What Types of Filters are Commonly Used?

Notch filters are used to attenuate a narrow range of frequencies. The four main types of filters include low-pass filter, high-pass filter, band-pass filter, and notch filter (or band-stop or band-stop filter). Electronic filters are mainly used to process electronic signals by eliminating unwanted frequency components or improving others. They generally operate at frequencies below RF (radio frequency).

Typical operating frequency ranges are AF (audio frequency) or IF (intermediate frequency), both of which are power frequencies. There are many types and functions for electronic filters, including passive or active, analog or digital, and low-pass and high-pass. Electronic filters are also used to minimize or eliminate electrical noise.

Ideal Filter Response

The various approaches to the ideal filter response are identified by names such as Butterworth, Chebyshev, Bessel and others.

Probably the most commonly used filter is the Butterworth, which has the characteristic amplitude response shown in the following figure. Butterworth filters have a planar maximum response in the passband; that is, passband flatness is the ideal emphasized filter characteristic, but it is achieved at the expense of phase linearity and attenuation slope. However, the attenuation slope of the Butterworth filter is quite good and, for applications where phase linearity is not important, the Butterworth response is an excellent general purpose approach to the ideal filter.

Active Filters

Active filters can be classified into a voltage-type active filter and a current-type active filter, depending on the energy storage components.

The voltage-type filter is widely used due to its low loss and high efficiency. Common-type filters are less used due to high losses and low efficiency. According to the AC and DC power supply, it can be divided into DC APF and AC APF. According to the circuit topology structure, it can be divided into APF series, APF parallel and series-parallel, and a hybrid use of APF and PPF.

Passband & Stopband

The frequency band of the input signal that passes through the filter without any attenuation is called the passband. In general, the passband has no gain considering that the filter is a passive filter. In active filters, the passband may have some gain depending on the circuit configuration. The frequency band of the input signal that are blocked or attenuated in the filter is called the stopband.

The gain at the stop is generally considered to be less than -3db from the input. Passband & (stopband) is distinguished from each other by cut-off frequency or corner frequency. The output signal voltage at the cut-off frequency is 70.7% of the input signal voltage. It is also known as the “-3db” frequency because -3db represents half the power.

Y is the frequency at which the power of the output signal becomes half the power of the input signal. The frequency that is in the center of the passband or stop band in a bandpass filter or band-reject filter, respectively, is called the center frequency. It is located between the two cut-off frequencies, that is,. In fact, it is the arithmetic mean of both cut-off frequencies.

The range of frequencies that are passed (in the case of the bandpass filter) without any attenuation or the frequencies that are attenuated (in the case of the band rejection filter) is called the filter bandwidth. The width of the frequencies before (in the case of the low-pass filter) or after (in the case of the high-pass filter) the cut-off frequency is called the bandwidth. Passband frequencies & are defined by the filter cut-off frequency. Any frequency lower than the cut-off frequency is passed without any attenuation.

While any other higher frequency signal, the cut-off frequency will be blocked. Any signal with a frequency lower than the filter cut-off frequency is blocked. Whereas any signal with a frequency higher than the cut-off frequency passes full amplitude.

Bandpass Filters

This type of filter allows a specific frequency band & to block any other frequency lower or higher than its passband frequencies.

This type of filter has two cut-off frequencies, i.e. Bandpass blocks low frequencies & high frequencies, while allowing intermediate frequencies known as passband frequencies. Any input signal having a frequency that belongs to the passband frequencies will pass without any attenuation.

Signal Processing Filters

In signal processing, a filter is a device or process that removes some unwanted components or characteristics from a signal.

Filtering is a kind of signal processing, the defining characteristic of filters being the complete or partial suppression of some aspect of the signal. In most cases, this means eliminating some frequencies or frequency bands. However, filters do not operate exclusively in the frequency domain; especially in the field of image processing, there are many other objectives for filtering. Correlations can be eliminated for certain frequency components and not for others without having to act in the frequency domain.

Filters are widely used in electronics and telecommunications, radio, television, audio recording, radar, control systems, music synthesis, image processing and computer graphics. A low-pass filter is a filter that allows signals with a frequency lower than a particular cut-off frequency to pass through it and depresses all signals with frequencies beyond the cut-off frequency. Air filters are systems or components that remove particles from the air as it passes through the filter elements and can be complete systems or replacement elements on their own. Fuel filters are primarily used to filter debris or unwanted substances from fuel to protect equipment and allow fuel to burn more efficiently.

Water filters are primarily used in any system that requires water to be filtered or cleaned to remove debris and particles. The analog Bezier filter is...