Language plugin for Qucs (see for an implementation)

The basic idea is to parse a qucs schematic or a qucsator netlist.


qucsator is the default simulation engine behind the qucs user interface. it does dc/ac/tran and sparam analysis, and maybe a (simplified, linear?) kind of harmonic balance.

The use is quite limited due to the interface between qucs and qucsator, but it defines a sort of interface between the projects.

gnucsator aims to be a drop-in replacement for qucsator, that means it will * provide the components implemented in qucsator, * have to read the netlist (unless/until somebody fixes this) * interpret simulation commands (embedded into the netlist) like qucsator. * produce output equivalent to qucsator output (“dat” file format).

Example of a qucsator netlist file
# Qucs 0.0.16  bridge.sch
IProbe:Pr1 _net0 _net1
R:R2 _net2 _net3 R="500 Ohm" Temp="26.85" Tc1="0.0" Tc2="0.0" Tnom="26.85"
Vdc:V1 _net3 gnd U="1 V"
R:R5 gnd _net2 R="Rmeasure" Temp="26.85" Tc1="0.0" Tc2="0.0" Tnom="26.85"
R:R1 _net0 _net3 R="Rbranch" Temp="26.85" Tc1="0.0" Tc2="0.0" Tnom="26.85"
R:R4 gnd _net0 R="Rbranch" Temp="26.85" Tc1="0.0" Tc2="0.0" Tnom="26.85"
.DC:DC1 Temp="26.85" reltol="0.001" abstol="1 pA" vntol="1 uV" saveOPs="no" MaxIter="150" saveAll="no" convHelper="none" Solver="CroutLU"
R:R3 _net1 _net2 R="500 Ohm" Temp="26.85" Tc1="0.0" Tc2="0.0" Tnom="26.85"
.SW:SW1 Sim="DC1" Type="lin" Param="Rmeasure" Start="10 Ohm" Stop="1 kOhm" Points="100"
.SW:SW2 Sim="SW1" Type="lin" Param="Rbranch" Start="200 Ohm" Stop="1 kOhm" Points="4"
Eqn:Eqn1 Umeasure="500 * abs(Pr1.I)" Export="yes"
Description of the Netlist file

First line shows the version of the qucs and the file path

_net gives information about in between which nodes the component is connected

The list of the components in Qucs can be seen in the link below

Description of the qucsator output file

TODO. tl;dr; some upside-down xml inspired layout without simulation labels.

description of the simulation commands


Description of a schematic file

The schematic format used in qucs is not currently used for simulation purposes. Qucs compiles an intermediate self-contained circuit representation (“netlist”) including simulation commands before invoking qucsator. Hence the format used for the schematics (some XML-like format) is not relevant yet. It will be easy to represent the schematic as a standardized (e.g. verilog) netlist, once Qucs supports additional file formats. This will make the schematic files more useful and the intermediate netlists obsolete.

Implementing the Components

Qucs essentially provides a hardcoded set of components plus variants (paramsets) through a “component library”. We need to provide (most/all) of the components supported by qucsator. It would be possible to wrap them, on an implementation/binary level using a wrapper similar to spice_wrapper (e.g. This involves some effort and workarounds with no clear benefit. In particular, there are only few components, this could be used for.

The approach here aims at implementing the components in terms of modules that (re-)use some functionality of existing gnucap components. Some components can be directly wrapped through a subcircuit declaration or paramset. Others can be easily represented by subcircuits containing few components (a.k.a. macros). Ideally all components would be implemented in verilog-A. At the current stage it would make more sense to support user provided Verilog-A models in qucs. Some work has been done in that direction, but qucsator will not support Verilog-A input in the foreseeable future.

gnucap/user/language_plugin_for_qucs.txt · Last modified: 2018/07/07 17:36 by felixs
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