which among the above decoupling capacitor routing configurations is better?

Any improvements that can be done?

Simply answer by letter or include any reason to support your answer. Alternatives and opinions are welcome!

Parents

  • In the early years senior hardware engineers were advising me to place capacitors directly at the signal receiver pin tied to ground. This was explained to be "filtering out" high frequency noise from the signal. So the cap was acting as a short to ground for higher frequencies.  

    But later on, SI experts were advising that capacitors act as a source of voltage when there is a supply drop due to high frequency demands. The capacitors then temporarily supply voltage for quick short bursts. So which is it, a short for filtering or a voltage supply?   

Reply

  • In the early years senior hardware engineers were advising me to place capacitors directly at the signal receiver pin tied to ground. This was explained to be "filtering out" high frequency noise from the signal. So the cap was acting as a short to ground for higher frequencies.  

    But later on, SI experts were advising that capacitors act as a source of voltage when there is a supply drop due to high frequency demands. The capacitors then temporarily supply voltage for quick short bursts. So which is it, a short for filtering or a voltage supply?   

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