What is a Filter ? Describe The Classification of Filters

The process of removing unwanted frequencies is called attenuation. A band pass filter primarily attenuates high frequencies so that the resulting output is comprised of only frequencies within the passband. A passive band-reject filter can be designed with an LC circuit. The working of the LC filter is quite simple. Inductors come with a reactance as well as capacitors also come with capacitive reactance. Now an increase in the frequency causes the decrease in capacitive reactance and increase in inductive reactance.

Sallen key is another topology of designing filters. The bandstop filter can also be created using the topology. Sallen key topology is designed using operational amplifiers for creating higher-order filters.

To know more about the notch filter, check out my article on Notch filter. The main instruments for this filter are – capacitor and inductor. As the name suggests, the inductor and capacitor are kept in series. At resonance, the circuit can attenuate certain frequencies before reaching the load.

This is the primary principle behind LC bandstop filter. The bandstop filter can be designed in several ways. It can be active types (which has op-amp). It can be for passive kinds (without op-amp). Active types have several varieties, too as well as passive filters have different styles too.

Both filters rely on the concept of capacitive reactance in order to function. Hence, signal of any frequency beyond fc is faithfully reproduced with a constant gain, and frequencies from 0 to fc will be blocked. The ideal response of a low pass filter is shown in fig. The filter that performs exactly the opposite of the band-pass filter is the Band-reject filter. Q is given by the ratio between the resonant frequency to the bandwidth. It is an important parameter and it helps us to calculate the selectivity.

Narrow band stop filter

Such band-reject filters are known as RC band top Filter. The resistors and capacitors are connected in parallel which filter performs exactly the opposite to the band-pass filter at first; then, they are connected in series. The frequency components are trapped in between them.

• These types of designs don’t have a unity gain at zero frequency.
• Band Reject Filter can also be obtained by using the multiple -feedback bandpass filter with an adder.
• This filter consists of a high-pass filter, a low-pass filter, and a summing amplifier to summation the lpf and hpf’s o/p, The circuit is shown below.

That is why there are several circuits available also. In this article, almost all possible courses are given below. Before diving into a band-reject or bandpass details, let us understand what pass band and stop band means. A passband is the frequency bandwidth that is allowed by a filter.

An active Band Pass filter is used in the public addressing https://1investing.in/ system and speakers for enhancing the quality.

There are some different kinds of noises. At first, the frequency is matched with the noise frequency. Then the bandstop filter removes the noises and makes the image a better one. Low pass filters allow the lower frequency components of a filter and reject the higher frequency components.

How to design a Band Reject Filter?

The bandstop filter has several applications in Radio Frequency Domain. For example, during the measurement of non-linearities of a power amplifier. Also, when radio signals are transmitted from stations, band-reject filters are used to remove interfering noises. The bandstop filter is used in image processing.

According to the operating frequency range, the filters may be classified as audio frequency or radio frequency filters. BSF is used in radio signals to remove static on the radio devices for better and clear communications. At first, let us understand what the abode plot means. Abode plot refers to the graph of the frequency response of a device. Response of the band-reject filter is presented below. The frequency response of the filter in the stop band.

Audio bandstop filters, optical band-reject filters, digital-analog filters are some of its examples. Like high pass filters, low pass filters also feature a resistor and capacitor in series. However in the low pass filter, the output is taken across the resistor rather than the capacitor. This allows the circuit a high output when the capacitive reactance is high.

Bandwidth

Given the lower and higher cut-off frequency of a band-pass filter are 2.5kHz and 10kHz. This is also called as band elimination or notch filter. The frequency response of an ideal high pass filter is shown in fig.

A filter that provides a constant output from d.c. Upto a cutoff frequency fc and then passes no signal above that frequency is called an ideal low pass filter. A band stop or band reject filter always cuts or rejects frequencies that are not within a certain range, as the name implies. Besides this, it also gives easy passage to the frequencies to pass which are not in the range. These types of filters are often termed as ‘Band Elimination Filters’.

If the band of the frequency is narrow, the stopband filter is known as Notch Filter. In order for the band pass filter to function, the two filters must be cascaded together. The high pass filter attenuates frequencies above the passband, and the low pass filter attenuates frequencies below the passband. The voltage gain i.e. the ratio of output voltage to input voltage is constant over a frequency range from zero to cutoff frequency fc. Being a very important type of filter, bandstop filters has several applications.

Circuit diagram of band-stop filter

Active bandstop filters are designed using operational amplifiers. Op-amp is one of the most important devices in making a filter. In passive filters, as there is no op-amp, there is no amplification. Thus, using the op-amp as a circuit element gives amplification. A band pass filter removes frequencies above and below a designated band of frequencies called a passband. The band pass filter attenuates the frequencies around the band and outputs only the passband.

Resonant Frequency of Band Pass Filter

Let us find out some of the applications. The first stage of the band pass filter is the low pass filter. The first stage of the band pass filter is the high pass filter. Band pass filters are known as 2nd stage filters because they employ two sub-filter circuits, performing the total filtering ‘action’ in two stages. Optical band-reject filters block a certain wavelength of light and allow other components to pass. Just like normal band-reject filters, an optical filter rejects a certain wavelength.

Circuit using op-amp or the functional bandstop filter diagrams are given previously in this article. The band stop filter can be designed using basic components like resistor, capacitor, and inductor. There are two ways of developing the filter – 1. RLC parallel band-reject filter or Parallel resonant band-reject filter, & 2. As we are using passive elements, so both the filters will be of passive types. A notch filter is one type of bandstop filter.

Thus, we can understand this topology is for active filters. Unlike passive bandstop filters, active band-reject filters come with active components. The most important active part is the operational amplifier which also introduces amplification.