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Elektronikprojekter

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Analogue Filter Calculator

Calculate analogue filter parameters directly on this page.
Graph colours Red = Magnitude, Blue = Phase.
Complex frequency: s = σ + jω = σ + j·2π·fo.

Passive Filters

RC Circuits


[a] [b] [c]
Bode Plot
Low-pass [a]
$H\(s\) = 1/{1 + s ⋅ R ⋅ C}$
$I_R = V/R \text" , " I_C = s ⋅ V ⋅ C$
$H\(s\) = {s ⋅ R ⋅ C}/{1 + s ⋅ R ⋅ C}$
$f_\o = 1/{2 ⋅ \π ⋅ R ⋅ C}$
Ω
F
Hz
s

RL Circuits


[a] [b] [c]
Bode Plot
High-pass [a]
$H\(s\) = {s ⋅ L}/{R + s ⋅ L}$
$I_R = V/R \text" , " I_L = V/{s ⋅ L}$
$H\(s\) = R/{R + s ⋅ L}$
$f_\o = R/{2 ⋅ \π ⋅ L}$
Ω
H
Hz

LC Circuits


[a] [b] [c]
Bode Plot
Resonant (peak) [a]
$I_L = V/{s ⋅ L} \text" , " I_C = s ⋅ V ⋅ C$
$H\(s\) = 1/{s^2 ⋅ L ⋅ C + 1}$
$H\(s\) = {s^2 ⋅ L ⋅ C}/{s^2 ⋅ L ⋅ C + 1}$
$f_\o = 1/{2 ⋅ \π ⋅ √{L ⋅ C}}$
H
F
Hz

Active Filters

OpAmp Low-pass/High-pass Circuits


[a] [b]
Bode Plot
Low-pass [a]
$H\(s\) = {-R_f}/R ⋅ 1/{1 + s ⋅ R_f ⋅ C}$
$H\(s\) = {-R_f}/R ⋅ {s ⋅ R_f ⋅ C}/{1 + s ⋅ R_f ⋅ C}$
$Gain = {-R_f}/R$
$f_\o = 1/{2 ⋅ \π ⋅ R_f ⋅ C}$
Ω
F
Hz

OpAmp Circuit with Complex Poles

Bode Plot
Band-pass with Q-factor
and gain, G
$H(s) = {-(R_1 ⋅ C)^{-1} ⋅ s}/{s^2 + 2 ⋅ (R_3 ⋅ C)^{-1} ⋅ s + ({R_1 ⋅ R_2}/{R_1 + R_2} ⋅ R_3 ⋅ C^2)^{-1}}$
R1 = Q/G
R2 = Q/(2 · Q2 - G)
R3 = 2 · Q
Resistor Scaling Factor = 1/(2 ·π· f0 · C)
Hz


F
Ω
Ω
Ω