ACTIVE FILTERS USING OPERATIONAL AMPLIFIERS

Transcription

1 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 fl. The frequency range below cut off frequency is called pass band and frequency range beyond fl 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 f H is called stop band. FURTHER READING 1. Ramakand A. Gayakwad, Op-amps and linear integrated circuits, PHI learning, R.M.Marston, Op-amp Circuits Manual, Newnes, Robert Diffenderfer, Electronic Devices: Systems & Applications, Cengage Learning, 2005 CIRCUIT DIAGRAM Figure 1. First order low pass filter 74

2 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 A 0 = 1 + Choose A 0 = 2 Second order low pass filter Upper cut-off frequency, f = 1 khz Choose C = 0.1uF For second order Butterworth filter α = Pass band gain A 0 = 3 - α A 0 =

3 Second order high pass filter Lower cut-off frequency, f = 1 khz Choose C = 0.1uF For second order Butterworth filter α = Pass band gain A 0 = 3 - α A 0 = 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. 76

4 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. 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. 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. 77

5 Exp. No.: Date: ACTIVE FILTERS USING OPERATIONAL AMPLIFIERS OBJECTIVE OBSERVATION First order low pass filter Design Circuit Diagram Table 1: V in = Input frequency Output voltage, Vo p-p Volts Gain A 0 = V 0 /V in Gain in db 20log(A0) db 10 Hz 78

6 Inference Second order Butterworth low pass filter Design Circuit Diagram 79

7 Table 2: V in = Input frequency Output voltage, Vo p-p Volts Gain A 0 = V 0 /V in Gain in db 20log(A0) db 10 Hz Inference 80

8 Second order Butterworth high pass filter Design Circuit Diagram Table 3: V in = Input frequency Output voltage, Vo p-p Volts Gain A 0 = V 0 /V in Gain in db 20log(A0) db 10 Hz 81

9 Inference UNDERSTANDING & LEARNING 82

10 RESULTS AND CONCLUSION Prepared by: Name: Reg. No.: Actual Date of Experiment:. ASSESSMENT Date of Performance:.. Report Submission Date: Submission Delay:... Student Task Max. Marks Graded Marks Pre-lab Preparation 20 Inference 10 Results & Discussion 10 Signature Post-lab / Viva-voce 10 Total 50 83