Parasitic Models in H35

 

The parasitic models for the NMOSI20H, NMOSI50T/M/H(S), PMOS20H and PMOS50T/M/H(S) have parasitic PNP transistors included. In order to measure the current through this parasitic transistor the substrate node had to be made accessible. This was made by adding the psub node as inherited connection. The advantage of the method is that no additional pin had to be added to the device and therefore old schematic don't have to be changed.

Other device, like the floating LV transistors and the HV PMOS transistor have parasitic diodes which also have been made accessible.

How to make the parasitic current accessible

  • Place the device as usual
  • Select the device and Edit the Object Properties <q>
  • Select Add Property in the Edit Object Properties form
  • Add a netSet type property with the name psub and as value add the net name of the local psub node.
    The local psub node has to be a global definition (ending with "!") and can be freely chosen.


    Adding Properties

    In the example psub_M2! will be the local psub node.
    Use the option Display = both to display the netSet property in the schematic:


    Editing the Object Properties

    In the schematic you will now have the substrate definition displayed near the device:


    Displaying the net name in the schematic

  • The local Substrate node has to be defined:
    Add a 0V Voltage Source to the ground node and add the local psub node name to the wire.


    Adding the Ground node to the schematic

  • The current through the parasitic bipolar can now be probed on the nodes of the addition Voltage Source.

  • The netSet property can also be added to hierarchical blocks. The substrate net is then propagated down the hierarchy and every instance in the hierarchy is connected to the specified substrate net. A netSet property on a instance will override the hierarchical netSet property.

What to take care of:

  • Don't descend into the schematic of the primitive devices and probe the currents there.
    The subcircuit still uses models with inline subcircuits. The current through the parasitic elements are not displayed on inline subcircuit model. Always probe on the symbol of the device.
  • Add the probes to the Outputs To Be Plotted before starting the simulation.
  • Or - when using Save All ... select Select Device Currents = "all" and set Set subcircuit probe level to n+1. Where n is the level in the hierarchy of your schematic. If your schematic is flat, than means only instances of the PRIMLIB place in the schematic, set subcktprobelvl = 1.
     
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