shorting of analog and digital grounds

Shorting grounds? You mean where to connect the grounds?

This depends on your current paths. Normally I would expect grounds to be connected at the power supply. Just connected, no diode, normally no inductor too. The inductor is sometimes used to prevent emc into the analog parts. But you have to be careful as it may even make things worse. The analog and digital part are like 2 independend systems, the are connected at the ground.

It ususally is important that digital currents do not flow through the analog ground (and the other way around). That current would lead to fluctuations of the ground, and when you do not have a balanced system you use the ground as reference.

Take care at the point where you do the AD conversion. Use a convertor with balanced inputs and connect the '-' input to the analog ground, NOT the digital ground. When the convertor has only one input and uses the GND itself as 0-reference, then this will be the point where the 2 grounds connect. Make sure nu digital currents flow through it.

It is not possible to give better info without seeing the schematics or setup first. Or without knowing what you want to do: preventing disturbances caused by digital currents into the analog part, or preventing spikes etc coming from cables from the analog part into the digital part.

Regards, Pieter Hoeben

thanks for info .i can give u some brief idea abt my design i am having and adc working at 65Mhz the sampled data is going to FPGA(vertix2) .

Hi Anshu,

Maybe this web contains what you are looking for:

Regards,

Quitus.

thanks for the link regards anshu