ams-sim

AMS Sim

Analog blocks must be verified across process corners, temperature, voltage, and mismatch. This skill plans the testbench matrix, generates the simulator decks, and triages results.

When to use

• After /analog-sizing produces a schematic
• After /analog-layout + extraction (post-layout)
• When mismatching is the suspected failure mode (Monte Carlo)
• Mixed-signal co-simulation with a digital controller (ngspice + Verilog-A, or Spectre APS)

Inputs

1. Schematic / netlist (.sp, .cir, .scs)
2. Device models from PDK (.lib / .scs)
3. Specs to verify (gain, BW, PSRR, CMRR, noise, slew, settling, offset)
4. Corner definition (FF/SS/TT/FS/SF × temp × supply)
5. Monte Carlo N (typical 500–5000 runs)

Analysis matrix

Analysis	Purpose
.op	DC operating point, bias validation
.dc	Sweeps (supply, input, parameter)
.ac	Gain, bandwidth, phase margin
.tran	Settling, slew, large-signal
.noise	Input-referred noise, SNR
.pss / .pac / .pnoise	Periodic steady-state (for RF / SC circuits)
.mc	Monte Carlo mismatch + process

The spec → required-analysis-subset mapping in this table is a frozen lookup, enforced by programs/ams_analysis_select.py — do NOT pick the analysis set by hand (two agents would otherwise pick different / incomplete subsets for the same spec list). Run it on the block's spec.json (or the project dir to scan analog/*/spec.json) and use the emitted analyses set:

python3 programs/ams_analysis_select.py <block>/spec.json
# -> {"analyses": [".op", ".ac", ".tran", ".noise"], "mapping": [...]}

It always selects .op (bias validation) when ≥1 measurable spec is present, adds .mc whenever any spec declares a mismatch / σ / yield concern, and FAILs honestly (exit 1) when a spec carries no recognizable measurable metric. Agent judgment is only needed to override an ambiguous / custom spec key the table does not recognize.

Workflow

1. Pick the analysis subset — enforced by programs/ams_analysis_select.py (see Analysis matrix)
2. Build deck with corner + MC sweeps
3. Run (ngspice / Xyce / Spectre / HSPICE)
4. Extract measurements via .meas statements — generated by programs/analog_meas_from_spec_gen.py
5. Tabulate corners × MC yield vs spec — enforced by programs/corner_yield_vs_spec_check.py (re-derives per-corner / per-spec PASS/FAIL from spec.json min/max limits + reports the worst, smallest-margin corner) and programs/analog_corner_sweep_check.py (gates ≥9-corner PVT count + all-spec-pass). Do NOT hand-tabulate the yield table — quote these programs' verdicts.
6. Flag failing corners — the worst corner is the worst_corner field from corner_yield_vs_spec_check.py; PVT-coverage gaps are classified by programs/corner_coverage_audit.py. Propose sizing or layout changes (agent judgment).
7. Hand off to re-sizing loop

Output format

• sim/<block>.sp (or equivalent) — simulator deck
• sim/<block>_results.md:
  • Spec table with pass/fail per corner — populated from corner_yield_vs_spec_check.py (per-corner / per-spec PASS/FAIL re-derived from spec.json limits), not graded by eye
  • MC yield percentage per spec — gated by analog_corner_sweep_check.py
  • Sensitivity list (which device / parameter dominates) — agent judgment
  • Suggested fixes — agent judgment

Tool prerequisites

Open source: ngspice (https://ngspice.sourceforge.io/), Xyce. Commercial: Cadence Spectre, Synopsys HSPICE, Silvaco SmartSpice.

Technical basis

Pelgrom mismatch model, corner methodology from PDK, Monte Carlo with correlated process parameters. Mixed-signal co-sim per Verilog-AMS / Verilog-A standards.

Handoff

• Failing corners → /analog-sizing (re-size)
• Layout-driven failures → /analog-layout
• Model issues → escalate to PDK team

Compliance gate (mandatory)

After producing your output, save it to a file and run:

python3 plugins/vibe-ic/_shared/skill_compliance_check.py \
    --requirements plugins/vibe-ic/skills/ams-sim/compliance.yaml \
    <your_output_file>

Exit 0 = PASS, exit 1 = FAIL with specific missing elements listed. compliance.yaml in the corresponding skill directory enumerates every required element of your output: section headers, metadata fields, handoff lines, tool invocations.

Your task is not complete until the audit returns PASS. Missing elements are the single largest source of skill-execution non-determinism across different agents.