Bringing PCB-Design and Simulation Together with eSim

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Efficient electronic design automation (EDA) calls for performing design layout, simulation and analysis using a single tool. The open source community delivers a software for the purpose in the form of eSim. Developed by a team from IIT Bombay, eSim packs a host of features and modules that make EDA comprehensive and simple. It is built using Python and merges KiCad circuit design software and Ngspice layout simulation package, which makes it a handy tool to develop and analyse new layouts and sub-circuits, or edit existing ones.

The latest version of eSim software has a gamut of modules that work in sync to provide a compact circuit layout framework and a simulation space-all under one roof. Let’s explore these different modules and how they make EDA easy.

Circuit design

Circuit design starts with schematic creation and netlist generation, followed by creating the component footprint and then finalising the circuit layout. KiCad tools like EEschema, CvPCB and PCBnew are meshed with eSim to enable circuit design.

eSim Startup page (Image source: esim.fossee.in)
Fig. 1: eSim Startup page (Image source: esim.fossee.in)

Schematic creation with EEschema

EEschema is a popular tool for circuit schematic creation and editing. It allows you to draw the circuit and controls, which are passed down for creation of component footprints. EEschema manages the components library for eSim, enabling users to view, create or edit components. The netlist of the circuit is also developed here. It is the list of components and nodes that will be available in a circuit.

Component footprinting with CvPCB

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CvPCB completes component layout on the PCB schematic. First, it helps in assigning the correct component footprints to the schematic and netlist generated by EEschema. Then it enables the user to place components on the schematic based on the footprints. Options like footprint filtering and list viewing, and 3D view of components help to avoid errors in the process. CvPCB has the capability to assign footprints automatically with equivalence tables, thus ensuring quick and accurate footprint association.

Layout formation with PCBnew

PCBnew works with EEschema and CvPCB to create PCB layout. Inputs are the schematic and netlist created by EEschema and PCB component layouts based on the footprint created by CvPCB. PCBnew has a plethora of features that help in creating an error-free PCB design. One such major feature is the design rules check (DRC), which points out any erroneous arrangement in the circuit in real time. The visual interface is a rat’s nest display, where components and nodes are connected by a hairline. Any movement made to the components moves the circuit along. Modifications made to the circuit schematic or components are automatically integrated by PCBnew. Effective auto-routers help in circuit production with export/import capability in SPECTRA dsn format. PCBnew also supports ultra-high-frequency circuit design.

Model framing

The eSim team has created two modules that can help users to create complex circuit models and hierarchies: Model Builder and Subcircuit Builder.

Model Builder

With the help of Model Builder, users can define the circuit model they want to build in eSim. Existing models can be edited as well. Circuit model options in Model Builder include diode, bipolar junction transistor (BJT), junction field-effect transistor (JFET), metal-oxide semiconductor field-effect transistor (MOSFET), magnetic core and IGBT.

Subcircuit Builder

Its main function is to create the sub-circuit for a component. The sub-circuit so created can be used in other circuits as well. Subcircuit Builder module has a feature to define new components like op-amps and IC 555. Users can also edit existing sub-circuits with this module.

Simulation

Built circuit layouts need to be verified for their validity, integrity and efficiency. Simulation software serves this purpose. eSim software includes a group of simulation tools to convert and visualise the circuit layout created using KiCad packages and Model Builder.

KiCad to Ngspice converter

The netlist generated by schematic editors needs to be converted into an Ngspice-compatible format. Developed in-house by the eSim team, the KiCad-to-Ngspice converter module helps to achieve that along with analysis parameters and source details. You can also add or edit device models and subcircuits present in the circuit schematic.

Simulation with Ngspice and NGHDL

Ngspice is a popular circuit simulator tool integrated into eSim platform. It can analyse non-linear DC, non-linear transient and linear AC lines. It supports almost all essential components including inductors, resistors, capacitors, individual current and voltage sources, transmission lines (both lossless as well as lossy), switches and distributed resistor-capacitor lines. It also supports all types of models provided by Model Builder. After the schematic and model are selected and converted, Ngspice displays the analysis in a graphical user interface.

NGHDL is an add-on simulation suite that eSim uses for mixed-mode circuit simulation using simulation tool GHDL.

Fig. 2: Simulation on eSim (Image source: esim.fossee.in)
Fig. 2: Simulation on eSim (Image source: esim.fossee.in)

OpenModelica

This is a modeling and simulation tool with two modules: OMEdit, an integrated development environment (IDE) for the modeling and simulation logic, and OMOptim, another IDE for optimising the simulation. It incorporates Modelica programming language.

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