RC/RLC Filter Calculator – Cutoff, Resonance, Q, Bode Plot

RC/RLC Filter Calculator

Cutoff, resonance, Q, bandwidth, and Bode magnitude plot for common filters.

Inputs
RC Low‑pass: 10 kΩ, 10 nF RC High‑pass: 1 kΩ, 100 nF RLC Band‑pass: R=100 Ω, L=10 mH, C=10 nF
Derived Values
Notes
RC fc = 1/(2πRC); magnitude at fc is −3 dB.
RLC (series) f0 = 1/(2π√(LC)), Q = (1/R)√(L/C), BW ≈ f0/Q.
Bode Magnitude (dB)
Log frequency axis; presets explore common scenarios.
About & Learning
What this is: RC/RL filters pass low or high frequencies; RLC band‑pass selects a narrow band around the resonance f0.
Why it’s used: smoothing sensor noise, anti‑aliasing, tone controls, EMI mitigation (RC/RL), and tuning/selectivity (RLC) in radios and instruments.
How to read the plot: The Bode magnitude (dB) uses a log frequency axis. The −3 dB point marks cutoff (RC/RL). For RLC, the peak near f0 and the −3 dB points define bandwidth (≈ f0/Q).
Learning tips: Connect time constants to cutoff (τ=RC, τ=L/R). Notice 20 dB/dec slopes beyond cutoff. Increasing R lowers Q and broadens the RLC peak; changing L or C shifts f0.
RC/RL/RLC Comparison
AspectRCRLRLC (series, BP)
Key parameterτ = RCτ = L/Rf0 = 1/(2π√(LC))
Cutoff/Resonancefc = 1/(2πRC)fc = R/(2πL)Q = (1/R)√(L/C), BW ≈ f0/Q
Roll‑off~20 dB/dec (1st order)~20 dB/dec (1st order)Rises then falls (~±20 dB/dec around f0)
Phase @ fc/f0±45° (LP/HP)±45° (LP/HP)≈0° at f0 (lead/lag either side)
Typical usesSmoothing, anti‑aliasing, toneDecoupling, current shapingTuning/selectivity, resonance
Note: Other RLC topologies (low/high/band‑stop, parallel RLC) have different transfer functions but share f0, Q relationships.

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About This Tool & Methodology

Analyzes RC/RLC circuits (time/frequency response) using SI units and standard circuit equations. Computes cutoff/ resonance and visualizes basic filter behavior.

Learning Outcomes

  • Understand time constants and resonance.
  • Relate component values to filter behavior.
  • Practice unit consistency and Bode intuition.

Authorship

  • Author: Anish Nath — Follow on X
  • Last updated: 2025-11-19

Trust & Privacy

  • Runs locally in your browser.
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