Download research about filters

research about filters
IBRAHIM ABDELATY
SHOSHA
[DATE]
SHA
Introduction to Filters
A frequency filter or also known as a frequency selective circuit
is a special type of a circuit, which is used for filtering out some
of the input signals based on their frequencies.
A filter circuit passes some frequency signals without any
attenuation (Reduction in amplitude) or with some amplification,
& attenuate other frequency depending on the types of the filter.
What Is a Filter?
The Electronic Filter is an electrical or electronic circuit which
allows to the passing of the signals of a predetermined
frequency and rejects all other frequency signals.
We know that any electronic signals have some frequency. Most
of the cases we used only the signal having a particular
frequency.
In the signal transmission purpose, we send and receive highfrequency signals to get better bandwidth and to send or receive
a large amount of data. But after receiving the signals we have
required to filter those signals to get the signal of a particular
required frequency.
For example, we received a signal of 20MHz, but we need up to
the 10MHz signal. So, in this case, we use a filter circuit which
allows up to 10 MHz signals and rejects beyond the 10MHz
signals.
Types of Electronic Filter:
According to the circuit element types, the electronic filter
classified into two types,
1-Active Filter
2-Passive Filter
Active Filter:
The filter circuit which is made by active elements
like Transistors, Op amp, diodes etc. is called Active Filter.
Types of Active Filter:
According to signal filtering characteristics, the Active Filter is
classified into four types,
1-Active Low Pass Filter
2-Active High Pass Filter
3-Active Band Pass Filter
4-Active Band Reject Filter
Passive Filter:
The filter circuit, which is made by passive elements like
resistors, capacitors, inductors is called Passive Filter.
Types of Passive Filter:
1-Passive Low Pass Filter
2-Passive High Pass Filter
3-Passive Band Pass Filter
4-Passive Band Reject Filter
So, from the above concept, we can say there are four types of
Electronic Filter which are,
1-Low Pass Filter
2-High Pass Filter
3-Band Pass Filter
4-Band Reject Filter
These above filters can be designed either taking active
elements or passive elements. These basic four types of filters
we will discuss.
Low Pass Filter:
The filter circuit which allows passing the signals having the
low frequency (starting from 0 to predetermined cut-off
frequency) and rejects the signal having the frequency beyond
that cut-off frequency is called Low Pass Filter.
For example, a 50MHz signal is present but we need the signal
up to 25MHz. In this case, we have needed a low pass filter
which will allow the passing of the signal having the frequency
from zero (0) to 25MHz and will reject the signal having the
frequency beyond 25 MHz.
Examples of Low Pass Filter:
1-RC Low Pass Filter: This is the filter circuit which is designed
by resistor and capacitor.
2-RL Low Pass Filter: This is the filter circuit which is designed
by Resistor and inductor.
2-RLC Low Pass Filter: This is the filter circuit which is designed
by resistor, capacitor, and inductor.
To better understand the working of low pass filter let's discuss
RC Low pass filter, To better understand the working of low
pass filter let's discuss RC Low pass filter,
RC low pass filter circuit diagram
As you see in the above figure, the circuit has a capacitor is
connected in parallel. The working of this circuit is very simple.
According to the below equation, we know that the reactance of
the capacitor is inversely proportional to the frequency.
So, when a low-frequency signal is passing through the circuit
the reactance of the capacitor will be high and we will get the
output signal same as the input signal. But when a highfrequency signal is passing through the circuit the reactance of
the capacitor will be low so the current(electronic signal is a
flow of current) will flow through the capacitor or we can say
the capacitor complete the circuit so we will not get any output.
You can also understand the principle by the below equation,
Applications of Low Pass Filter:
1.
Low Pass Filter used in Digital Signal Processing
2.
It used in Audio Equalization purpose.
3.
It is used to reduce high-frequency noise in Audio.
4.
It is used as anti-aliasing filters in Analog to Digital
Conversion.
High Pass Filter:
The filter circuit which allows passing the signals having the
high frequency starting from a predetermined cut-off frequency
and rejects the signals having the frequency below that cut-off
frequency is called High Pass Filter.
Suppose we have signals of 50MHz, but we need the signal
beyond 25MHz. In this case, we have needed a High Pass Filter
which will reject the signals having the frequency below 25MHz
and allow the beyond 25MHz signals.
Frequency Spectrum of High Pass Filter is shown below,
Examples of High Pass Filter:
1.
RC High Pass Filter
2.
RL High Pass Filter
3.
RLC High Pass Filter
To better understand the working of the high pass filter let's
discuss the RC high pass filter,
RC high pass filter circuit diagram
As you see in the above figure a capacitor is connected in series.
So, when a high-frequency signal is flowing through the circuit,
the reactance of the capacitor will be low and we will get the
output signal but when the input signal has low frequency the
reactance of the capacitor will be high and as it is connected in
series it will oppose the flow of the current and we will not get
output.
Applications of High Pass Filter:
1.
2.
High pass filter is used in digital image processing.
It used to reduce low-frequency noise
3.
It is used as the treble booster circuit in the audio
system.
Band Pass Filter:
The filter circuit which allows passing the signals having the
frequency which is under a certain band and rejects the signals
having the frequency which is outside of that band is called
Band Pass Filter.
We have signals of 60mhz but we need the signals of 20-30mhz.
So we have needed a band pass filter which will pass the 2030mhz signals and will reject below the 20mhz and beyond the
30mhz signals.
Frequency Spectrum of Band Pass Filter is shown below,
Examples of Band Pass Filter:
1.
RC Band Pass Filter
2.
RL Band Pass Filter
3.
RLC Band Pass Filter
We can easily make a Band Pass filter using an RC low pass
filter and an RC high pass filter.
RC Band pass filter circuit diagram
As you see in the above figure the circuit has a series capacitor
and a parallel capacitor. The series capacitor can reject the lowfrequency signal and the parallel capacitor can reject the highfrequency signal. By choosing the appropriate value of the
capacitors we can make a frequency band at which the signals
can pass through the circuit.
Applications of band Pass Filter:
1.
In the telephone system, Band Pass filters are used.
2.
It is used in SONAR system
3.
It is used in Audio Technology
Band Reject Filter:
The filter circuit which rejects the signals having the frequency
which is under a certain band and allows passing the signals
having the frequency which is outside of that band is called
Band Reject Filter.
We have signals of 100MHz but we need the signal of 0-30MHz
and 60-100MHz. So we need a Band Reject filter which will
reject the signals having the frequency of the band 31-59MHz
and will allow the signals having the frequency of outside of the
31-59MHz band.
Frequency Spectrum of Band Reject Filter is shown below,
Example of Band Reject Filter:
1.
RLC Band Reject Filter
We can use an RLC parallel circuit as a Band Reject filter. In
Parallel Resonance condition the circuit act as Band Reject filter
circuit. The output can be obtained across the resistor.
RLC Band reject filter circuit diagram
Applications of Band Reject Filter:
1.
In Telecommunication system, Band Reject Filters
are used.
Applications of Filters

Filter Circuits are used to eliminate background Noise
 They are used in Radio tuning to a specific frequency
 Used in Pre-amplification, Equalization, Tone Control in
Audio Systems
 They are also used in Signal Processing Circuits and Data
Conversion
 Filter Circuits are extensively used in Medical Electronic
Systems
Advantages of Filters

They are economical or cost-effective

Unlike passive filter circuits, Active Filter Circuits
require power supply
Disadvantages of Filters

Circuits are bulky

Limited Bandwidth

Increased sensitivity to variation in circuit parameters