Analog Filter Design Toolbox

Advanced Instrumentation I — Class Lab Project
Universidad Iberoamericana · Campus Ciudad de México · 2026

A PyQt6 desktop application for the design, synthesis, and SPICE simulation of analog active filters. The GUI scaffold and all callbacks are provided; students implement the signal-processing and circuit-synthesis back-end.

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Features

Area	Detail
Approximations	Butterworth · Chebyshev I · Chebyshev II · Elliptic (Cauer)
Filter types	Low-pass · High-pass · Band-pass · Band-stop (Notch)
Topologies	Sallen-Key · Tow-Thomas (UAF42) · Deliyannis-Friend
Component rounding	E6 / E12 / E24 / E48 / E96 / Exact
Plots	Magnitude · Phase · Group Delay · Pole-Zero Map · Schematic
Simulation	PySpice / ngspice AC analysis with IC model selection
Theme	Light and Dark mode, toggled at runtime
i18n	English / Español (easily extensible)

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Project layout

filter-toolbox/
├── main.py                  # Entry point
├── mainwindow.py            # GUI controller  ← do NOT modify
├── mainwindow.ui            # Qt Designer layout
├── about_dialog.ui          # About box (edit names here)
├── filter_design.py         # ★ STUDENT CODE ★
├── requirements.txt
├── CONTRIBUTING.md
├── LICENSE
└── resources/
    ├── __init__.py
    ├── i18n.py              # All UI strings (EN + ES)
    └── styles.py            # Light / Dark QSS themes

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Quick start

# 1. Clone
git clone https://github.com/<org>/filter-toolbox.git
cd filter-toolbox

# 2. Create virtual environment
python -m venv .venv
source .venv/bin/activate        # Windows: .venv\Scripts\activate

# 3. Install Python dependencies
pip install -r requirements.txt

# 4. Install ngspice  (required for SPICE simulation)
#    Ubuntu/Debian : sudo apt install ngspice
#    macOS         : brew install ngspice
#    Windows       : https://ngspice.sourceforge.io/download.html

# 5. Launch
python main.py

Python 3.10 or newer is required.

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Student entry points

All student work goes in filter_design.py. Each function has a full docstring with the expected signature, return type, and implementation hints.

#	Function	Description
1	compute_minimum_order(spec)	Minimum filter order from the spec
2	compute_transfer_function(spec)	Full H(s) + computed order
3	factored_biquads(tf)	Cascade of 1st / 2nd-order sections
4	compute_frequency_response(tf, …)	Magnitude, phase, group delay
5	synthesise_sallen_key(…)	R/C values for Sallen-Key topology
6	synthesise_tow_thomas(…)	R/C values for Tow-Thomas / UAF42
7	synthesise_deliyannis(…)	R/C values for Deliyannis-Friend
8	generate_spice_netlist(…)	SPICE netlist string
9	run_spice_simulation(netlist)	PySpice AC simulation

Helper utilities already implemented (do not modify):

• round_to_eseries(value, series) — snap to nearest E-series value
• eseries_error_pct(ideal, rounded) — percentage rounding error
• FilterSpec.ripple_eps — ε derived from Ap automatically
• FilterSpec.omega_p/s/p2/s2 — rad/s conversion from Hz fields

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Editing names in the About box

Open about_dialog.ui in Qt Designer and edit the label text directly — no Python changes needed.

Widget	Content
lblInstructor1/2/3	Instructor names
lblStudent1/2/3	Student names and roles
lblCourse	Course name
lblInstitution	Institution
lblYear	Academic year

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Editing the GUI

Open mainwindow.ui in Qt Designer. The following widget names must not be changed (they are referenced by mainwindow.py):

cbApproximation · cbFilterType · sbFp · sbFs · sbFp2 · sbFs2 sbAp · sbAs · cbImplementation · cbIcModel cbRSeries · cbCSeries · sbRBase · sbCBase btnDesign · btnSimulate · btnExportNetlist · btnExportReport · btnToggleTheme tabPlots · wgtMagnitudePlot · wgtPhasePlot · wgtGroupDelayPlot · wgtPoleZeroPlot tblComponents · lblStatus · lblTitle · lblSchematic lblComputedOrder · lblFp · lblFs · lblFp2 · lblFs2 lblAp · lblAs · lblOrderLabel · lblImpl · lblIcModel lblRSeries · lblCSeries · lblRBase · lblCBase · leftPanel

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Adding a language

1. Open resources/i18n.py
2. Copy the "es" block and give it a new key (e.g. "fr")
3. Translate all values
4. Add "Français": "fr" to the LANGUAGES dict at the top

The new language appears automatically in View → Language.

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Adding a SPICE op-amp model

Place the .lib subcircuit file in resources/spice_models/ and reference it in generate_spice_netlist() with a .lib directive.

Free model sources:

• TI — https://www.ti.com/design-resources/design-tools-simulation/spice-models.html
• Analog Devices — https://www.analog.com/en/design-center/simulation-models/spice-models.html

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Dependencies

Package	Purpose
PyQt6 >= 6.6	GUI framework
pyqtgraph >= 0.13	Embedded plots
numpy >= 1.26	Numerical arrays
scipy >= 1.12	Filter design (student use)
PySpice >= 1.5	SPICE netlist + simulation
ngspice (system)	SPICE simulator backend

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CI

GitHub Actions runs on every push to main / develop and on all PRs:

• pyflakes syntax check on all .py files
• i18n completeness — warns if any language is missing keys
• XML validation of all .ui files

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License

GPL-3.0 © 2026 Universidad Iberoamericana