The main function of filters is to suppress or filter out components from mixed and unwanted frequency signals to ensure clear communication. In the **first article** of this series, we learned about the different types of filters, including low-pass filters which we covered in **the last tutorial**.

In this article, we’ll learn how to design a high-pass filter or HPF. These filters allow all of the frequencies that are higher than their cut-off frequency to pass while stopping all of the others.

**The first order of a high-pass filter**

**Step 1:**Select or choose the required cut-off frequency. For this tutorial, let’s suppose that we want to suppress all of the frequencies below 100 Hz. These frequencies are similar to a humming sound or power-line frequency noise (50 or 60 Hz). This means that: FC = 100 Hz**Step 2:**Now, assume the required value of the capacitor. It should be less than 0.1 micro Farad. This is required for better frequency stability. Let’s use the same value for C as 100 nF (nano farad)

*Steps 3 and 4 are shown here with the calculations required to find the resistance and pass-band gain for the first order of the high-pass filter.*

The final design with the component values is shown below. Since the op-amp is an active component, it requires +ve and -ve biasing voltages. It’s possible to test the circuit by applying input through the signal generator and observing the output on the DSO or the oscilloscope.

*A circuit diagram of the LM741 IC-based for the first order of a high-pass filter.*

**Note: **I have simulated the above circuit in

**NI’s multisim 11 software**. The schematic design is also prepared using the same software. The software is available as a free one-month trial period from National Instrument’s (

**NI**) website. The below circuits are also prepared using the multisim 11 software and tested in it.

**The second order of a high-pass filter**

**Step 1:**For simplicity, let’s assume that R1 = R2 = R and C1 = C2 = C**Step 2:**Select the desired cut-off frequency. For our purposes, let’s use FC = 500 Hz**Step 3:**Now assume the capacitor value of C as 100nF

*Steps four and five are shown here with the calculations required to find the resistance and pass-band gain for the second order of a high-pass filter. *

*A circuit diagram of the LM741 IC-based for the second order of a high-pass filter. *

**Higher-order high-pass filters
**Higher-order filters, such as the third, fourth, or fifth-order filters can be designed by cascading the first and second-order LPF sections. In this case, increasing the order increases the stop-band attenuation by 20 DB.

The figure below provides a clear image of this idea. By using the higher-order filter, we can get a better response with the stiff slop. For example, we may get a response such as an idle LPF.

*An overview of the third, fourth, and fifth order of a high-pass filter.*

The cut-off frequency for all the stages is the same, which means the RC value of all stages is also the same.

Filed Under: Tutorials

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