Is it alright if I connect the digital ground to the analog ground?

[XillixJeff]

Hi everyone,

If someone could help me out, it'd be greatly appreciated.

I'm just wondering if it's ok to connect the analog ground to the digital ground without blowing up my DAQ card. I MAY need to do this for a project, so I wanted to know if I had that option.

[Marni]

Hello Jeff. Thank you for contacting National Instruments. Nothing will happen if you connect the analog and digital grounds on your board. In fact, most of our boards already connect them in hardware. Have a great day!

Marni S.
National Instruments

[Fluxengr]

Jeff,
You're probably wondering why there are separate grounds if you can connect to both. Usually, Digital IO signal interaction isn't affected by EM. As long as the signal gets from point a to point b, in the digital world you're fine. But analog is a whole different beast which can be affect by EM or noise. Analog signals are influenced by what's going on around them. So usually you keep the analog portion of a PCB away from the Digital side. THE EM from the digital ground could affect the analog portion of a circuit. But NI is really good about protecting your signals so you're probably fine. If you get junk data, separate your grounds to make sure you're not picking up radiation from the digital side.
Hope this helps

[Buechsenschuetz]

As stated by others, usually the analog ground (AGND) is connected to the digital ground (DGND) somewhere on the board. The problem is the 'somewhere'. AGND and DGND have to be connected (if necessary) on a well-defined point to preserve analog signal integrity, and that's what designers of a DAQ board do.

If you connect DGND and AGND somewhere outside the board you will disturb their grounding technique, and maybe you will get unwanted noise and/or level shift on your analog signals. For precision or low signal measuring you should always keep both grounds separated and have them connected on the DAQ board only as it is done by the manufacturer.

[XillixJeff]

Thanks! You guys have been a great help. 🙂