Active Filters

This filter passes all frequencies equally well, i.e., output and input voltages are equal in amplitude for all frequencies. The important feature of this filter is that it provides predictable phase shift for frequencies of different input signals. This filter allows a particular range of frequencies, which are above and below the cut-off frequencies of high pass and low pass filter circuits.

Band Stop Filter Calculator

The band stop filter allows frequency components below the cut-off frequency and above the cut-off frequency. The cut-off frequency of the low pass filter is denoted as fL and the cut-off frequency of the high pass filter is denoted as fH. As the band stop filter contains two cut-off frequencies for low and high-frequency ranges, it depends on the components used in the circuit. This article gives a complete description of the band stop filter.

It blocks the frequency components between the low and high-frequency ranges. When the input signal is applied, the high frequencies are passed through a high pass filter and low frequencies are passed through a low pass filter. The output voltage Vout drops at the high frequency of the high pass filter and at a low frequency of the low pass filter. These two filters are connected in parallel to allow all the high and low frequencies of a signal without any obstruction. The range of frequencies between the fL and fH is attenuated. An electric filter is a network designed to attenuate certain frequencies but pass others without attenuation.

• The ideal characteristics of the band-stop filter, which are opposite characteristics of band pass filter are shown below.
• Thus signal of any frequency beyond fc is faithfully reproduced with a constant gain, and frequencies from 0 to fc will be attenuated.
• This type of filter is mainly used to reduce the distortion in the signal.
• These spectral effects can be described as filters because one frequency region gets filtered out while the other region does not.

A high-pass filter (HPF) attenuates content below a cutoff which filter performs exactly the opposite to the band-pass filter frequency, allowing higher frequencies to pass through the filter. A low-pass filter (LPF) attenuates content above a cutoff frequency, allowing lower frequencies to pass through the filter. Consider the low-pass filter (LPF), sometimes also called the high-cut filter. In this effect, the low frequencies pass through the filter without being changed in amplitude. However, the high frequencies are reduced in amplitude; they are filtered out.

The band stop filter gives a wide frequency response when compared to the band pass filter. From the block diagram, we can observe that a band stop filter is a combination of a high pass filter and a low pass filter connected in parallel instead of series. The applied input signal is applied to the filter, the low pass filter allows only the low frequencies whereas the high pass filter allows the high frequencies of the signal. So, the bandstop filter will have two cut-off frequencies named as lower cut-off frequency and upper cut-off frequency. Upto a cutoff frequency fc and then passes no signal above that frequency is called an ideal low pass filter. The last two types of filters we will look at in this section are the notch filter and the band-pass filter (BPF).

In other words we can say that an electrical filter is usually a frequency selective network that passes a specified band of frequencies and blocks signals of frequencies outside this band. Many experimenters use an integrator to filter out high-frequency noise from their data, whereas a properly designed low-pass filter will remove more noise and distort the signal less. Viewed as a low-pass filter, the integrator is superior to the RC filter but inferior to higher order filters.

• This filter allows the frequencies of a signal in a particular range i.e., above and below the cut-off frequency.
• The low frequencies and high frequencies are reduced in amplitude, while a frequency band in the middle of the spectrum passes through without being changed.
• It is widely used to reject the specific frequency bands in reducing electrical noise, graphical equalizers, synthesizers, communications, biomedical applications, and many more.
• Consider the low-pass filter (LPF), sometimes also called the high-cut filter.

Notch Filter (Narrow Band stop filter)

The passband gain of this filter should be equal to the gain of the low pass and high pass filter. The bandwidth of the band pass filter is therefore, equal to fc2-fc1, where fc1 and fc2 are lower and higher cutoff frequencies respectively. The frequency response of an ideal band pass filter is shown in fig.

An electrical filter is a circuit which can be designed to modify, reshape or reject all the undesired frequencies of an electrical signal and  pass only the desired signals. Before embarking on the operational mechanism of the filter, let’s put light on the components of the filter. If you are designing a filter, either high pass filter (HPF) or low pass filter (LPF), you need electronic components such as a resistor, capacitor, amplifier etc. If we talk about high pass filter, so it is a circuit which allows the high frequency to pass through it while it will block low frequencies. On the contrary, low pass filter is an electronic circuit which allows the low frequency to pass through it and blocks the high-frequency signal.

In the notch filter, the low frequencies and the high frequencies pass though without being changed in amplitude. However, there is a notch in the middle of the spectrum where the amplitude is reduced. The low frequencies and high frequencies are reduced in amplitude, while a frequency band in the middle of the spectrum passes through without being changed. Depending on the type of elements used in their construction, filters may be passive or active. A passive filter is built with passive components such as resistors, capacitors and inductors. Active filters, on the other hand, make use of transistors or op-amps (providing voltage amplification, and signal isolation or buffering) in addition to resistors and capaci­tors.

The filter discussed above has ideal characteristics and a sharp cut-off but unfortu­nately, ideal filter response is not practical because linear networks cannot produce the discontinuities. However, it is possible to obtain a practical response that approximates the ideal response by using special design techniques, as well as precision component values and high-speed op-amps. These spectral effects can be described as filters because one frequency region gets filtered out while the other region does not. Consider the RC band stop filter to calculate the cut-off frequency. Hence, signal of any frequency beyond fc is faithfully reproduced with a constant gain, and frequencies from 0 to fc will be blocked. It is clearly observed that output voltage is non zero at low frequency and high frequency.

Band Stop Filters Question 3 Detailed Solution

Another type is the high-pass filter (HPF), or the low-cut filter. As the name suggests, the high frequencies pass through unchanged, while the low frequencies are attenuated. Therefore, this effect conceptually performs the opposite of the LPF. In practice, the switching mechanism of the capacitor changes the output characteristics of high pass and low pass filters and are not similar to the ideal filter.

The band stop filter with a narrow frequency response is known as a notch filter. It is designed to reject or block a particular band of frequencies and increases the selectivity of the filter. The quality factor ‘Q’ is very high when compared to the bandpass filter.

Basic Filter Effects

It allows all the frequencies below and above the cut-off frequency of low pass and high pass filter circuit. Since this circuit is designed using low pass and high pass filter circuits. This type of filter is mainly used to reduce the distortion in the signal. The band stop filter is a type of frequency selective circuit, that works exactly opposite to the bandpass filter. The name itself shows that it stops or rejects the particular range of frequencies of a signal. This filter is designed with the low pass filter and high pass filter, which are connected in parallel to allow high and low-frequency components.

The Frequency response of a practical low pass filter, when it works as an Integrator is as shown below. Depending on the type of techniques used in the process of analog signals the filters may be analog or digital. Analog filters are designed to process analog signal using analog tech­niques, while digital filters process analog signals using digital techniques. The frequency response of an ideal high pass filter is shown in fig. Below shows the frequency responses of the four  types of filters mentioned above. These are ideal responses and can not be achieved in actual practice.

The filter is sometimes called a high-cut filter, or treble-cut filter in audio applications. The band stop filter theory can be understood by using the block diagram shown below. The frequencies between fL and fH are attenuated, which represents the stopband.

Introduction to Filters

Figure shows the frequency re­sponses of the five types (mentioned above) of filters. These are ideal responses and cannot be achieved in,actual practice. There are many different types of spectral effects used in audio. These effects are typically used to change the amplitude of one frequency region in the spectrum by a different amount than another frequency region. The frequencies between 0 and fc , are called passband frequencies, while the frequencies above fc are called as stopband frequencies.