Re decoupling capacitors

[Anand Ranjith Mark]

Hi all,
In high speed PCB design how to choose decoupling capacitor value? is any formula is there for calculate it?
how they choose Low value capacitors are used for high frequency and high value capacitors are used for low frequency ..?
mostly all are using for decoupling capacitor values like 0.1uF and 0.01uF.how they select ??
and the number of capacitors will depends on which one?

 

[ud23]

https://www.intersil.com/content/dam/Intersil/documents/an13/an1325.pdf

 

[marce]

Size Matters......
The smaller the package the better, but also routing and via placement will have a big effect on how the cap performs, the aim is to minimise parasitic inductance.....

 

[jiripolivka]

The highest decoupling capacitance value is determined by the lowest frequency a powered device uses. Adding smaller parallel capacitors extends the bandwidth. What you want is that your system is not affected by a higher DC power supply impedance- it should be close to zero.