بسم هللا الرحمن الرحيم
Palestine Polytechnic University
College of Information Technology and Computer
Engineering
passive band pass filter
Dr. zaher saafin
Student name Student number
Nour Turman 211092
Samah Mebed 201012
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Objectives:
After performing this experiment, you will be able to:
1.Gain a comprehensive understanding of the characteristics of passive
band pass filter and how passive band pass filter is working.
2.Learn to design and implement passive band pass filter circuits using
RLC circuit.
Materials Needed:
1.Two Capacitor.
2.Two Resistance
3.AC voltage or Function generator
4. Oscilloscope
5.Bode Plotter
Theory:
A Bandpass filter is a circuit or device designed to selectively permit a
specific range of frequencies to pass through while attenuating those
below and above the predetermined values. It combines the
characteristics of a high-pass filter, allowing frequencies above a set
value, and a low-pass filter, allowing frequencies below a set value.
Essentially, a bandpass filter allows only a defined band of frequencies to
pass through.
In its composition, a high-pass filter permits frequencies higher than a
specified point, while a low-pass filter allows frequencies lower than a set
value. By cascading these two filters, a bandpass filter is created. This
type of filter finds extensive applications in audio amplifier circuits and
wireless transceivers where it is essential for the speaker to reproduce
only a specific range of frequencies, disregarding others.
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Bandpass filters are categorized into two types. An Active Bandpass filter
involves external power sources such as transistors, while a Passive
Bandpass filter consists solely of passive components like resistors,
capacitors, and inductors without any active devices. This discussion will
focus on Passive Bandpass filters. Additionally, this article will touch
upon other classifications and aspects relevant to these filters.
In the context of a passive filter, such as an RC (resistor-capacitor) filter,
the cut-off frequency that often denoted as(Fc) is a critical parameter that
delineates the boundary between the frequencies that are attenuated and
those that are allowed to pass through.
The cut-off frequency is a key parameter in filter design and determines
the range of frequencies that the filter is designed to either pass or
attenuate. It is calculated using specific formulas based on the values of
the resistor (R) and capacitor (C) in the filter circuit. The precise formula
varies depending on the type of filter (low-pass, high-pass, band-pass,
etc.) and the desired characteristics of the filter's frequency response.
FIG1.1
As previously mentioned, our focus now shifts to the Passive Bandpass
Filter, which is assembled using resistors and capacitors. This filter
amalgamates the features of both high-pass and low-pass filters. Below is
an illustrative circuit diagram showcasing a basic passive Band pass
filter.
FIG2.1
The first half of the circuit is a High-Pass filter which filters the low
frequencies and allows only the frequency that is higher than the set high
cut-off frequency (FH). The value of this high cut-off frequency can be
calculated using the formulae
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FH = 1 / 2π*R1*C
The second half of the circuit is the Low-Pass filter circuit which filters
the higher frequencies and allows only the frequency that is lower than
the set low cut-off frequency (FL). The value of low cut-off frequency can
be calculated using the formulae
FL= 1 / 2π*R2*C2
FIG3.1
When an input signal frequency is applied to the filter, it yields an output
frequency higher than fcLOW and lower than fcHIGH. In simpler terms,
the output frequency is determined by the difference between fcHIGH
and fcLOW, and the range within this region is referred to as the
bandwidth. Consequently, the bandwidth of the filter can be computed as:
Bandwidth= FH – FL
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FIG4.1
Benefit and Applications of Bandpass Filters:
Bandpass filters operate by selectively allowing a specific range of
frequencies to pass through while blocking lower and higher frequencies.
They are constructed using both low-pass and high-pass filter networks.
Here are various applications and benefits of bandpass filters:
1. Wireless Communication:
- Bandpass filters are employed in both transmitter and receiver circuits
in wireless communication systems.
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- They enable the transmission of only relevant signals, reducing
unwanted noise and attenuation.
2. Signal-to-Noise Ratio Optimization:
- Bandpass filters contribute to optimizing the signal-to-noise ratio in
receiver systems.
- By allowing only a specific band of frequencies, they enhance the
quality of received signals.
3. Optical Communication:
- Used in optical communication applications such as LIDARs and
lasers.
- Bandpass filters play a crucial role in allowing specific optical
frequencies while blocking others.
4. Color Filtering Techniques:
- Bandpass filters find applications in color filtering techniques,
contributing to the isolation of desired colors.
5. Medical Instruments:
- In the medical field, bandpass filters are utilized in instruments like
EEG (Electroencephalogram) and Seismology applications.
- They assist in isolating and analyzing specific frequency components
in medical signals.
6. Telephonic Systems:
- Integrated into telephonic systems, especially in DSL (Digital
Subscriber Line) technology.
- Used to separate phone and broadband signals efficiently.
These diverse applications showcase the versatility of bandpass filters in
various technological domains, making them a crucial component for
signal processing and communication systems.
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FH = 1 / 2π*R1*C
FL= 1 / 2π*R2*C2
Bandwidth (Bw)= fH – fL
FCenter(FC)= √FH-FL
Vout=#of square above X-axis *voltage scale’
Vin Frequency Resistance(R1) Resistance(R2) Capacitor(C1) Capacitor(C2) Vout
1V 1 kH 10Kohm 10Kohm 15nF 560pF
7V 2 KH 1Kohm 5Kohm 15uF 45nF
12 V 500 HZ 800 ohm 10Kohm 100nF0 125uF
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