Circuit Draw

Noise-source symbols

Sources → V Noise / I Noise adds Razavi-style voltage/current noise sources, with editable v_n / i_n labels. See reference and export behavior. These are diagram symbols; simulation requires a simulator-specific noise model.

Related MCP server: ltagent-mcp

Small-signal circuits

Small Signal offers two-terminal gm · vgs, VCCS and VCVS sources plus ro, rπ, Cgs and Cgd. Only output terminals are drawn; the right-side display notation defines the controlling variable. Edit display as g_m v_gs, g_mb v_bs, or A_v v_ctrl, with SVG subscripts. gm current flows D to S, VCCS current out+ to out-, and VCVS output voltage follows its internal polarity marks.

For optional SPICE/Spectre export, bind the displayed voltage variable to named circuit nodes with controlPositive and controlNegative; gm defaults its negative reference to its S net. These fields add no graphic pins. Missing binding produces an explicit netlist comment and a check warning instead of invented nodes. gm/gain/value are numeric electrical values independent of display notation. Existing drawings with left control wires must remove those wires and bind the controlling voltage by name when migrating. No simulation or operating-point extraction is implied.

Transformer artwork is an original simplified rendition informed by actual schematic figures 2.4.2 and 2.4.6 in ISSCC 2010 Hua et al., also compared with ISSCC 2013 Brown et al. figure 25.2.4. It uses three rounded turns per winding, upper positive-polarity dots and concise k/Lp/Ls notation, with unchanged four-terminal coordinates and netlist semantics.

Schematic Canvas is a dependency-free, single-page web app for drawing analog / RF circuit schematics and turning them into real EDA output. It runs entirely in the browser, needs no build step and no external libraries, and can export your drawing as vector or raster graphics and as a runnable SPICE or Spectre netlist.

Features

• Analog/RF schematic editor — place and wire transistors, resistors, caps, inductors, transformers, op-amps, diodes, voltage sources, and supply/ground ports on a clean grid canvas.

• Fast, keyboard-first interaction — insert (I), wire (W), text (T), arrow/line/ rect/circle annotations, rotate (R), mirror (Shift+R / Ctrl+R), undo/redo (Ctrl+Z).

• Smart wiring — T-junctions and device pins landing on a wire interior are recognized as real connections; pure crossings stay disconnected, per schematic convention.

• One-click export — SVG, PNG, JPG, PDF (vector via a print window), plus SPICE and Spectre netlists with correct pin ordering and subcircuit prefixes.

• Built-in component library — a broad set of analog symbol primitives, plus templates such as a 5-transistor OTA.

• Design-rule check — a netlist check report flags floating pins, dangling wires, and missing supply/ground ports before you export.

• Vendor-neutral formats — generated netlists work with Spectre and generic SPICE simulators.

Getting started

No installation, no build.

Easiest (Windows): double-click start-dev.bat — it starts the no-cache dev server and opens the app in your browser.

Or manually:

# Recommended — local dev server (sends no-cache headers, so you always get the latest code)
python serve.py            # serves http://127.0.0.1:8642
python serve.py 8655       # any port

Why not just double-click index.html? Opening the file directly (file://) works, but the browser can keep serving a cached copy of app.js, so edits look like they never took effect. The dev server sends no-store headers, which makes that impossible — and the build stamp in the status bar tells you at a glance which version is running. If you do open index.html directly and changes don't show, hard-refresh (Ctrl+F5).

If that port is already serving, serve.py tells you so and exits rather than silently sharing the port — start the next one up, or just open the instance already running.

With Node.js you can also run it through npm:

npm start        # == python serve.py
npm test         # all topology, geometry and MCP regression tests

When you change JS/CSS during development and the browser seems to keep the old code, hard-refresh (Ctrl+F5). The ?v=N query strings on the index.html script/style tags are a cache-busting version counter, and APP_VERSION in app.js keeps the on-screen build stamp in sync.

Usage

Use the File ▾ menu for new/open/save projects and for Export. Use Netlist ▾ to view the netlist, the instance table, or the check report.

Export

• SVG — vector, self-contained (styles are embedded so it renders identically outside the app).

• PNG — raster snapshot of the canvas.

• JPG — high-quality raster snapshot with a white background.

• PDF — vector quality; opens a print window (no dependencies).

• SPICE / Spectre — netlists with correct pin ordering, port/ground naming, and subcircuit prefix conventions.

Testing

The netlist engine ships with a dependency-free unit suite driven by Node's built-in test runner:

npm test

Tests cover topology (T-junctions, crossings, splits), pin/net naming, floating detection, and SPICE/Spectre/instance-table output. Requires Node 18+.

Regression tests also cover exact 90-degree pin transforms, multi-frame wire dragging, safe imports, old VDD Rail migration, MCP stdio calls, backups and local-editor startup. Run all tests with npm test.

Recovery and safe imports

The canvas starts empty on ordinary page loads. It retains the last recovery copy: use File → Restore Recovery Copy to restore it after refresh or reopening the page at the same origin. The status says Recovery copy saved, distinguishing it from Save Project, which downloads JSON. Unsaved edits trigger a browser close warning. Recovery is scoped to the browser origin; save JSON for durable copies or changing ports. Invalid JSON projects are validated before the current drawing is replaced.

The power library contains a single VDD symbol. Old vdd_rail entries load as VDD with the same electrical pin position. New templates use VDD.

Circuit Draw Codex plugin

The plugin bundles the existing editor, a dependency-free Node.js stdio MCP server and the draw-circuit skill. It needs Node 18+ on PATH, no API key and no npm install. The plugin and its bundled component artwork are released under the MIT License.

The skill uses two actual subagents in this order:

1. Drawing agent writes the first editable JSON + SVG, then stops.

2. Review agent checks exact pin/net topology and inspects a real rendered screenshot.

3. After review completes, the drawing agent writes a separate revision and change log.

4. Review agent rechecks the revision. The coordinator delivers only after both topology and visual gates pass, or explicitly reports remaining blockers.

Reviewed drafts are kept. The reviewer never edits the circuit. The two role instructions are in skills/draw-circuit/agents/. Hosts without subagent support must disclose the limitation instead of claiming independent agents ran.

Build the source-only package and install from the local marketplace:

node scripts/package-plugin.js
codex plugin marketplace add .
codex plugin add circuit-draw@circuit-tools
codex plugin list

Restart Codex or start a fresh local chat if the new plugin tools are not yet visible. Example request:

使用 $draw-circuit 绘制五管 OTA，让校验 agent review 完再由绘图 agent 修改，电源统一用 VDD。

The nine MCP tools are:

All paths are absolute. Existing output files require overwrite: true; overwritten files receive timestamped backups. Browser Save Project downloads JSON and does not write back to the loaded source file. MCP export is SVG/netlist/JSON; use browser export for PNG/JPG/PDF. The local editor URL expires after 30 minutes.

If the MCP is not loaded, the skill can call the same engine through a structured args file:

node scripts/circuit-cli.js create_project --args-file D:\work\create-args.json

Example args: {"path":"D:/work/ota.json","name":"Five-transistor OTA","template":"ota5"}. Netlist generation does not simulate the circuit. Models/subcircuit definitions are external; VDD markers name a net but do not create a voltage source. Three-terminal MOS bulk is tied to source in the generated netlists.

Project structure

.
├── index.html          # app shell (menus, toolbars, dialogs)
├── app.js              # main app: canvas, tools, selection, wires, undo/redo
├── components.js       # component symbol library (SVG primitives)
├── templates.js        # built-in schematic templates (e.g. 5-transistor OTA)
├── netlist.js          # SPICE / Spectre netlist generation + check report
├── exporter.js         # SVG / PNG / JPG / PDF export
├── netlist.test.js     # unit tests (Node 18+, no dependencies)
├── style.css           # styling
├── serve.py            # optional no-cache dev server
├── package.json        # metadata + npm scripts
└── LICENSE             # MIT

Publishing note

The three binary Visio stencils (Analog Circuit.vss, RFIC_lib.vss, RFsys_lib.vss), the verify_ota.png.jpg screenshot, and _site_extra_chips.json were source/scrape artifacts used while building the component library. They are not part of the runtime app and are intentionally excluded from this repository via .gitignore. If you want to publish a demo screenshot, add your own image under docs/ and link it above.

Contributing

Contributions are welcome — please read CONTRIBUTING.md first. The short version:

1. Open an issue first for anything non-trivial.

2. Keep the app dependency-free — no build step, no CDN/framework imports.

3. Add a test for any netlist/topology change (netlist.test.js).

4. Bump the ?v=N cache-busting query and APP_VERSION when you touch JS/CSS.

Release history lives in CHANGELOG.md.

License

This repository, including the editor, MCP server, CLI, skills and bundled component artwork, is released under the MIT License.

The symbol artwork in components.js originated from Analog Canvas by 张托肯, 清华大学. On 2026-10-23, the project maintainer confirmed permission to release these symbols with this plugin under MIT. This records the maintainer's confirmation; an original authorization document is not included in this repository. Preserve the source attribution and MIT license notice when redistributing.

致谢 / Acknowledgements

致谢清华大学张托肯。感谢其提供的 Analog Canvas 电路符号与绘图工作，为本项目提供了重要基础。