# WHAT IS A FREQUENCY FILTER AND WHAT TYPES ARE THERE?

## What is a frequency filter?

A frequency filter is a circuit that uses electrical and / or electronic components to attenuate, correct, or reject a range of frequencies within any type of signal. This range can be different each time since the filters are very flexible and there are different types.

## What is the frequency?

There are several parts of an electrical signal that can change their values ​​over time or each time a new signal is generated. The frequency is one of these values ​​and practically the most important to know the operation of the filters.

All signals have a pattern that repeats over time, this pattern is known as frequency , this value is measured in Hz / s, that is, how many repetitions are there in one second. For example, if we have a 1Hz / s signal, it means that the signal repeats 1 time per second, but if we had a 1,000 Hz / s signal, it means that the signal repeats a thousand times in one second.

## Filter classification

A popular way of classifying frequency filters is based on the type of electrical and electronic components used, since we can create the same type of filter with different components.

### Passive filters

These filters use basic electrical components such as resistors , capacitors and coils , because they are quite simple and have some disadvantages. They are difficult to adjust and have low power.

Within the passive filters we can find some variations that are; those of a single element, those of multiple elements, those of type T, π and L. (Article to be treated)

### Active filters

The assets also use three basic components, but more complex components added as are operational amplifiers . Thanks to this incorporation, these types of filters are easier to adjust and can have a signal amplification, to obtain greater power.

## Filter types by frequency

The function of these filters is based on creating one or more cutoff frequencies to pass part of the signals that are above, below or between the cutoff range, it all depends on what type of filter is being used. It should be mentioned that there are different types of circuits for each of the filters

### Pass low

As its name implies, this filter allows frequencies that are lower than the cutoff frequency to pass, depending on the complexity of the filter, it can attenuate signal changes that are above the cutoff frequency or can also eliminate them

For example: a filter with passive components can only attenuate the signals, however a digital filter with all the processing it performs is capable of eliminating them.

### High pass

It is practically the same case as the previous filter, except that this works in reverse, that is, it allows frequencies above the cut zone to pass and those below it eliminate or attenuate them as appropriate.

### Pass band

This filter is practically the fusion of the two previous filters since it is required to establish two cutoff frequencies, a high one to eliminate those that are above and a low one to eliminate those that are below, that is, this filter lets freely the frequencies that are within the cutoff ranges.

### Reject band

These filters also need two cut-off frequencies, a low and a high , but they work completely opposite to the bandpass since, as the name implies, they reject the frequencies that are within the cut-off range.