Notch Filter :-

• A Notch Filter is also known as a Band Stop filter or Band Reject Filter.

• These filters reject/attenuate signals in a specific frequency band called the stop band frequency range and pass the signals above and below this band.

• For example, if a Notch Filter has a stop band frequency from 1500 MHz to 1550 MHz, it will pass all signals from DC to 1500 MHz and above 1550 MHz. It will only block those signals from 1500 MHz to 1550 MHz.

• Another example, in a musical instrument amplifier, a notch filter may reduce the frequencies within the range of 59 to 61 Hz, which is sufficient to eliminate any hum coming from the 60 Hz power line. See bandstop filter.

Working of notch filter :-

A notch-filter has the same working principle as of band-reject filter. It allows all other frequency components of the signal and blocks the specified narrow bandwidth. For a passive design, the resistive, capacitive and inductive reactance play the part of controlling the frequency.

Several applications of Notch-Filters are :-

• Communication Systems: Notch-Filters is one of the important pieces of equipment for a communication system. There is a high probability that the message signals get interfered with by harmonic noises in long-term communication. Notch-filters eliminate the noise.

• Audio Engineering: One of the basic components of audio engineering is a notch-filter. Eliminating noise, spikes are some of the tasks performed by a notch-filter.

• Medical Engineering: Notch-filters have been used in Medical Engineering. Reading of EEG is impossible without a notch-filter.

• Digital Signal Processing: Notch-filters have applications in Digital Signal Processing. A notch-filter is important when there is a need for mixing up signal or condition of elimination of certain frequency component.

• Digital Image Processing: Notch-filters help to eliminate noises from digital images.

• Optical Applications: Notch-filters have applications in optical applications. Blocking off a certain wavelength of light is done by specific optical notch-filters.