Notch Filters are another type of frequency selective circuit that is designed to block the transmission of frequencies within a particular frequency range and it permits frequencies outside that range. A notch filter is also known as a bandstop filter. This Is actually the inverse of the bandpass filter, which offers high-in-band transformation and high out-of-band rejection.
Notch Filters are useful in applications where laser light has to be blocked. For example, to get the right amount of noise in Raman Spectroscopy experiments. They also have wide usage in laser-based fluorescence instrumentation and biomedical laser systems.
Notch Filter Circuit Formation:
The notch filter is the combination of a highpass filter and a lowpass filter. It has a similar design as a bandpass filter. The only difference is that we connect both filters in a parallel manner instead of dropping down the connection.
The superior part of the notch filter circuit is passive RC low pass filter. The lower portion of the notch filter circuit is an RC high-pass filter.
Types of Notch Filter:
Notch Filter has many types, some most useful types are as follows:
Active Notch Filter:
The active notch is the parallel combination of highpass and lowpass filters with an amplifying component op-amp. The circuit diagram of the active notch filter has three parts.
- Active Low Pass Filter
- Active High Pass Filter
- The third part is an amplifier
The active low pass filter is parallel to the active high pass filter.
Passive Notch Filter:
The passive notch is the combination of passive low -pass filter and passive -high pass filter. The passive notch filter works only with small or passive components like inductors, resistors, and capacitors.
In-circuit diagram passive low pass filter is parallel with passive high pass filter.
Butterworth Notch Filter:
This is the special type of signal processing filter; the purpose of the Butterworth notch filter is to attain maximum flat frequency response. The Butterworth notch filter is ideal to get more accuracy than the ordinary notch filter. Because ordinary notch filter has a low signal-to-noise ratio.
Optical Notch Filter:
Optical notch filter blocks a selective portion of the spectrum while transmitting all other wavelengths. In optical density, it can be designed for various rejection levels.
An optical notch filter is mainly used in laser-based Raman spectroscopy, biomedical, and life science applications.
RF Notch Filter:
A narrow notch filter called RF notch Filter. It rejects carrier frequency during the measurement of non-linearities of power amplifiers.
Applications of Notch Filter:
Notch filters are used in high-quality audio applications like graphic equalizer and PA System. These filters have wide usage in image and signal processing to remove noise. These filters are used in biomedical applications like ECG for removing unwanted lines.
Notch filters have wide usage in optical communication technologies. The best example of notch filters in optical commination technology is Raman Spectroscopy. They are widely used in electronics and communications circuits to block unwanted frequencies.
Notch filters are used in telephone technology, DSL, and other internet services as line noise.
