CALCULATORS / PCB INTERCONNECT AND PACKAGING

Differential impedance from odd-mode impedance calculator

Differential impedance from supplied odd-mode impedance; coupling must come from stackup solver.

pcb-differential-pair.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	differentialohm	errorohm
	100	0
	80	20

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

impedance tolerance0.00 ohm✓ passes

BASELINE INPUTS

oddMode50 ohmtarget100 ohmtolerance10 ohm

CALCULATED

differential100 ohm

error0 ohm

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Differential-pair impedance screening
# Scope: Differential impedance from supplied odd-mode impedance; coupling must come from stackup solver.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

oddMode = 50 ohm
target = 100 ohm
tolerance = 10 ohm

differential := 2*oddMode [ohm]
error := abs(differential-target) [ohm]

check impedance tolerance: error <= tolerance

scenario alternative: oddMode = 40 ohm

Calculated from your source · not saved

Baseline · Baseline

impedance tolerance0.00 ohm ✓ passes

alternative · alternative

impedance tolerance20.00 ohm × fails

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

differential: differential = 2*oddMode [ohm]
error: error = abs(differential-target) [ohm]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

odd mode: 50 ohm
target: 100 ohm
tolerance: 10 ohm

Calculated

differential: 100 ohm
error: 0 ohm

Assumptions and limits

Differential impedance from supplied odd-mode impedance; coupling must come from stackup solver.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Differential-pair impedance screening. Inputs: pair geometry; stackup; dielectric data; model. Outputs: odd/even-mode and differential estimates. Model scope: Explicit stackup and trace/via geometry; empirical models identified. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: pair geometry, stackup, dielectric data, model
Outputs: odd/even-mode and differential estimates
Modes: calculate, compare, sweep
Drawing: Layer viewer and cross section

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS