Second Order LC Low Pass Filter Calculator

Calculate resonant frequency(f_r)

Inputs:
L: mH µH nH
C: µF nF pF
Q:

Theoretical Results:
f_r:
X_L:
R:

Calculate L:
Inputs:
f_r: Hz KHz MHz
C: µF nF pF

Theoretical Results:
L: Formula Used:
$L =\frac{1}{4 \pi^2 f_{r}^2 C}$

Calculate C:

Inputs:
f_r: Hz KHz MHz
L: mH µH nH

Theoretical Results:
C:
Formula Used:
$C =\frac{1}{4 \pi^2 f_{r}^2 L}$

Contents

1. About LC Parallel Resonant Circuit Calculator
   1. Notes on Second Order LC Low Pass Filter Calculator

About LC Parallel Resonant Circuit Calculator

The above online calculator for second order LC low pass filter calculates the cutoff frequency and Q from given inductor, capacitor and load resistor values or calculate inductor, capacitor values from given cutoff frequency.

Notes on Second Order LC Low Pass Filter Calculator

The Q of the filter is given by, $$Q=\frac{R}{X_L}$$ where, the inductor reactance $X_L$ is calculated at the resonant frequency. When Q is high the gain will increase and in frequency response graph we will see peak. The following graph illustrates frequency response of LPF when Q is high.

To get maximally flat response(Butterworth Response), Q should be 0.707 and at this Q=0.707 value the frequency response of the LC low pass filter will be like the following,

Higher order LC LPF

The quality factor Q of the LC parallel tank is given by the following equation:

$Q=\frac{Energy \space  stored \space in \space Reactive \space component}{Energy \space dissipated}$ 

or, $Q=\frac{X_C}{R_w}=\frac{X_L}{R_w}$

Some example usage of this online LC parallel resonant circuit calculator are as follows.

- How does Single Diode Modulator Circuit work?
- Simple Amplitude Modulation (AM) circuit using Single Diode Modulator