Re: A Basic question
Hi,
In addition to btblass statement on above subject,it is to Reduce board noise and improving immunity to electromagnetic interference (EMI).
The VCC-to-ground decoupling should be evenly distributed to reduce the loop area for noise generated in the VCC lines.
VCC-to-ground decoupling is important because the VCC traces can carry common-mode switching transient noise current. The magnitude of the radiated field from this current is directly proportional to the magnitude of the current, I, and the loop area traversed by the current, A. Evenly distributing decoupling capacitance around the layout helps reduce the loop area of the higher- frequency components of the switching transient currents.
Hope this helps you...
Regards,
Ramesh