Why there must be low impedance path between power & gro

[cj9404]

A Basic question

In High speed PCB design, there is a design rule regarding power sistribution, it says there must be a low impedance path between power and ground.


Can anybody tell what is the purpose for that?

Thanks alot.

 

[btbass]

A Basic question

This is acheived by distributed decoupling. The aim is to acheive a power supply with a low common-path noise and to distribute power everywhere at a uniform stable voltage.

 

[Rame]

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

 

[electron_boy]

Re: A Basic question

**broken link removed**

 

[vijaya_narayana]

Re: A Basic question

Can anybody clear me about the low impedance path because the decoupling is used to reduce transients and the noise gnerated in the poer trace but the low impedance path beween the ground and power i dont understand can any body explain me this

 

[hamdard]

Re: A Basic question

The low impedance path gives least resistance to current to flow for completing the loop (of course with ground).

 

[vijaya_narayana]

Re: A Basic question

so the capacitor in between the power and ground is used as a least resistance path due current component in the power track am i correct

 

[jayasuryan]

Re: A Basic question

If the grounds are connected with a high-impedance path, then there is a voltage drop between the ground pins.This causes disruptions to all of the devices referenced to this ground and can degrade input noise margins.