CHARACTERISTICS OF OPERATIONAL AMPLIFIERS - II OBJECTIVE The purpose of the experiment is to examine non-ideal characteristics of an operational amplifier. The characteristics that are investigated include common-mode rejection ratio, slew rate and Gain-bandwidth product and frequency response. EQUIPMENT REQUIRED 741 Op-amp 100Ω, 100kΩ, 220kΩ resistor, ¼ W 5 kω, ¼ W potentiometer 0-30 V, 1A dc dual regulated power supply 30 MHz Oscilloscope 3 MHz Function Generator Digital Multimeter Breadboard THEORY The CMRR of an op-amp is the ratio of differential voltage gain to common-mode voltage gain. Slew rate is the maximum rate at which output voltage can be distorted. An op-amp s bandwidth is the highest undistorted frequency an op-amp can deliver. It is directly proportional to slew rate and inversely proportional to amplitude. FORMULA 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 21
CIRCUIT DIAGRAM DESIGN Inverting Amplifier Closed loop gain, ACL = Vo/Vin = -Rf/R1 Required closed loop gain = -10 Choose R1=1kΩ Non-inverting Amplifier Closed loop gain, ACL = Vo/Vin = 1+Rf/R1 Required closed loop gain = 11 Select R1=1kΩ Voltage follower Voltage follower is unity gain amplifier; closed loop gain required is 1. Consider a non-inverting amplifier. So the ratio Rf/R1 should be zero. Hence Rf = 0. PRACTICE PROCEDURE CMMR 1. Construct the circuit as shown in figure1. 2. Apply a dc voltage of 1V as input to the circuit. 22
3. Measure the output voltage. 4. Calculate CMRR Repeat the above steps for an input sinusoidal signal of 1Vp-p, 1 khz. Slew rate and Bandwidth 1. Construct the circuit as shown in figure2. 2. Apply sinusoidal signal of 2Vp-p, 1 khz. 3. Increase the frequency until the output gets distorted. 4. Measure the peak output amplitude and frequency. 5. Calculate the slew rate Repeat the above steps for square wave input. Inverting Amplifier Closed loop gain 1. Construct the circuit as per the diagram shown in Figure3. 2. Apply 100mVp-p, 1 khz sinusoidal input. 3. Observe the input and output waveforms simultaneously. Note the phase of the output with respect to input. 4. Calculate the closed loop voltage gain. Frequency Response 6. Increase the frequency until the output voltage reaches 0.707 times the input (cut-off frequency). Record the frequency. 7. Plot the frequency response using semi-log sheet. Non-inverting Amplifier Closed loop gain 1. Construct the circuit as per the diagram shown in Figure2. 2. Apply 100mVp-p, 1 khz sinusoidal input. 3. Observe the input and output waveforms simultaneously. Note the phase of the output with respect to input. 4. Calculate the closed loop voltage gain. Gain-Bandwidth product 6. Increase the frequency until the output voltage reaches 0.707 times the input (cut-off frequency). Record the frequency. 7. Calculate the gain-bandwidth product. 8. Plot the frequency response using semi-log sheet. Voltage follower 1. Construct the circuit as per the diagram shown in Figure3. 2. Apply 1Vp-p, 1 khz sinusoidal input. 3. Observe the input and output waveforms simultaneously. 23
PRELAB 1. Create gain Vs frequency plot of an op-amp using Spice tool. Analyze the bandwidth of the amplifier. 2. Design and simulate an Inverting amplifier with gain of 10 using 741 op-amp. Observe the output waveforms and plot the frequency response. Calculate the bandwidth and comment on the results obtained. 3. Design and simulate a non-inverting amplifier with gain of 10 using 741 op-amp. Observe the output waveforms and plot the frequency response. Calculate the bandwidth and comment on the results obtained. 24
Exp. No.: Date: OBJECTIVE CHARACTERISTICS OF OPERATIONAL AMPLIFIERS - II OBSERVATION CMMR Circuit Diagram Inference 25
Slew rate and Bandwidth Circuit Diagram Gain-Bandwidth Product, Gain-BW= Waveforms 26
Inference Inverting Amplifier Design Circuit Diagram Waveforms 27
Table 2.4 Frequency response of Inverting Amplifier Frequency 10 Hz Output voltage, Vo p-p Volts Calculated closed loop gain, ACL Vin = 20log(ACL) db Inference Non-Inverting Amplifier Design 28
Circuit Diagram Waveforms Table 2.5 Frequency response of Non-Inverting Amplifier Frequency 10 Hz Output voltage, Vo p-p Volts Calculated closed loop gain, ACL Vin = 20log(ACL) db 29
Inference Voltage follower Circuit Diagram Waveforms 30
Inference UNDERSTANDING & LEARNING 31
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 32