Electrical Short¶

File: pics/elec.pic.yml

Error caught: short — two routes on the metal layer overlap, shorting two independent nets.

Error type: LVS.short

Expected: ok=False, error_count=2 (1 short + 1 missing_in_schematic net group derived from the short)

import tempfile
from copy import deepcopy
from pathlib import Path

import elvis
import gdsfactory as gf
from IPython.display import Markdown
from kwasm import Tool, show

gf.gpdk.PDK.activate()

PICS = Path("../pics")
BUILD_GDS = Path("../build/gds")
BUILD_GDS.mkdir(parents=True, exist_ok=True)
PIC = PICS / "elec.pic.yml"

Schematic¶

Pads connected by route_bundle_electrical routes. Two of the routes overlap on the metal layer, creating a short between nets that should be independent.

schematic = elvis.load_schematics(PIC)
schematic

{'elec': {'instances': {'pad1': {'component': 'pad', 'settings': {}},
   'pad2': {'component': 'pad', 'settings': {}},
   'pad3': {'component': 'pad', 'settings': {}},
   'pad4': {'component': 'pad', 'settings': {}}},
  'routes': {'electrical': {'links': {'pad1,e3': 'pad2,e1'},
    'routing_strategy': 'route_bundle_electrical',
    'settings': {'allow_layer_mismatch': False,
     'allow_type_mismatch': False,
     'allow_width_mismatch': False}},
   'electrical2': {'links': {'pad3,e3': 'pad4,e3'},
    'routing_strategy': 'route_bundle_electrical',
    'settings': {'allow_layer_mismatch': False,
     'allow_type_mismatch': False,
     'allow_width_mismatch': False,
     'radius': 10}}},
  'ports': {},
  'placements': {'pad1': {'x': 0, 'y': 0, 'dx': -98.125, 'dy': -19.273},
   'pad2': {'x': 0,
    'y': 0,
    'dx': 349.71,
    'dy': -394.94,
    'rotation': 0,
    'mirror': False},
   'pad3': {'x': -98.125,
    'y': -19.273,
    'dx': -97.005,
    'dy': -423.277,
    'rotation': 0,
    'mirror': False},
   'pad4': {'x': 0,
    'y': 0,
    'dx': 137.75,
    'dy': -124.39,
    'rotation': 0,
    'mirror': False}}}}

Build from schematic¶

gds_path = BUILD_GDS / "elec.gds"
c = gf.read.from_yaml(schematic["elec"])
c.write_gds(gds_path)
show(gds_path, netlist=PIC, tools=[Tool.FIT_ALL, Tool.INSTANCE_PORTS])

LVS Results¶

rdb = elvis.lvs_rdb(
    gds_path,
    schematic,
    short_layers=[(49, 0)],
    equivalent_ports={"pad": ["pad", "e1", "e2", "e3", "e4"]},
)
lyrdb = Path(tempfile.gettempdir()) / "elec.lyrdb"
rdb.save(str(lyrdb))
show(gds_path, lyrdb=lyrdb, netlist=PIC, tools=[Tool.FIT_ALL, Tool.INSTANCE_PORTS])

Errors in detail:

print(f"ok={rdb.num_items() == 0}, error_count={rdb.num_items()}")
Markdown(elvis.error_summary(rdb))

ok=False, error_count=2

Geometric short detection via short_layers keyword¶

Pass short_layers=[(layer, datatype)] to enable polygon-level short checking. Elvis runs a four-step pipeline:

1. Chain building — instances are grouped into chains:
2. Each connected sequence of 2-port route instances (straights, bends, tapers) forms one chain, named after its reference-component endpoints, e.g. "pad1,e3 -> pad2,e2".
3. Each multi-port reference component (splitter, combiner, pad, …) is its own single-instance chain.
4. Bare polygons drawn directly in the top cell are collected into a single top-cell polygons chain.
5. Polygon extraction — GDS boundaries on the specified layer are extracted per instance and grouped by chain. Each chain's polygons are unioned into a single MultiPolygon.
6. Overlap detection — all pairs of chains are tested for polygon intersection. Overlaps that fall exactly at port locations (where chains legitimately share a boundary) are filtered out.
7. Schematic-aware suppression — a detected short is suppressed if all cross-chain port pairs it implies are already declared in the schematic (see the Fix section below for details).

Layer (49,0) is the metal layer in GDSFactory's generic PDK.

Fix¶

Route from pad1 to pad2 by going around pad4. The easiest way to achieve this is by adding a start_straight_length to the route leaving from pad:

schematic2 = deepcopy(schematic)
schematic2["elec"]["routes"]["electrical"]["settings"]["start_straight_length"] = 300
c2 = gf.read.from_yaml(schematic2["elec"])
c2.write_gds(gds_path)
rdb = elvis.lvs_rdb(
    gds_path,
    schematic2,
    short_layers=[(49, 0)],
    equivalent_ports={"pad": ["pad", "e1", "e2", "e3", "e4"]},
)
lyrdb = Path(tempfile.gettempdir()) / "elec.lyrdb"
rdb.save(str(lyrdb))
show(gds_path, lyrdb=lyrdb, netlist=PIC, tools=[Tool.FIT_ALL])

Another Fix¶

If the short is intentional one can add (often just one of) the missing nets to the schematic to fix it too.

schematic3 = deepcopy(schematic)
schematic3["elec"]["nets"] = [
    # just one should be enough,
    # because after adding it it makes the unconnected nets equivalent
    {"p1": "pad1,e3", "p2": "pad3,e3"},
    # {'p1': 'pad2,e1', 'p2': 'pad3,e3'},
    # {'p1': 'pad1,e3', 'p2': 'pad4,e3'},
    # {'p1': 'pad2,e1', 'p2': 'pad4,e3'},
]
c2 = gf.read.from_yaml(schematic3["elec"])
c2.write_gds(gds_path)
rdb = elvis.lvs_rdb(
    gds_path,
    schematic3,
    short_layers=[(49, 0)],
    equivalent_ports={
        "pad": ["pad", "e1", "e2", "e3", "e4"],
    },
)
lyrdb = Path(tempfile.gettempdir()) / "elec.lyrdb"
rdb.save(str(lyrdb))
show(gds_path, lyrdb=lyrdb, netlist=PIC, tools=[Tool.FIT_ALL])

Why it works — Transitive Net Closure¶

Adding all four reported nets is the clearest and most explicit approach. But even adding one of them is sufficient, because Elvis builds the transitive closure of all declared connections before checking cross-pairs.

Take pad1,e3 ↔ pad3,e3 as an example. This single net bridges the two otherwise separate route groups.

After transitivity: {pad1,e3, pad2,e1, pad3,e3, pad4,e3, pad1,e3} — one equivalence class. Every cross-pair is now "in the schematic", so the short is suppressed.

Why it matters¶

Electrical shorts on metal routing layers cause catastrophic failures: two independent nets merge into one, and both signals fight each other. Dense pad arrays are especially prone to routing shorts because routes are packed tightly and DRC rules alone may not catch a short that falls within design rules. Elvis's chain-based short detection finds overlaps that are electrically meaningful, not just geometrically close.