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Lab
overview

This lab
experiment is performed to find out the central frequency of the band pass filter. The central frequency was
found with the help of circuit diagram and from the data table formed from the
observations. In this lab experiment, a stack of low and high band pass
filters was also prepared. During
the experiment, a pair of polarized capacitors was
used. These pair of
polarized capacitors with resistors was used to control the cut off frequency. These capacitors were added in a particular way to increase their capacity because the capacity of the capacitors depends upon the way in which
they are connected. In this experiment,
the bandpass filter is formed with the help
of low pass filters and high pass filters that were connected opposite to
each other, so that the bandpass
filter could pass the signals that have both low and high-frequency ranges collectively. A bandpass
filter could pass the signals with certain band or frequency without distorting
any of the input signals or without
producing any noise.

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The band of the various frequencies can
be having any width, and this width is called bandwidth of the filter.

The
cascading process can form the bandpass filter. Under this process,
cascading of high and low pass filter is performed. Cascading of low and
high pass filter means using the output of the first filter as the input of the second filter.

The bandpass filter can be used to isolate the frequencies that lie within a particular band or group of
frequencies. Each section of the filter resembles the frequencies of the previous filter. The
high and low pass filters have their resistors and capacitors that interchange
to form the bandpass filter.

The various
applications in which bandpass
filter is used have filter’ bands
and frequencies of a wider range made of mixed signals. The circuit that is used in filtering the frequencies is
designed by combining the properties of
the low and high bandpass filters. This
bandpass filter is designed to pass the
signals in the bands of frequencies.

Bandwidth can also be defined as
the frequency ranges that exist on any
point between cut off frequencies of the low and high pass filter or the band
of frequencies. The cutoff frequency 1, or we can say CF1, is
the lower frequency at which the transfer function of signals has the maximum value
equivalent to l/?2.

The cutoff
frequency 2 is the higher frequency at which the transfer function of signals has the maximum values equivalent to l/?2. The
center frequency is the frequency at which transferring of the signal function
is at maximum.

The above circuit
diagram denotes a 741 op-amp circuit. This circuit has two resistors and
two capacitors.

R1 = 2.2k?,
R2 = 22k?,    

C1 = 10nF,
C2 = 4.7nF

Central frequency   H

In the above equation: fr
represent the central frequency.

fL represent the lower
cut off frequency point.

fH represent the
higher cut off frequency point.

Using
the above information related to the circuit, we found the cut off frequencies
of the low and high pass filters in
this lab report. The input voltage of the circuit that is calculated by applying the sine waves is
used to estimate the output voltage of the
circuit. In this lab report, we
calculated and compared the cut off frequency of both low and high pass filters. We
have also calculated the experimental central frequency in this report.

Summary of
experience

The main objective of
this lab report was to perform the simulation of the bandpass filters. From this lab experience, I learned about the simulation
process. In this experiment, the simulation for both low and high
pass orders was performed. Also, the calculation of
the cut off frequencies and their comparison was
done during the experiment. From this, I can understand the
difference between the lower and higher frequencies. The formula for calculating the central frequency was also
worked out.  The calculation
of the central frequency point has shown very interesting results. Overall
it was a great learning experience to perform this lab experiment and achieving all the objectives
related to the bandpass filters.

 

Discussion
topics

The bandpass
filter can be obtained by the cascading of the low and high pass filters. The bandpass filter is used in
finding the frequencies which are either too low or too high.

The results achieved by using these
frequencies can help in finding a certain range of frequency through which we can
pass the signals.

The signals are passed by using a pair of resistors and capacitors with a
specific capacity. We use the sine waves
to apply the precise voltage as an input in
order to get the specific voltage output. In
this filter, the input of the first filter can be used as
the output of other.

With the help of input and output
values, we found the total gain that we achieved through the entire process
in the form of voltage or dB. In this lab experiment, we developed the bandpass filters by
making a stack of low pass filter and attach a high pass filter at the end of
the same stack. We also obtained the band pass
filter by making a stack of high pass filters by attaching a
low pass filter at the end.

 

Time
required

The complete lab
experiment can be completed in
approximately 1 hour.

In this 1 hour, we found all the
voltage input values for calculating
output and gain from this process. We can also found the
entire frequencies in this 1-hour process.

 

Feedback

The making of the circuit diagram, attaching the
resistors and capacitors was a very stimulating task that is associated with this experiment. The
calculation of input and output value was also a learning activity
but making the tables by using these values requires focus as these values are used for further calculation work. All
the instructions provided by the instructor were very helpful in the
completion of the experiment. 

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