NI Home > Community > NI Discussion Forums

Circuit Design Suite

Showing results for 
Search instead for 
Do you mean 
Reply
Active Participant
_user32
Posts: 373
0 Kudos
Accepted Solution

Isolated Ground and Analog Ground in Multisim

What is the availability of isolated or analog grounds in Multisim?  Multisim allows for 2 primary types of grounds, standard  ground (can also be called earth ground, represented always as net '0') and digital ground, however sometimes in a design you will need multiple ground references for the various areas of the design including an earth or chassis ground point, digital ground and analog ground and sometimes an isolated ground. 

 

How can this be accomodated in Multisim from both a modeling and layout standpoint?

 

Regards,

Patrick Noonan
Business Development Manager
National Instruments - Electronics Workbench Group
50 Market St 1-A
South Portland, ME 04106
Phone: 207 892-9130
Email: patrick.noonan@ni.com 

Active Participant
_user32
Posts: 373
0 Kudos

Re: Isolated Ground and Analog Ground in Multisim

[ Edited ]

For isolated ground - from a modeling standpoint - one method involves creating a netname (such as isognd) and creating a physically isolated connection from standard ground (net 0) with a large resistor value (or other appropriate high impedance network).   From a layout standpoint however, managing a single netname can be cumbersome and error prone.

 

Attached is an alternative approach using specially created symbols (IGND, V_ISO, AGND and CGND) providing for an isolated ground, isolated DC voltage source (referenced to IGND) and an Analog Ground, respectively.   These similar to  a previous post created, allowing for multiple VCC or VDD connections in a design.

 

NOTE: When IGND and AGND are initally placed, they will be set at '5V', you will need to manully change the value to 0V to make them properly function.  Here are the components and notes on each.

 

IGND   : Isolated ground with a built-in 10M Ohm resistor to standard ground (this can be changed in the SPICE model if needed from the DB Mgrr)

V_ISO : Isolated DC source referenced to IGND.  IGND must be present in the isolated circuit for functioning properly

AGND  : Analog ground with a small built-in 0.001 Ohm resistor to standard ground (this can be changed in the SPICE model if needed from the DB Mgr)

CGND : Chassis ground with a small built-in 0.001 Ohm resistor to standard ground (this can be changed in the SPICE model if needed from the DB Mgr)

 

Typically AGND, DGND, CGND and standard GND (net 0) would be tied together in layout with a star ground connection.  This can be done in Ultiboard by using a net bridge connection.

 

Regards,

Patrick Noonan
Business Development Manager
National Instruments - Electronics Workbench Group
50 Market St 1-A
South Portland, ME 04106
Phone: 207 892-9130
Email: patrick.noonan@ni.com 

 

Message Edited by _user32 on 09-08-2009 04:22 PM
Active Participant
_user32
Posts: 373
0 Kudos

Re: Isolated Ground and Analog Ground in Multisim

Here are the examples:

 

Alternative Grounds Example.ms10 - Multisim example showing IGND, AGND, CGND and V_ISO and how to properly connect and measure

Isolated Source and Ground Example.ms10 - Another example showing IGND and V_ISO measured relative to earth ground (net 0)

Special_Gnds.prz - database update file - creates new family "Special_GNDs" (Multisim 10.1)

 

Thanks to the original user who requested these.

 

Regards,

Patrick Noonan
Business Development Manager
National Instruments - Electronics Workbench Group
50 Market St 1-A
South Portland, ME 04106
Phone: 207 892-9130
Email: patrick.noonan@ni.com 

Active Participant
_user32
Posts: 373
0 Kudos

Re: Isolated Ground and Analog Ground in Multisim

Specialty Ground symbols for Multisim v10, v11 and v12.

 

Includes

AGND (analog ground)

CGND (chassis ground)

IGND (isolated ground)

V_ISO (voltage source, referenced to IGND)

 

- PatN