High Pass Filter Circuit

In this article, we will show how to build a high pass filter.

This is a filter that passes through high frequency signals without any attenuation and blocks low frequency signals from passing through. Low frequency signals will either be completely blocked or greatly attenuated as output.

To build a high pass filter, we will be using the following components:

Components

A function generator (or any device that can produce AC signals)
0.1µF ceramic capacitor
10KΩ Resistor

This is the schematic of the circuit we will build, shown below:

We input an AC signal into the circuit from any source. The most common source would be from a function generator. If you place the signal to a very low frequency signal such as 0.1Hz (100 mHz), the capacitor will block out this voltage signal and it will not go through to output. If you now increase the frequency of the signal to 1KHz, the signal will will go through unimpeded, not being blocked at all. The capacitor will have no effect and all high frequency signals pass through completely unimpeded without any attenuation.

This is a diagram below showing what happens to low and high frequencies when fed into this high pass filter:

The low frequency signals (near 0 Hz) are blocked and do not go past the capacitor. Therefore, these signals do not show up on output. The high frequency signals go through unimpeded and pass to output. This is why it's a high pass filter. It passes through high frequencies but block low frequencies.

Note that this low pass filter only blocks very low frequencies. The frequency of the signal has to be very close to 0Hz for the capacitor to have effect (for there to be capacitive effect). This means that the frequency should only be a few millihertz, at most 1Hz. Anything above 1Hz and the capacitor blocks less and less of the signal. Even at 4Hz, there is no capacitive effect, so a 4Hz signal will not be blocked at all but passes through unimpeded and unattenuated. This high pass filter only blocks very low frequencies, near 0Hz.