Circuit Explorer

RC Low-Pass Filter

The RC low-pass filter is one of the most fundamental circuits in electronics. It passes low frequencies while attenuating high frequencies, with a characteristic -20 dB/decade roll-off above the cutoff frequency.

fc = 1/(2πRC)

φ = -arctan(f/fc)

First-Order Filter

Circuit Schematic

Interactive Diagram

Hover over components for explanations

Adjust Values

Component Controls

Resistance (R)1.00 kΩ

10.0 Ω1.00 MΩ

Sets impedance level and affects time constant

Capacitance (C)100.0 nF

1.00 pF100 µF

Stores energy and determines frequency response

Quick Presets

Calculated Values

Filter Characteristics

Cutoff Frequency1.59 kHz

fc = 1/(2πRC)

Time Constant100.00 µs

τ = R × C

Phase at fc-45.00 °

φ(fc) = -45°

Gain at fc-3.00 dB

|H(fc)| = -3dB

Bode Plot

Magnitude Response

Shows how the filter attenuates signals at different frequencies

-20 dB/decade slope above fc

-3dB at cutoff

Bode Plot

Phase Response

Shows the phase shift between input and output signals

Phase shift from 0° to -90°

-45° at cutoff

Learn More

How It Works

At Low Frequencies

The capacitor acts like an open circuit (high impedance). Most of the input voltage appears at the output, giving unity gain.

At High Frequencies

The capacitor acts like a short circuit (low impedance). The output is shunted to ground, attenuating the signal.

At Cutoff Frequency

The capacitive reactance equals the resistance (Xc = R). Output power is half (-3dB) and phase shift is -45°.

Time Constant

τ = RC determines the filter's step response. After 5τ, the output reaches ~99% of its final value.