cace 2.1.5

Circuit Automatic Characterization Engine

CACE

Circuit Automatic Characterization Engine

CACE is a set of python scripts that take an input file in the CACE 4.0 format and uses the information found there in combination with CACE-compatible testbenches and analysis scripts to characterize a circuit and to produce a datasheet showing the circuit performance.

Installation

You'll need the following:

• Python 3.8 or higher with PIP and Tkinter

CACE can be installed directly from PyPI:

$ python3 -m pip install --upgrade cace

Prerequisite design tools:

• xschem: https://github.com/stefanschippers/xschem
• ngspice: git://git.code.sf.net/p/ngspice/ngspice
• magic: https://github.com/RTimothyEdwards/magic

Usage

If installed as Python package, CACE can be started from the command line using:

$ cace

Or to start the GUI:

$ cace-gui

Information on how to use CACE can be found in the documentation at cace.readthedocs.io.

Development

Dependencies

[!IMPORTANT] You may need to set up a Python virtual environment.

To install the dependencies for CACE, run:

$ make dependencies

Python Package

To build the Python package, run:

$ make build

To install the package, run:

$ make install

To install the package in editable mode, run:

$ make editable

Documentation

To build the documentation, run:

$ make docs

To host the docs, run:

make host-docs

[!NOTE] The documentation can be viewed online at cace.readthedocs.io.

CACE GUI syntax

$ cace-gui [path/to/project.txt]

where optional file project.txt (normally <name_of_project>.txt
where <name_of_project> is the name of the circuit to be
characterized) is a circuit characterization description in the
file format described below.  If a file is not specified, then
the GUI window will come up without content.  Click on the button
with text "(no selection)" to find and select a characterization
file to load.  The project file may also be in JSON format.

Normally, cace_gui.py is called from a project top level directory,
while the project.txt file is usually in a subdirectory called
cace/.  The project.txt file may be the output file from a CACE
run, which will add results to all of the parameter entries.

There may be multiple characterization files in a single project
(repository), as a project may contain multiple subcircuits that
may need independent characterization or be able to be used as
standalone circuits, or a project may simply be a collection of
circuits (library) without a specific single top level. 

CACE command line syntax

$ cace <filename_in> <filename_out> [options]

where <filename_in> is a format 4.0 ASCII CACE file
and <filename_out> is the name of the file to write.

Options may be one of:

  -source=schematic|layout|rcx|all|best
  -param=<parameter_name>
  -force
  -json
  -keep
  -debug
  -sequential
  -summary

When run from the top level, this program parses the CACE
characterization file, runs simulations, and outputs a
modified file annotated with characterization results.

With option "-source", restrict characterization to the
specific netlist source, which is either schematic capture,
layout extracted, or full R-C parasitic extracted.  If not
specified, then characterization is run on the full R-C
parasitic extracted layout netlist if available, and the
schematic captured netlist if not (option "best").

Option "-param=<parameter_name>" runs simulations on only
the named electrical or physical parameter.

Option "-force" forces new regeneration of all netlists.

Option "-json" generates an output file in JSON format.

Option "-keep" retains files generated for characterization.

Option "-noplot" will not generate any graphs.

Option "-debug" generates additional diagnostic output.

Option "-sequential" runs simulations sequentially.

Option "-nosim" does not re-run simulations if the output file exists.
   (Warning---does not check if simulations are out of date).

Option "-summary" prints a summary of results at the end.

Examples

The following repositories contain example circuit designs, each having a "cace/" subdirectory with a specification input file in the format described below, and a set of testbench schematics which are used by CACE to measure all specified electrical and physical parameters, generate results, and analyze them to determine circuit performance over corners.

[!NOTE] Example repositories, like CACE itself, are currently a work in progress.

All repositories are rooted at: https://github.com/RTimothyEdwards/.

Example circuit repositories:

• sky130_ef_ip__instramp Instrumentation amplifier
• sky130_ef_ip__rdac3v_8bit 8-bit resistor ladder DAC
• sky130_ef_ip__samplehold sample-and-hold circuit
• sky130_ef_ip__driveramp Rail-to-rail driver amplifier
• sky130_ef_ip__ccomp3v Rail-to-rail continuous comparator
• sky130_ef_ip__rc_osc_500k R-C oscillator, 500kHz nominal output
• sky130_ef_ip__xtal_osc_16M Crystal oscillator, 4 to 15MHz
• sky130_ef_ip__xtal_osc_32k Crystal oscillator, 32kHz

Each of these repositories contains a circuit designed with the SkyWater sky130 process open PDK, and contains schematics, layout, and CACE characterization.

NOTE: These repositories are a work in progress, and may not exist yet or may not have a characterization setup for CACE.