Filter Calculators

contempl8.io →

Interactive calculators that design and analyse analog filters — enter component values for analysis, or a target cutoff and damping to synthesize the parts, with live Bode, Nyquist, and time-domain plots.

Inputs accept engineering notation: SI suffixes 10k 2.2M 100n 1u 47p 100m 1G, RKM 4k7 = 4700, 2u2 = 2.2µF, 4R7 = 4.7Ω, plus plain 4700 and scientific 1e-6.

Guide

How to Read the Graphs

New to Bode, group-delay, Nyquist, pole-zero, impulse and step plots? Start here — each explained with live examples.

RC Filters

RC Low-Pass

First-order passive low-pass. H(s) = 1 / (1 + sRC).

RC High-Pass

First-order passive high-pass. H(s) = sRC / (1 + sRC).

LR Filters

LR Low-Pass

First-order passive low-pass (L/R). H(s) = 1 / (1 + s·L/R).

LR High-Pass

First-order passive high-pass (L/R). H(s) = s·L/R / (1 + s·L/R).

RLC Filters

RLC Low-Pass

Second-order series RLC, output across C.

RLC High-Pass

Second-order series RLC, output across L.

RLC Band-Pass

Second-order series RLC, output across R.

RLC Band-Stop

Second-order series RLC notch, output across L+C.

RLC Band-Pass (parallel)

Parallel R‖L‖C tank band-pass.

RLC Band-Stop (parallel)

Parallel R‖L‖C tank notch.

Sallen-Key Active Filters

Sallen-Key Low-Pass

Active 2nd-order VCVS low-pass; design from spec, gain K = 1 + Rb/Ra.

Sallen-Key High-Pass

Active 2nd-order VCVS high-pass; design from spec, gain K = 1 + Rb/Ra.

Sallen-Key Band-Pass

Active 2nd-order VCVS band-pass with gain K = 1 + Rb/Ra.

3rd-Order Sallen-Key Low-Pass

1st-order RC + 2nd-order Sallen-Key; Butterworth/Chebyshev/Bessel.

3rd-Order Sallen-Key High-Pass

1st-order RC + 2nd-order Sallen-Key; Butterworth/Chebyshev/Bessel.

Multiple-Feedback Active Filters

MFB Low-Pass

2nd-order multiple-feedback low-pass (inverting); design from spec.

MFB High-Pass

2nd-order multiple-feedback high-pass (inverting); design from spec.

MFB Band-Pass

Active 2nd-order multiple-feedback band-pass (inverting).

3rd-Order MFB Low-Pass

1st-order RC + 2nd-order multiple-feedback; design from spec.

3rd-Order MFB High-Pass

1st-order RC + 2nd-order multiple-feedback; design from spec.

1st-Order Active Filters

1st-Order Active Low-Pass

Single op-amp inverting low-pass. H(s) = -(R2/R1)/(1 + sR2C).

1st-Order Active High-Pass

Single op-amp inverting high-pass. H(s) = -sR2C/(1 + sR1C).

All-Pass Filters

1st-Order All-Pass

Flat magnitude, frequency-dependent phase. H(s) = (1 - sRC)/(1 + sRC).

2nd-Order All-Pass

Active 2nd-order phase equalizer; mirror-image zeros/poles.

State-Variable Filters

State-Variable Low-Pass

KHN two-integrator-loop low-pass; independent f₀/Q.

State-Variable High-Pass

KHN two-integrator-loop high-pass; independent f₀/Q.

State-Variable Band-Pass

KHN two-integrator-loop band-pass; independent f₀/Q.

Biquad Filters

Biquad Low-Pass

Tow-Thomas two-integrator biquad low-pass (inverting).

Biquad Band-Pass

Tow-Thomas two-integrator biquad band-pass (inverting).

Notch Filters

Twin-T Notch

Passive RC notch (Q = 0.25). H(s) = (1 + s²R²C²)/(1 + 4sRC + s²R²C²).

Fliege Notch

Active twin-amplifier notch with tunable f₀ and Q.

2nd-Order CR Filter

RC Band-Pass (two-stage)

Cascaded RC high-pass × low-pass wideband band-pass.

Op-amp Building Blocks

Inverting Amplifier

Vout/Vin = -Rf/Rin.

Non-Inverting Amplifier

Vout/Vin = 1 + Rf/Rg.

Summing Amplifier

Two-input inverting summer; Vout = -(Rf/R1·V1 + Rf/R2·V2).

Difference Amplifier

Single op-amp subtractor; gain = R2/R1.

Instrumentation Amplifier

3-op-amp; gain = (1 + 2R1/Rg)(R3/R2).

Ideal Integrator

Vout/Vin = -1/(s·Rin·C); -20 dB/dec.

Ideal Differentiator

Vout/Vin = -s·Rf·C; +20 dB/dec.

Filter Designer (synthesis)

Filter Designer

Butterworth / Chebyshev / Bessel — LP/HP/BP/BS, with active + LC-ladder realizations.