CALCULATORS / ANALOG CIRCUITS AND FILTERS

Passive RC/RL filter calculator

Ideal unloaded RC low-pass at one sinusoidal frequency.

analog-passive-filter.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

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

Scenario	cornerHz	magnitude
	1591.55	0.846733
	1989.44	0.893476

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.

passband gain target0.85 ✓ passes

BASELINE INPUTS

resistance1000 ohmcapacitance100 nFfrequency1000 Hz

CALCULATED

corner1591.5 Hz

magnitude0.84673

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Passive RC/RL filter
# Scope: Ideal unloaded RC low-pass at one sinusoidal frequency.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

resistance = 1000 ohm
capacitance = 100 nF
frequency = 1000 Hz

corner := 1/(2*pi*resistance*capacitance) [Hz]
magnitude := 1/sqrt(1+(frequency/corner)^2)

check passband gain target: magnitude >= 0.7

scenario alternative: resistance = 800 ohm

Calculated from your source · not saved

Baseline · Baseline

passband gain target0.85 ✓ passes

alternative · alternative

passband gain target0.89 ✓ passes

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.

corner: corner = 1/(2*pi*resistance*capacitance) [Hz]
magnitude: magnitude = 1/sqrt(1+(frequency/corner)^2)

Original worked example

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

Given

resistance: 1000 ohm
capacitance: 100 nF
frequency: 1000 Hz

Calculated

corner: 1591.55 Hz
magnitude: 0.846733

Assumptions and limits

Ideal unloaded RC low-pass at one sinusoidal frequency.

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: Passive RC/RL filter. Inputs: topology; values; source/load impedance. Outputs: cutoff; gain and phase. Model scope: Lumped small-signal models within device operating ranges. 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: topology, values, source/load impedance
Outputs: cutoff, gain and phase
Modes: calculate, compare, sweep
Drawing: Schematic and Bode plot

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