problem with analog ground(AGND)

[vivek20055]

Hi,

I am designing a 4 layer pcb board. For the GND layer I have given seperate GND ground for high current path(from transistors) which is connected to normal GND at a point.

I have given the seperate analog ground(AGND).

My professor commented like this:

What is this separation for the ground used for?

Looks strange to me. The upper part will be more fluctuating.

If you only have analog parts over the analog GND then it is good that you are using a separate analog gnd but I am surprised that the analog part is so spread. A problem might be that your analog GND is connected at the end of the digital GND and digital noise will be added to your analog gnd. A start connection to the common GND separation might improve.


what does this mean?????

How can I add start connection???

I am adding image with this message

Regards
Vivek Alaparthi

 

[pwdixon]

He could have actually been saying a STAR connection was required. Usually the star point is at the power supply.

 

[vivek20055]

Hi,

Thanks for ur reply

what is star connection?
what is the need of star connection at power supply?
How is star connection helpful at power supply???


Regards,
Vivek Alaparthi

 

[marce]

Start by putting this search into google:
mixed signal grounding
then read as many of the documants that come up, here is one by the master of these things:
http://www.hottconsultants.com/pdf_files/june2001pcd_mixedsignal.pdf