# CLC Filter Calculator

A CLC filter is comprised of a Capacitor-Inductor-Capacitor in a pi π configuration. This creates a low pass filter (LPF).

This tool calculates values for each of the components based on cutoff frequency values.

Enter cut-off frequency for the LPF and desired impedance to find the Inductor (L) and capacitor (C) values for this Pi network.

## Background

### Low-Pass Filter

A low-pass filter (LPF) allows frequencies below a specific cut-off frequency to pass through while attenuating higher frequencies.

The picture below shows an ideal low pass filter. Signals with frequency less than the cut-off frequency Fc pass through while signals with higher frequencies are blocked or attenuated.

In practice a low pass filter doesn’t have the ideal brick wall characteristic shown in the picture above. Instead it has a cut off frequency which is where the signal is attenuated by 3 dB (also called insertion loss). After that it rolls off as shown in the picture below. Attenuation increases with frequency.

### How to design a CLC Filter

A LPF consists of one series inductor (L1) and two identical shunt capacitors (C1=C2) as shown in the picture below.

The formula for the calculation is given below. Inductor and Capacitor values are calculated from the characteristic impedance and Fc.

L = Zo/(π*Fc)

C = 1/(Zo*π*Fc)

### Example Calculation

A low pass filter with 500 MHz cutoff frequency requires L = 31.8 nH and C = 12.73 pF.

The filter is symmetric. This means that the attenuation does not change if the input and output are reversed.

💡 It’s important that the filter impedance match that of the source and load (usually 50 ohm and sometimes 75 ohm). In the event that there’s a mismatch, some of the power will be reflected back. Use this tool to calculate the forward and reflected power.

### Applications of Low Pass Filters

It is commonly used to remove or reduce high-frequency noise or signals. In power supplies a LPF will be used prevent high frequency signals from entering other parts of the circuit or the main supply.

## How to calculate the cutoff frequency of a CLC filter?

In some situations you might find an application note or chip data sheet that has a CLC filter design. To calculate the cut off frequency for the filter from the capacitor and inductor component values use the calculator below. Simply enter the L and C values and it will provide Fc.

fc= 1/(π*√(LC))

### Example Calculation

For L = 1 uH and C = 1 uF, the cutoff frequency is 318 kHz.

## Related Posts

• Pi Filter – includes four different calculators for both low pass and hi pass filters
• Power supply pi filters – for both equal and unequal impedance
• Filter Bandwidth – compute the bandwidth and center frequency from the start and stop frequencies. Useful when you look at the data sheets for SAW filters that don’t provide this info up front.
• T Filter – use this when the input impedance is low
• Pi Filter Cutoff Frequency – Use the component values from a schematic to find the cutoff frequencies for both low and high pass filters