15EEE287 Electronic Circuits & Simulation Lab - II
Lab #9
ACTIVE FILTERS USING OPERATIONAL AMPLIFIERS
OBJECTIVE
The purpose of the experiment is to design and compare the frequency plots of second order low pass and high
pass active filters.
EQUIPMENT REQUIRED
741 Op-amp
Resistors (designed values), ¼ W
Capacitors (designed values)
0-30 V, 1A dc dual regulated power supply
3 MHz Function Generator
30 MHz Oscilloscope
Digital Multimeter
Breadboard
THEORY

A filter is a frequency selective circuit that allows only a certain band of frequency component of an input
signal to pass through and blocks other frequency components.

An active filter network is obtained by interconnecting passive elements and active element .Op-amps are
used in active filters to provide amplification and gain control.

A low pass filter allows only low frequency signals and suppresses high frequency signals.

The range of frequency varies from dc to cut off frequency f L . The frequency range below cut off
frequency is called pass band and frequency range beyond f L is called stop band.

A high pass filter allows only high frequency signals and suppresses low frequency signals.

The range of frequency beyond cut off frequency f H is called pass band and range of frequency from dc to
fH is called stop band.
FURTHER READING
1. Ramakand A. Gayakwad, “Op-amps and linear integrated circuits”, PHI learning, 2009.
2. R.M.Marston, “Op-amp Circuits Manual”, Newnes, 1989.
3. Robert Diffenderfer, “Electronic Devices: Systems & Applications”, Cengage Learning, 2005
CIRCUIT DIAGRAM
Figure 1. First order low pass filter
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Department of Electrical & Electronics Engineering, Amrita School of Engineering, Coimbatore.
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15EEE287 Electronic Circuits & Simulation Lab - II
Lab #9
Figure 2. Second order Butterworth low pass filter
Figure 3. Second order Butterworth high pass filter
DESIGN
First order low pass filter
Upper cut-off frequency, f = 1 kHz
Choose C = 0.1uF
Pass band gain A0 = 1 +
Choose A0 = 2
Second order low pass filter
Upper cut-off frequency, f = 1 kHz
Choose C = 0.1uF
For second order Butterworth filter α = 1.414.
Pass band gain A0 = 3 - α
A0 = 1 +
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15EEE287 Electronic Circuits & Simulation Lab - II
Lab #9
Second order high pass filter
Lower cut-off frequency, f = 1 kHz
Choose C = 0.1uF
For second order Butterworth filter α = 1.414.
Pass band gain A0 = 3 - α
A0 = 1 +
PRACTICE PROCEDURE
First order low pass filter
1. Construct the circuit as per the diagram shown in Figure1.
2. Apply 1 V peak-peak sinusoidal signal at the output.
3. Observe simultaneously the input and output waveforms on the oscilloscope.
4. Vary the frequency of the input signal from 10Hz to 100 kHz. Measure the output amplitude
corresponding to different frequencies and compute the gain.
5. Plot the frequency response on a semi-log sheet with gain in dB on y-axis and frequency in Hz on x-axis.
Second order low pass filter
1. Construct the circuit as per the diagram shown in Figure2.
2. Apply 1 V peak-peak sinusoidal signal at the output.
3. Observe simultaneously the input and output waveforms on the oscilloscope.
4. Vary the frequency of the input signal from 10Hz to 100 kHz. Measure the output amplitude
corresponding to different frequencies and compute the gain.
5. Plot the frequency response on a semi-log sheet with gain in dB on y-axis and frequency in Hz on x-axis.
Second order high pass filter
1. Construct the circuit as per the diagram shown in Figure3.
2. Apply 1 V peak-peak sinusoidal signal at the output.
3. Observe simultaneously the input and output waveforms on the oscilloscope.
4. Vary the frequency of the input signal from 10Hz to 100 kHz. Measure the output amplitude
corresponding to different frequencies and compute the gain.
5. Plot the frequency response on a semi-log sheet with gain in dB on y-axis and frequency in Hz on x-axis.
PRELAB
1. Design and simulate a first order low pass filter with upper cut off frequency of 1 kHz. Plot the frequency
analysis. Observe the cut-off frequency from the plot.
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15EEE287 Electronic Circuits & Simulation Lab - II
Lab #9
2. Design and simulate a second order Butterworth low pass filter with upper cut off frequency of 1 kHz. Plot the
frequency analysis. Observe the cut-off frequency from the plot. Compare the frequency plot with that of the
first order filter.
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3. Design and simulate a first order high pass filter with lower cut off frequency of 1 kHz. Plot the frequency
analysis. Observe the cut-off frequency from the plot.
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4. Design and simulate a second order Butterworth high pass filter with lower cut off frequency of 1 kHz. Plot the
frequency analysis. Observe the cut-off frequency from the plot.
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15EEE287 Electronic Circuits & Simulation Lab - II
Lab #9
Exp. No.:
Date:
ACTIVE FILTERS USING OPERATIONAL AMPLIFIERS
OBJECTIVE
OBSERVATION
First order low pass filter
Design
Circuit Diagram
Table 1:
Input
frequency
10 Hz
Output voltage,
Vo p-p Volts
Gain A0 = V0/Vin
Vin =
Gain in dB
20log(A0) dB
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15EEE287 Electronic Circuits & Simulation Lab - II
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Inference
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Second order Butterworth low pass filter
Design
Circuit Diagram
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15EEE287 Electronic Circuits & Simulation Lab - II
Table 2:
Input
frequency
10 Hz
Output voltage,
Vo p-p Volts
Lab #9
Gain A0 = V0/Vin
Vin =
Gain in dB
20log(A0) dB
Inference
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Department of Electrical & Electronics Engineering, Amrita School of Engineering, Coimbatore.
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15EEE287 Electronic Circuits & Simulation Lab - II
Lab #9
Second order Butterworth high pass filter
Design
Circuit Diagram
Table 3:
Input
frequency
10 Hz
Output voltage,
Vo p-p Volts
Gain A0 = V0/Vin
Vin =
Gain in dB
20log(A0) dB
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15EEE287 Electronic Circuits & Simulation Lab - II
Lab #9
Inference
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UNDERSTANDING & LEARNING
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15EEE287 Electronic Circuits & Simulation Lab - II
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RESULTS AND CONCLUSION
Prepared by:
Name: __________________________________________
Reg. No.: _________________________
Actual Date of Experiment: ………………………….
ASSESSMENT
Date of Performance: …………………..
Student Task
Report Submission Date: ……………
Pre-lab Preparation
20
Inference
10
Results & Discussion
10
Post-lab / Viva-voce
10
Total
50
Max. Marks
Graded Marks
Submission Delay: …........
Signature
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