Re : different ground planes in Multisim

[badrammour]

Hello everyone,

i would like to simulate in Multisim the following  circuit wich contains an optocoupler, and i would like to use a different ground for each side, my question is simple: is there any way to have different ground planes in Multisim & how can we realize this? Is there any other alternative?

[ChristopheS.]

Hi,

To do that you want, you need use a DGND.

The Ground (GND) symbol cannot be assigned to another net as the ground net 0 is considered to be universal for SPICE purposes. However, if there is a need for multiple ground nets, a DGND symbol can be used to do so.

Here is a link to a KB that explain how to add a DGND :

http://digital.ni.com/public.nsf/allkb/80119EBAA5471A8286257368003A39BB

Best regards

[badr ammour]

Thanks for your answer

In fact that's what i started doing, usind a DGNd,but i couldn't see the different planes (GNd separated from Dgnd) in Ultiboard.Do you have any idea about it?

I am also wondering  how many DGND  we can create in the same project, because i have many stages & i would like to separate them

Thanks again 

Badr

[ChristopheS.]

Yes you can have multiple DGND, you need just rename the RefDes with the required net name for each DGND.

For each DGND you will have a ground wire in Ultiboards after transferring the schematics.

Regards

[_user32]

badrammour,

I think this might be what you are looking for in Multisim:

http://forums.ni.com/t5/Circuit-Design-Suite-Multisim/Isolated-Ground-and-Analog-Ground-in-Multisim/...

For Ultiboard, you can create a special ground plane by:

     in v11, Place -> Copper Area (create the shape and then associate the right net to the area in the Net tab)

     in v12, Place -> Graphics -> Polygon (create the shape and then associate the right net to the area in the Net tab)

I'm not sure why we took the Copper Area off the menu completely (since Power Plane floods the plane, Copper Area is a polygon but now its buried deeper), Anyway ---  but the new polygon capability should get the job done.

Regards,

Pat Noonan

National Instruments

[badrammour]

thanks a lot _user32 for your help 

Just some points:

1.Is it obligatory to use a high impedance/resistor (in your case via the multimeter) to separate IGND & GND? i mean is it just a preventive measure because i think that they are separated when we use different RefDes?

2. I'm not sure, but i suppose you used AGND to show that the VDD  & Vcc sources are not referenced to the same ground, isn't it? By the way why did u use 2 resistors R1 & R2?

3.I didn't get why u used R7 (resistor with R=0 ohms, that's to say a wire) between 2 grounds that are supposed to be different.

4. I have thought about using different digital powers with values of 0V (as grounds)  before putting a post here, but my boss didn't like this idea & stillthinks it's not the appropriate method, that's why i am wondering if the method of Christophe S is not the appropriate one, with using different digital grounds with different RefDes, then different planes in ultiboard as you wrote it in your comment & finally associating every digital input to a different plane? What do u think about this approach? Don't you think it is sufficient to realize what i want to do?

Thanks  for both of u Christopher S & _user32 for your help

Regards 

Badr