sim

name: sim description: > Circuit simulation and pre-fabrication validation. Trigger on: "simulate", "run simulation", "spice", "check stability", "ripple analysis", "phase margin", "power supply simulation", "AC analysis", "transient analysis". Includes automated SPICE simulation via ngspice, RF chain analysis (scikit-rf), power/clock analysis (PyLTSpice), and PCB EM (openEMS FDTD). Run before ordering to validate performance before spending on prototypes.

Auto-Detection

Before running simulations, discover existing projects in the current directory:

python -m circuit_weaver discover --json

If projects are found, select the target project automatically (most recently modified, or ask the user if multiple exist). Use the project's design.yaml and any existing SPICE models in spice_models/ directory.

Quick Start (Automated)

Run automated simulations on any Circuit Weaver design:

# Run all simulations (power, signal, thermal)
python -m circuit_weaver simulate design.yaml -o ./sims

# Run only power supply simulations
python -m circuit_weaver simulate design.yaml -o ./sims --type power

# Fetch SPICE models first, then simulate
python -m circuit_weaver fetch-spice design.yaml
python -m circuit_weaver simulate design.yaml -o ./sims --model-dir ./spice_models

# JSON output for programmatic use
python -m circuit_weaver simulate design.yaml -o ./sims --json

The simulator auto-detects power regulators, filters, and op-amps from the design spec and generates appropriate SPICE netlists + analysis cards.

Three-Layer Stack (Advanced / Manual)

Layer 1 -- RF Chain (scikit-rf)

Cascades S2P files (filters, LNAs, mixers, PCB traces) to compute end-to-end insertion loss, return loss, and noise figure across the signal chain.

import skrf as rf

bpf   = rf.Network("sims/rf/filters/bpf_2450.s2p")
lna   = rf.Network("sims/rf/lna/lna.s2p")
trace = rf.Network("sims/rf/traces/microstrip_50ohm_5mm.s2p")

chain = bpf ** lna ** trace
print(f"IL @ 2.45 GHz: {-chain.s21.db[freq_idx]:.1f} dB")
print(f"NF: {chain.nf(T=290)[freq_idx]:.2f} dB")

S2P sources (priority order):

1. Vendor-measured data (request from manufacturer -- best)
2. Datasheet typical curves extracted with WebPlotDigitizer
3. Synthetic models (document clearly -- mark as unvalidated)

Simulation targets (fill in per project):

Layer 2 -- Power / Clock (LTspice / PyLTSpice)

Transient and AC analysis of power supply circuits and clock distribution. Validates regulator stability, output ripple, PDN impedance, and load response.

from PyLTSpice import LTspice

lt = LTspice("sims/power/buck_3v3.asc")
lt.run()
vout = lt.get_trace("V(vout)")
ripple_mv = (vout.max() - vout.min()) * 1000
print(f"Output ripple: {ripple_mv:.1f} mV")

Subcircuits to simulate (fill in per project):

SPICE model sources:

• Manufacturer SPICE models (from product page -- preferred)
• IBIS models for digital ICs (use ibis2spice if needed)
• LTspice built-in library for generic models

Layer 3 -- PCB EM (openEMS FDTD)

Full-wave electromagnetic simulation for antenna performance, via transitions, edge coupling, and shielding effectiveness. Most expensive -- run selectively.

Run Layer 3 for:

• On-board antennas (patch, meandered monopole, chip antenna matching)
• Via transitions on high-speed interfaces (> 5 Gbps)
• Near-field coupling characterization between modules
• Shielding can effectiveness

Skip Layer 3 for:

• Standard passive components
• Well-characterized reference designs validated by manufacturer

# openEMS requires platform binary + Python bindings
# See: https://openems.de/start/
python3 sims/em/antenna/run_sim.py

Directory Structure

sims/
  rf/         -- scikit-rf scripts + S2P files
  power/      -- LTspice .asc schematics + PyLTSpice runner scripts
  em/         -- openEMS geometry definitions + run scripts
  results/    -- output plots and summary JSONs (add to .gitignore if large)

Pre-Fab Simulation Checklist

• Layer 1: All RF paths passing insertion loss targets
• Layer 1: Noise figure budget within sensitivity requirement
• Layer 2: All regulators stable (phase margin > 45 deg)
• Layer 2: Output ripple < specification on all rails
• Layer 2: PDN impedance < target at operating frequency
• Layer 3: Antenna efficiency > target (if on-board antenna)
• Layer 3: Via transitions characterized for high-speed interfaces

Requirements

pip install scikit-rf PyLTSpice
# openEMS: see https://openems.de/start/ for platform-specific install