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EXPERIMENT 6
A LABORATORY DESIGN EXPERIMENT
PURPOSE: The purpose of this lab is to design simulate, build and test simple band pass filter
using passive components. The experiment is designed to provide the student with skills associated
with preparing and executing design oriented problem with minimum supervision
Introduction
A filter network is generally designed to pass signals in specific frequency range (pass band) and
reject or attenuate signals whose frequency spectrum is out tside the pass band (stop band). Ideally
we would like to have filter pass frequencies in the range WLO Sw < Whind completely reject
frequencies that are outside this band. However it not possible to design such filter with linear
circuit elements such as capacitors and resistors The characteristics of an ideal (solid) and typical
(dashed) band pass filter are given in Fig. (1).
A G(joo)
1
0.707
"LO
COHI
Figure 1. Band pass filter characteristics (frequency response).
The frequency response of band pass filter can be characterized by the following measures. The
center frequency wo the filter This is the frequency at which the maximum amplitude occurs.
The upper and lower break frequencies or the cutoff frequencies w Loand WHI The cutoff frequency
of the filter is where the amplitude is 1/12 of the maximum value. Then the width of the pass
band. called the bandwidth (BW) of the filter is given by the expression
BW WHI WLO
The design specifications for filters are given in terms of the characteristics of the frequency
response of the filter. The band pass filter that is chosen for this exercise is given in Fig. (2). It
uses cascade of high pass filter (HPF) and low pass filter (LPF) consisting entirely of
capacitors and resistors. The theoretical equations obtained via the chosen circuit can be used
together with the design specifications to find the values of the passive components.
Input
Output
Figure 2. Band-pas: filter
Note that commercially vailable capacitors and resistors take finite set of values. Hence prior
to constructing the circuit for measurements, one has to approximate the values obtain via
theoretical computations to values that are readily available in the laboratory.
The band pass filter design should consist of the following stages:
A. Theoretical calculations: Design the filter using theoretical equations and the
specifications.
B. Pspice simulation: Use the design values obtained from the previous step to simulate
the band pass filter characteristics Further fine-tuning of the passive components can
be carried out in this step to obtain the passive component values that provide the exact
design specifications.
C. Measurements: The values obtained via the simulation are used to construct the circuit
in the laboratory and relevant measurements are done to verify the characteristics
obtained via the Pspice simulation. At this stage one has to use readily available
component values in order to construct the circuit.
Design Specifications
Design the band-pass filter given in Fig(2) for WLO lower cutof frequency and WH
22n krad/s upper cutoff frequency. Note that the resistor and capacitor values should be chosen
from the range available in the laboratory
Results
The following guidelines can be used to prepare the design report in the standard lab manual
format.
STAGE/
Design your circuit based on the specifications given above for the filter shown in Fig (2). Show
all derivations and calculations used for the design Briefly describe the design approach you have
taken providing any assumptions you have made.
STAGEB
Use Pspice schematics to simulate the results from Stage A and verify that the design specifications
are met. Provide all programs and graphs to support your claims. If the theoretical values obtained
do not provide exact design specifications, describe the method you have used in order to fine-
tune the designed values.
Hint: Use the parametric sweep capability in Pspice to fine-tune the design
STAGEC
Build your circuit using discrete components and verify the designed and simulated values Collect
all relevant data to support any claims you will be making. Briefly describe the measurement
procedure. Use semilog paper or software programs like Excel to plot the frequency response of
the filter.
All results should be logically ordered in the report and sufficient information should be provided
to support any claims you are making Compare the measured results and the simulated results and
discuss any differences giving reasons.

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Laboratory 6 report

Design specifications

In this laboratory we have to design a real band pass filter, made of RC components. A band pass filter is made of a high pass filter, followed by a low pass filter.

An ideal band pass filter (or in other words an ideal network filter) allows to pass without attenuation all frequencies in a given range ω_Lo≤ω≤ω_Hi, and rejects totally all other frequencies that are outside this domain.

A real filter does the same thing, but the transitions from total rejection to zero attenuation are not abrupt as for the ideal filter. Usually real frequency filters are made with RC or RL components. They are characterized by a central frequency ω_0 (where the amplitude of the transmitted signal is maximum) and two upper ω_Hi and lower ω_Lo pass frequencies (where the amplitude...