Analog Extraction Resim

After analog layout in Magic, extracts parasitic RC and re-simulates across PVT corners to check for layout-induced performance degradation. Compares pre-layout vs post-layout results and flags regressions.

When to use

• Step A7 of the analog track
• After analog-layout has produced a Magic .mag file
• When the user asks "did the layout hurt my bandwidth?"

Inputs

1. analog/<block>/layout.mag — Magic layout file
2. analog/<block>/corner_results.json — pre-layout SPICE results (baseline)
3. analog/<block>/spec.json — specs for pass/fail comparison
4. PDK (gf180 or sky130)

Workflow

1. Extract parasitics — emit/validate the Magic parasitic-RC TCL with programs/magic_extract_spice_emit.py (do not hand-write the recipe):

   # emit the deterministic .mag -> RC-annotated .subckt extraction TCL
   python3 programs/magic_extract_spice_emit.py --block <block> \
       --out-spice analog/<block>/<block>_extracted.spice --out extract.tcl
   # or validate an existing extraction TCL (FAILs if it omits `extract all`
   # or `ext2spice lvs` — the two silent causes of a vacuous 0% degradation)
   python3 programs/magic_extract_spice_emit.py --validate extract.tcl
   

   Then run it via eda_extraction (or magic). Output: analog/<block>/<block>_extracted.spice.

   The fixed load / extract all / ext2spice lvs / ext2spice recipe is enforced by programs/magic_extract_spice_emit.py (distinct from the GDS-read + port-promote LVS recipe in magic_port_extract_emit.py).

2. Re-simulate with extracted netlist:

   • Replace ideal subcircuit with extracted netlist in testbench
   • Run eda_spice_corner with same corners as pre-layout
   • Output: analog/<block>/post_layout_corner_results.json

3. Compare pre vs post — run the deterministic checker; do not re-grade by hand:

   python3 programs/analog_pre_vs_post_layout_check.py <project> --json
   

   It computes per-metric per-corner degradation (post - pre) / pre × 100% and classifies it against the canonical degradation bands, which the program owns (single source of truth — see "Degradation thresholds" below). Do NOT hardcode a different ERROR/WARNING cutoff in your report; quote the program's verdict.

   • Typical degradation sources:
     • Bandwidth reduction (parasitic C on high-impedance nodes)
     • Gain reduction (parasitic R in signal path)
     • Increased noise (parasitic coupling)

Output format

analog/<block>/pre_vs_post.json

{
  "block_name": "ldo_1v8",
  "pre_layout_file": "corner_results.json",
  "post_layout_file": "post_layout_corner_results.json",
  "comparison": {
    "gain_db": {"pre": 62.3, "post": 58.1, "degradation_pct": -6.7, "status": "OK"},
    "ugb_mhz": {"pre": 11.2, "post": 7.5, "degradation_pct": -33.0, "status": "ERROR"},
    "vout_dc": {"pre": 1.8002, "post": 1.7998, "degradation_pct": -0.02, "status": "OK"}
  },
  "worst_degradation": {"metric": "ugb_mhz", "pct": -33.0},
  "overall_status": "NEEDS_RELAYOUT"
}

Degradation thresholds

Enforced by programs/analog_pre_vs_post_layout_check.py (single source of truth — ≤20% OK / >20% WARNING / >30% ERROR→NEEDS_RELAYOUT). Quote the program's verdict; do not restate a conflicting cutoff. If the policy must change, change it in the program (one place) so SKILL.md and runtime never drift.

Do not

• Do not skip extraction and go straight to hardmacro — parasitic RC is the #1 cause of analog silicon failure
• Do not compare only TT corner — worst-case degradation often appears at SS+hot
• Do not ignore capacitive loading on compensation nodes (Cc) — parasitics add to Cc

Handoff

Branch on the overall_status field emitted by programs/analog_pre_vs_post_layout_check.py (deterministic, not a judgment call):

• OK / WARNING → analog-hardmacro-gen (Step A8)
• NEEDS_RELAYOUT → back to analog-layout (Step A5)
• post_layout_corner_results.json → analog_pre_vs_post_layout_check gate

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/analog-extraction-resim/compliance.yaml \
    <your_output_file>

Exit 0 = PASS, exit 1 = FAIL with specific missing elements listed.

Your task is not complete until the audit returns PASS.