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Types of Filters – A Comprehensive Guide

Generally, filters are processes or devices that get rid of unnecessary features/components from a frequency signal during signal processing. They’re common in computer graphics, image processing, control systems, radars, telecommunication, etc. What’s more, there are various types of filters which we’ll learn about today.

What Is a Filter?

A filter is a circuit that removes unwanted components like electronic signals, dirt, etc., as they’re passing through filtering devices/media. 

Another definition majors on attenuating specific frequencies while amplifying or allowing the passage of others frequencies. Thus, electronic filters retrieve frequencies from signals with irrelevant or unrequired frequencies. 

Types Of Filters

Manufacturers classify several filters depending on their construction method and frequency method.

Based On Their Construction

Two filter types fall under the construction feature. 

  • Passive Filters

A passive filter is a type of filter that has passive components, including inductors, capacitors, and resistors. 

Then, since they require no external energy source, the filters won’t have a voltage gain. That also means you’ll always receive a lesser output voltage than the input voltage. 

In addition, despite not processing low frequencies, passive filters can filter high-frequency signals easily. 

Lastly, passive filters have simple designs. However, once you connect a load to the filter, you’ll affect its characteristics. Also, you can impact its elements by cascading the filter for a higher-order filter. 

  • Active Filter

Contrary to passive filters, active filters have active components like transistors, operational amplifiers, capacitors, and resistors. 

Unfortunately, it works with an external power source, although it’ll generate a high voltage gain. The voltage gain further amplifies weak input signals. Also, it won’t process extremely high-frequency signals, but it will filter exceptionally low-frequency signals. 

Further on, active filters have a complex design but can provide low output and high input impedance. It explains why any load impedance won’t impact the filter’s characteristics. 

Finally, if you want to augment the filter’s order, use active filters in cascading configurations. You won’t have to worry about losing the input signal power. 

Based On Their Frequency Response

The second classification of filters depends on the types below; 

Low Pass Filter

A low pass filter permits signals with low frequency without decreasing their power but rejects high-frequency signals. 

The filter comprises a reactive component that causes variation with the input frequency. Thus, the reactance variation causes a circuit decrease or increase in voltage drop. Then, a large voltage drop at the output will allow the signal to pass. If the drop is lower, the filter will block the signal. 

High Pass Filter

A high pass filter rejects/blocks a low-frequency signal while allowing the passage of high-frequency signals without attenuating their amplitude. 

A higher frequency signal (compared to cut-off frequency) can pass with a complete amplitude. Conversely, the filter blocks a lower frequency signal than the cut-off frequency.  

Band Pass Filter

The filter blocks frequencies higher or lower than the passband frequencies but permits a particular band of frequencies. 

Furthermore, it consists of two cutoff frequencies, upper and lower cutoff frequency. Therefore, the filter will block high and low frequencies while allowing the passband frequencies (in-between frequencies) without any attenuation. 

If you combine a high pass filter and a low pass filter in a cascade configuration, you’ll get a bandpass filter. The high pass filter will block low frequencies, while the low pass filter will block high frequencies.

Band Reject Filter/Notch Filter/Band Stop Filter 

A band-reject filter reduces or limits the signal frequencies in a fixed band of frequencies. 

Its operation is the complete opposite of a bandpass filter. A notch filter permits high-frequency and low-frequency signals but limits the fixed band of frequencies between signals. 

Moreover, it has upper and lower cut-off frequencies. However, if the cut-off frequencies receive any signal frequencies in between them, the filter rejects the signals. 

Response Curves

Generally, response curves display how a filter behaves. An example includes the diagram below with a variety of filters. 

Applications of Filters

Often, you’ll get filters applied in the following areas;

TV

(TV)

Automotive manufacturing

(Automotive manufacturing)

Conclusion

In summary, you can apply filters in projects that require undisrupted signals. Furthermore, the various filters act as the guide to specific device usage. 

If you have any questions concerning frequency filters, don’t hesitate to reach out to us

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Hommer Zhao
Hi, I am Hommer, the founder of WellPCB. So far, we have more than 4,000 customers worldwide. If you have any questions, you can feel free to contact me. I really appreciate any help you can provide.

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