WAVEFORM GENERATOR CIRCUITS USING OPERATIONAL AMPLIFIERS

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1 15EEE287 Electronic Circuits & Simulation Lab - II Lab #8 WAVEFORM GENERATOR CIRCUITS USING OPERATIONAL AMPLIFIERS OBJECTIVE The purpose of the experiment is to design and construct circuits to generate square and sine waves. The circuits include astable multivibrator, RC phase shift oscillators and Wien bridge oscillators. EQUIPMENT REQUIRED 741 Op-amp Resistors (designed values), ¼ W Potentiometer, ¼ W Capacitors (designed values) 0-30 V, 1A dc dual regulated power supply 30 MHz Oscilloscope Digital Multimeter Breadboard THEORY Astable multivibrators are square wave oscillators based on the charging and discharging of a capacitor. Oscillator is a feed back circuit where a fraction of output voltage of an amplifier is fed back to the input in the same phase. RC phase shift oscillators are sine wave oscillators which are used in the audio frequency range. The amplification is done by the op-amp and as it is used in the inverting mode it gives a phase shift of 180o. Another commonly used audio frequency oscillator is a Wien bridge oscillator. Wien Bridge is formed with a series RC network in one arm and a parallel RC network in the adjoining arm. The condition of zero phase shift around the circuit is achieved by balancing the bridge. The feedback signal in this circuit is connected to the non-inverting (+) input terminal so that the op amp is working as a non-inverting amplifier. Therefore, the feedback network need not provide any phase shift. 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,

2 15EEE287 Electronic Circuits & Simulation Lab - II Lab #8 CIRCUIT DIAGRAM Figure 1. Astable Multivibrator Figure 2. Phase shift Oscillator Figure 3. Wien-bridge Oscillator DESIGN Astable Multivibrators Square wave of frequency, f = 1 khz f = 1/2RC Choose C = 0.1uF R1 = 1.16 R2 Choose R2, then find R1. RC Phase Shift Oscillator Sine wave frequency, f = 1 khz of oscillation, f = 1/(2π 6 RC) Choose C=0.1uF Rf > 29R1 To avoid loading, R1 > 10R 65

3 15EEE287 Electronic Circuits & Simulation Lab - II Lab #8 Wien-Bridge Oscillator Sine wave frequency, f = 1 khz of oscillation, f = 1/(2πRC) Choose C=0.1uF R1 = 10R Rf = 2R1 PRACTICE PROCEDURE Astable multivibrators 1. Construct the circuit as per the diagram shown in Figure1. 2. Observe the output waveforms RC Phase shift Oscillator 1. Construct the circuit as per the diagram shown in Figure2. 2. Vary the potentiometer to start oscillation in the circuit. 3. Observe output waveforms. Wien-bridge Oscillator 1. Construct the circuit as per the diagram shown in Figure3. 2. Vary the potentiometer to start oscillation in the circuit. 3. Observe output waveforms. PRELAB 1. and create a SPICE model of astable multivibrator using op-amps. Observe the output waveforms. Compare the designed frequency and obtained frequency. 2. Extend the above circuit of astable multivibrator to generate a triangular waveform. Observe the output waveforms. 66

4 15EEE287 Electronic Circuits & Simulation Lab - II Lab #8 3. and create a SPICE model of RC phase shift oscillator using 741 op-amp to generate a sine wave of 1000 Hz. (i) Observe the output waveforms. (ii) Check the waveforms at each RC network and compare its Phase shift. (iii) Compare the designed and measure frequencies. 4. and create a SPICE model of Wien bridge oscillator using 741 op-amp to generate a sine wave of 1000 Hz. (i) Observe the output waveforms. (ii) Check the waveforms at each RC network and compare its Phase shift. (iii) Compare the designed and measure frequencies. 67

5 15EEE287 Electronic Circuits & Simulation Lab - II Lab #8 Exp. No.: Date: WAVEFORM GENERATOR CIRCUITS USING OPERATIONAL AMPLIFIERS OBJECTIVE OBSERVATION Astable Multivibrators Circuit Diagram Waveforms Table 1: Observed Output Voltage Vo p-p Volts 68

6 15EEE287 Electronic Circuits & Simulation Lab - II Lab #7 Inference RC Phase Shift Oscillator Circuit Diagram 69

7 15EEE287 Electronic Circuits & Simulation Lab - II Lab #7 Waveforms Table 1: Observed Output Voltage Vo p-p Volts Inference Wien-Bridge Oscillator 70

8 15EEE287 Electronic Circuits & Simulation Lab - II Lab #7 Circuit Diagram Waveforms Table 1: Observed Output Voltage Vo p-p Volts Inference 71

9 15EEE287 Electronic Circuits & Simulation Lab - II Lab #7 UNDERSTANDING & LEARNING 72

15EEE287 Electronic Circuits & Simulation Lab - II Lab #7 RESULTS AND CONCLUSION Prepared by: Name: Reg. No.: Actual Date of Experiment:. ASSESSMENT Date of Performance:.

10 15EEE287 Electronic Circuits & Simulation Lab - II Lab #7 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 73

LINEAR APPLICATIONS OF OPERATIONAL AMPLIFIERS

LINEAR APPLICATIONS OF OPERATIONAL AMPLIFIERS OBJECTIVE The purpose of the experiment is to examine the linear applications of an operational amplifier. The applications that are designed and analyzed