How to Design a High-Pass Filter Circuit

In this post we learn how to design a high-pass filter circuit within minutes by following similar procedures quite similar to ones suggested in our previous post for the low pass filter.

What is High Pass Filter

As the name suggests a high-pass filter circuit is designed to attenuate all frequencies below a particular selected frequency, and pass or allow all frequencies above this threshold. The principle is just opposite to a low-pass filter circuit.

The cut-off range is generally at a relatively higher frequency range (in kHz),

The following high pass filter response graph shows the waveform image indicating how all frequencies below a selected cut-off threshold are attenuated or blocked gradually, as frequency decreases.

The following two images are configured as standard high-pass filter circuits, where the first one is designed to work with a dual supply whereas the second one is specified to operate with a single supply.

In both the above configurations, the opamp forms the central processing active component, while the associated resistors and capacitors wired across the input pins of the opamp are introduced for determining the high-pass filter cut-off point, depending upon how the values of these passive components are calculated as per the users specifications or requirements.

How to Design a Customized High Pass Filter

As proposed, to design a high-pass filter circuit quickly, the following formulas and the subsequent steps can be used for calculating the relevant resistors and capacitors.

First, select an appropriate value arbitrarily for C1 or C2, both can be identical.

Next, calculate R1 by using the following formula:

R1 = 1 / √2 x π x C1 x Frequency

Here the term "frequency" refers to the desired high-pass cut-off threshold below which other unwanted frequencies need to be attenuated or ignored gradually.

Finally, calculate R2 in the same way as above using the following equation:

R2 = 1 / 2 √2 x π x C1 x Frequency

The single supply version of the high pass filter circuit can be seen involving another capacitor Cout which is not at all critical and can be approximately 100 or 1000 times more than C1.

The above discussions shows how simply anybody can calculate and design a high-pass filter circuit quickly for a particular application which could be a treble control circuit, a 10 band graphic equalizer or a home theater circuit etc.