Engineering
RC Low-Pass Filter Calculator
Design RC low-pass filters for signal conditioning, noise filtering, and anti-aliasing in analog circuits.
RC Filter Design Guide
Time constant (τ = RC): The time for voltage to decay to 37% after disconnect. After 5τ, voltage drops to 0.67%. Use τ to estimate filter settling time.
Cutoff frequency (Fc): The −3dB point where signal amplitude drops to 70.7%. Above Fc, attenuation increases at 20 dB/decade (−6 dB per octave).
Loading effects: Connecting a load changes the effective RC time constant. Always account for the load impedance when designing high-impedance filters.
Common Cutoff Frequencies by Application
| Application | Typical Fc | Reason |
|---|---|---|
| Audio line filtering | 20 kHz | Above human hearing |
| ADC anti-alias | Fs ÷ 2.5 | Below Nyquist frequency |
| Supply ripple filtering | 10–100 Hz | Below 120/100 Hz ripple |