What is a filter used for and What are the types of filters

What is a filter used for and what does it do

Electric utilities are always concerned about the power factor or power quality. Power quality problems may arise due to the variation in voltage, current or frequency and this may lead to the equipment failure or malfunction. The use of electrical power has been increased a lot by the last decade. So the need for electric power increased and because of that, the power quality is an important factor. Due to the excessive need for electric power, there was a quick increase in non-linear loads such as domestic appliances, adjustable speed drives, etc. So in order to reduce these problems filters can be used, filters are circuits that can perform signal processing functions. Filters can remove unwanted frequency components from the signal to get a proper signal. Filters can change the amplitude and phase characteristics of a signal with respect to frequency. Filters won’t add new frequencies to the input signal, filters are used in many electronic systems.

What are the types of filters

A filter is a reactive network that freely passes the desired bands of frequencies while it suppresses all the other bands. Filters are constructed from reactive elements if not so, the attenuation would never become zero in the passband of the filter network. Filters do not produce any attenuation to the passband, which is called a transmission band or passband. It should provide attenuation to all the other frequencies, called attenuation band or stopband. Filter networks are widely used in communication systems to separate various voice channels in carrier frequencies telephone circuits. The filter also has applications in instrumentation, telemetering equipment, etc. A filter may have a number of passbands separated by attenuation bands and they are classified into four types they are low pass, high pass, bandpass, and band-reject filter.

Low pass filter

This type of filter resistor and capacitor is used for its construction and this circuit can remove unwanted high frequencies from electrical signal and it will only pass the required signal. A passive low pass filter can be easily created by connecting together in a series single resistor with a single capacitor. In this circuit, the input signal is applied to the series combination but the output signal is only taken across the capacitor. It is also called the first-order filter because it has only one reactive component which is the capacitor. Active low pass filter, its operation, and principle are the same as the passive filter, but an op-amp is used for the amplification and gain control.

High pass filter

A high pass filter will only pass high-frequency signals and it will block or impedes low-frequency signals. A high pass RC filter will only pass high-frequency signals and its circuit is composed of a resistor and a capacitor. To create this circuit capacitor is placed in series with the power signal that enters the circuit. The capacitor provides high resistance to low frequency or DC signals, and it will provide low resistance to high-frequency signals. The operation of active high pass filter is the same as the passive high pass filter except the active high pass filter uses an op-amp in it.




Bandpass filter

This type of filter will only allow the frequencies which are predefined to pass through it will remove all the frequencies which are above and below the set values. It is a combination of high pass and low pass filter. A bandpass filter can be obtained by cascading both high and low pass filters. This filter will only allow a certain range of frequency, bandpass filters have many applications, they are used in audio amplifier circuits and wireless transceivers, etc.

Band reject filter

This filter is also known as a band stop filter which passes most of the frequencies unaltered, but it will attenuate those in a specific range to very low levels. It is the opposite of the bandpass filter. Bandstop filter blocks and rejects frequencies that lie between its two cut-off frequency points pass all those frequencies either side of this range. It can be constructed by the combination of low and high pass filters.


post-graduate in Electronics & communication.

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