'M' element must have four nodes in NetlistSpiceReaderDelegate::parse_element

Comments

• dick_freebird

  June 12

  Are you sure that a different element
  (like JFET) wouldn't do?

  Or something like BSIMSOI rigged for
  fully depleted "bodyless" MOSFET?

  Check out what the CMOS RF switch
  people do.
• Matthias

  June 12

  Sigh ... Spice is a mess

  "parse_element" is based on the Spice comprehension of ngspice, which requires four terminals for "M" and there are many weird variants - I guess something like M d g s b model=nfet was causing an issue here. But I'd have to dig in the files to find the reason for this change.

  But you can basically reimplement "parse_element" in the SpiceReaderDelegate too. Note that there is a "parse_element_components" function available to simplify the task and you only want to change the way how "M" is parsed. So you could add some code like this to the reader delegate:

    def parse_element(s, element)
       if element != "M"
         super
       else
         data = parse_element_components(s)
         data_out = RBA::ParseElementData::new
         data_out.parameters = data.parameters
         data_out.model_name = data.strings[-1]
         data_out.net_names = data.strings[0..-2]
         return data_out
       end
     end
  

  (Disclaimer: not tested).

  This removes the restriction imposed by the default implementation.

  Matthias
• dick_freebird

  June 12

  I think ideally the "recognition" and "extraction"
  should be so "meta" that an arbitrary bundle of
  polygons can map to an arbitrary device which
  has bound to it an arbitrary netlisting format
  template (name, nodes, model, properties).

  Then this all falls to the user's "technology"
  definitions?

  On the schematic side this is pretty usual.

  I don't understand anything about the layout
  side.
• Daaan

  June 16

  Thanks Matthias and everyone.

  I've got it working. The code as you listed worked fine for parse_element. For element() I had to change the logic from if el != "M" || nets.size != 4, but I think that's just a typo in the original.

  The lines are of the kind M2 NET1 NET2 NET3 TFT l=8u w=20u - I think this is Silvaco, so hspice?! Agreed that SPICE is a mess!

  It took me a while to work out how to write the computed layers in a way that satisfies the "gate must be rectangular, sd must not overlap gate", etc. requirements, but I got there in the end and it's now working beautifully - it highlighted a couple of issues which would have been catastrophic! and a couple of lesser issues, but which are still nice to resolve.

  In case it's useful to others, I've left the code below.

  class MOS4To3ConvertingSpiceReader < RBA::NetlistSpiceReaderDelegate
  
    def parse_element(s, element)
       if element != "M"
         super
       else
         data = parse_element_components(s)
         data_out = RBA::ParseElementData::new
         data_out.parameters = data.parameters
         data_out.model_name = data.strings[-1]
         data_out.net_names = data.strings[0..-2]
         return data_out
       end
     end
  
    def element(circuit, el, name, model, value, nets, params)
      if el != "M" || nets.size == 4
        # all other elements are left to the standard implementation
        return super
      end
      # provide a device class
      cls = circuit.netlist.device_class_by_name(model)
      if ! cls
        cls = RBA::DeviceClassMOS3Transistor::new
        cls.name = model
        circuit.netlist.add(cls)
      end
      # create a device
      device = circuit.create_device(cls, name)
      # and configure the device
      [ "S", "G", "D" ].each_with_index do |t,index|
        device.connect_terminal(t, nets[index])
      end
      # parameters in the model are given in micrometer units, so 
      # we need to translate the parameter values from SI to um values:
      device.set_parameter("W", (params["W"] || 0.0) * 1e6)
      device.set_parameter("L", (params["L"] || 0.0) * 1e6)
      # TODO: if required, add AS,AD,PS and PD ...
      return true
    end
  
  end
  

  and then during the read, I have

  # Instantiate a reader using the new delegate
  reader = RBA::NetlistSpiceReader::new(MOS4To3ConvertingSpiceReader::new)
  
  # Import the schematic with this reader
  schematic("test_circuit.net", reader)