Band Pass Filter
Band Pass Filter
A system called a band pass filter or BPF is needed during signal processing to allow a specific range of required frequencies and to prevent unnecessary frequency ranges or components. This filtering noise signal can be minimised by deleting frequencies that are not necessary. Various types of filters, such as linear and nonlinear, optical, active and passive etc., are eligible for use on a requirement basis.
What is Band Pass Filter?
Band pass filter is an electronic circuit or system that allows only signals between certain frequencies to pass through and attenuates/rejects frequencies outside the range. Band pass filters are commonly used in wireless receivers and transmitters, but are still widely used in many fields of electronics.
Band pass filters are easy to design and build, and only minimal components are needed. The most important parameters for a band-pass filters are:
- High cut-off frequency
- Low cut-off frequency
- Bandwidth
- Center frequency
- Center frequency gain
- Selectivity
There are two cut-off frequencies in this bandpass filter, one of which is a high pass filter and its high cut-off frequency. This would be the band's peak frequency cap. There is another cut-off frequency from the low-pass filter, and the second cut-off frequency is defined as the lower cut-off frequency that defines the low-frequency spectrum of that band.
The cascading or combination of a high-pass filter and a low-pass filter produces a bandpass filter that allows for a certain frequency band and attenuates signals that are higher and lower than the cut-off frequency. This bandpass filter would make input signals without interference or noise. The range of this frequency band is called the bandwidth. To specifically describe bandwidth, it is the unique frequency spectrum that lies between the two cut-off ranges, i.e. the high cut-off frequency range
Bw= fH – fL
The difference between the lowest cut-off frequency and the highest cut-off frequency is known as bandwidth.
As an optimal bandpass filter, the filter must filter or attenuate those frequencies within the band to reduce noise. Bandpass filters are also known as second-order filters due to the fact that there are two capacitors, reactive components within a single circuit. One capacitor in the high-pass circuit and another capacitor in the low-pass circuit.
Various types of bandpass Filter
These bandpass filters are mainly categorized into two types of filters. They are
- Wide Band Pass Filter
- Narrow Band Pass Filter
Narrow band pass filters have quality factor selectivity Q greater than 10, and small band pass filters have quality factor selectivity Q less than 10. Some band pass filters might need an external source of power and use active components like integrated circuits and transistors; these are known as active band pass filters. Some band pass filters do not need any external source of power and use mainly passive components like inductors and capacitors; these are known as passive band pass filters. Compared to passive band pass filters, active band pass filters have more effective performance. A band pass filter is capable of optimizing the signal-to-noise ratio and improving receiver sensitivity. Band pass filters are used in RF applications where tuned circuits are needed. They are used in transmitters to limit the bandwidth of the output signal, so that the signals are only transmitted in the band allocated for the transmission and thus do not interfere with other stations. Band pass filters in receivers help to allow signals within the selected frequency range to get through and block signals of unwanted frequencies. Band pass filters are also used in other fields such as atmospheric sciences, neuroscience and astronomy. Optical band pass filters are used in astronomy, spectroscopy, imaging, clinical chemistry and microscopy.
Bandpass Filter Calculator Calculation
This is the passive bandpass filter circuit and the bandpass calculations can be done through this circuit.
BPF Calculation
By using the formula we can find out the required frequency in this passive bandpass filter.
For high cut off frequency = 1/2ΠR1C1
For low cut off frequency = 1/2ΠR2C2
Even we can also calculate required frequencies for the different bandpass filters like active inverting op-amp BPF and active non inverting op-amp BPF
Band Pass Filter Applications
The applications of bandpass filters include the following.
- These filters are extensively applicable to wireless transmitters & receivers.
- This filter can be used to optimize the S/N ratio (signal-to-noise) as well as the compassion of a receiver.
- The main purpose of the filter in the transmitter is to limit the BW of the output signal to the selected band for the communication.
- BPFs are also widely used in optics such as LIDARS, lasers, etc.
- The best application of this filter is audio signal processing, wherever a specific range of sound frequencies is necessary though removing the rest.
- These filters are applicable in sonar, instruments, medical, and Seismology applications.
- These filters involve communication systems for choosing a particular signal from a variety of signals.
Band Pass Filter Circuit