Techfile Files

Techfiles are typically found in circuitbrew/tech/process. Each process node should be a subdirectory here, with two files like the following for Skywater:

    circuitbrew/
        tech/
            process/
                sw130/
                    sw130.sp
                    tech.yml

The sw130.sp file is the main SPICE template that's written using Mako. The process parameters are specified in tech.yml:

tech: sw130
voltage: 1.8
temp: 85
output_dir: 'output'
template: 'sw130.sp'

Fet:
  auto:
    l: 0.5    # Length
    w:  1.0   # Default width
    vt: lvt   # Default vt 
    width_id: w  # Name in spice xtor model for width/nfin/etc
  Pfet:
    auto:
      # Define xtor models for different VTs
      lvt: sky130_fd_pr__pfet_01v8_lvt
  Nfet:
    auto:
      # Define xtor models for different VTs
      lvt: sky130_fd_pr__nfet_01v8_lvt

This tech file is loaded at start up and stored in every Module instance as a dict: self.sim_setup. In addition, everything is accessible inside your SPICE template file, so if you wanted to add a configuration setting/value pair into your SPICE file, you could just add it to the top-level of the tech.yml file. Then, write it into your sw130.sp file with Jinja syntax (e.g. ${new_option})

The keys that are named after Module names are meant to provide a way to get configuration settings to specific classes. Anything that is under the auto key is automatically set as a member attributes for the matching class's objects. For example, every Fet module object automatically has the l, w, vt, and width_id member attributes set. These can also be overridden via keyword args to the constructor.

So, doing the following will create a Fet with width 2.0 while keeping the length as 0.5:

    ...
    self.mynfet = Nfet(w=3)

Make sure you follow the class hierarchy in the tech.yaml file if you want the attributes to apply properly.