Simulate Electronic Circuit using Python and Ngspice

Overview

What is PySpice ?

In short PySpice is an open source Python module which interface Python and the famous Spice circuit simulator.

Mainly it permits:

  • to define a circuit, so called netlist,
  • to perform a simulation using Ngspice,
  • to analyse the output using Numpy, Matplotlib, …

Is there some papers or talks about PySpice ?

You can look this talk Circuit Simulation using Python given at the PyParis 2017 conference (PDF file)

How to go further with PySpice ?

The best way to know what you can do with PySpice and to learn it, is to look at the examples.

How PySpice can be used for learning ?

  • PySpice comes with many examples covering several topics.
  • PySpice features a documentation generator which permits to generate an HTML or PDF documentation
cf. supra for the documentation generator features

How to install PySpice ?

The procedure to install PySpice is described in the Installation Manual.

How PySpice differs from simulator like LTspice ?

  • PySpice and Ngspice are Free Software and thus open source,
  • PySpice don’t feature a schematic editor (*) or GUI,
  • But it has the power of Python for data analysis,
  • And thus provide modern data analysis tools.
  • Moreover PySpice is feature unlocked due to its open design.

(*) However you can export netlist form Kicad to PySpice.

How can help a non GUI simulator ?

Obviously, it is not an evident task to write a netlist and a tool like a schematic editor help to visualise the circuit. It is more obvious that tool like Circuit_macros or Tikz are complex and need some practices. However the learning curve is not worst than for a music instrument.

Another question is to discuss the possibility to simulate a real design, i.e. to integrate the simulation in the EDA design process from the schematic to the PCB. In general, it does not make sense to simulate a real design, we will only simulate parts or models of a design to ensure the real design is right.

In fact each tool has advantages and drawbacks which are often orthogonal.

We have discussed the main drawback, we will now look at the advantages:

  • Since it is code, you can describe completely your simulation project. There is any actions that require to use a mouse to interact with the GUI.
  • And it can be easily versioned using a tool like Git.
  • If you work with an editor and a console in parallel, then you can easily and quickly change things and rerun the simulation, e.g. comment a diode or a capacitor to see what happen. Using a GUI, this task would require many actions.
  • Thanks to a tool like the documentation generator, you can enrich your simulation with text, formulae and figure all in one.

Finally, it is possible to use both approaches all together ? The technical answer is yes we can. For example the Modelica language uses a concept of annotations to describe the schema. A schematic editor like Kicad could be updated to interact closely with PySpice.

What is the benefits of PySpice over Ngspice ?

  • You can steer your netlist and simulation using Python.
Which supersede Spice parameters and expressions.
Which make Monte Carlo simulation easier for example.
  • You can analyse the output using the Python Scientific packages.
Which supersede tools like TclSpice.

How PySpice is interfaced to Ngspice ?

  • PySpice can parse a Spice netlist and generate the equivalent Python code or instanciate it.
  • PySpice can generate a Spice netlist.
  • PySpice can send a simulation and read back the output using either the server or shared mode.
By default, PySpice use the server mode. Shared mode is only required when you need advanced features.

When using shared mode

  • PySpice permits to define external voltage and current source in Python (or even in C).
  • PySpice permits to get and send data during the simulation process.
  • CFFI is used to interface C to Python.

How is defined netlist ?

  • Netlist is defined using an oriented object API,
  • But PySpice can also work with Spice netlist and import netlist from a schematic editor like Kicad.

How are handled Spice libraries ?

  • PySpice features a libraries manager that scan a path for library files.
  • Libraries can be included as is using the include directive.
  • Subcircuit can be defined as Python class.

How are handled units ?

  • PySpice features a unit module that support the International System of Units.
  • Unit value can be defined using function shortcuts or a special syntax: e.g. kilo(1.2), 1.2@u_kV, 1.2@u_mΩ.

Which version of Python is required ?

PySpice requires Python 3 and the version 3.5 is recommended so as to benefits of the new @ syntax for units.

Which version of Ngspice is required ?

You should use the last version of Ngspice and take care it was compiled according to the Ngspice manual, i.e. you should check somebody don’t enabled experimental features which could break PySpice, generate a wrong simulation, or produce bugs.

Notice that Ngspice is not distributed with PySpice !

Which flavour of Spice are supported ?

Up to now PySpice only support Ngspice. But PySpice could support easily any simulator providing an API similar to Ngspice shared.

What should you aware of ?

Users should be aware of these advertisements:

  • Ngspice and PySpice are provided without any warranty.
Thus you must use it with care for real design.
Best is to cross check the simulation using an industrial grade simulator.
  • Ngspice is not compliant with industrial quality assurance processes.
  • Simulation is a design tool and not a perfect description of the real world.

How is coded PySpice ?

PySpice is not the crappy code you can found on Github, but is rather coded carefully and use advanced Python features like metaclass.

What are the features of the documentation generator ?

The documentation generator features:

Somehow, it is similar to an Jupyter notebook, but it works differently and provides specific features.

What are the planned features ?

These features are planned in the future:

  • Improve the analyse experience.

Some other ideas are:

  • Implement a Modelica backend. Modelica is a very interesting solution for transient analysis.

The implementation of a simulator in Python is not planned since it would be too challenging to release a full featured and proved simulator. However you could look at the project Ahkab which aims to implement such Python based simulator. Notice any of the projects like Ngspice or Ahkab are compliant with industrial quality assurance processes.

News

V1.0.0

  • Bump version to v1.0.0 since it just works!
  • Fixed and completed Spice parser : tested on example’s libraries

V0.4.2

  • Fixed Spice parser for lower case device prefix.

V0.4.0

  • Git repository cleanup: filtered generated doc and useless files so as to shrink the repository size.
  • Improved documentation generator: Implemented format for RST content and Tikz figure.
  • Improved unit support: It implements now the International System of Units. And we can now use unit helper like u_mV or compute the value of 1.2@u_kΩ / 2@u_mA. The relevant documentation is on this page.
  • Added the Simulation instance to the Analysis class.
  • Refactored simulation parameters as classes.

V0.3.2

  • fixed CCCS and CCVS

V0.3.1

  • fixed ngspice shared

V0.3.0

  • Added an example to show how to use the NgSpice Shared Simulation Mode.
  • Completed the Spice netlist parser and added examples, we could now use a schematic editor to define the circuit. The program cir2py translates a circuit file to Python.

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