EE 221 L CIRCUIT II LABORATORY 6: OP AMP CIRCUITS by Ming Zhu DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING UNIVERSITY OF NEVADA, LAS VEGAS OBJECTIVE Learn to use Op Amp to implement simple linear calculation circuits, including inverting, noninverting, summing and difference amplifiers. COMPONENTS & EQUIPMENT Power Supply Multimeter Oscilloscope Breadboard Jump wires Resistors Op Amp chip (LM741) BACKGROUND An Operational Amplifier (Op Amp) is an active electronic unit (consisting of a complex arrangement of resistors, transistors, capacitors and diodes) that behaves like a voltage-controlled voltage source (VCVS). Under certain circumstances, it can also be used in making a voltage- or current-controlled current source. An Op Amp can perform various mathematical operations such as sum signals, amplify a signal, integrate it or differentiate it. Key knowledge related to Op Amps. DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING 1
Ideal Op Amp: 1) Infinite open-loop gain, A. 2) Infinite input resistance, R i. 3) Zero output resistance, R o 0. Non-ideal Op Amp: v o = Av d = A(v 1 v 2 ) = A(V P V N ) DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING 2
Inverting Amplifier Noninverting Amplifier Summing Amplifier Difference Amplifier DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING 3
Integrator Differentiator A typical Op Amp chip and its symbol is depicted as below. Ideally, the two balance pins (1 & 5) can be omitted, and power pins (V and V + ) are omitted in schematics (must be connected to power in real applications to power on the Op Amp chip). Fig. 1. A typical Op Amp: (a) pin configuration, (b) circuit symbol LAB DELIVERIES PRELAB: 1. Review the knowledge of Op Amp circuits, part of which are listed in the previous section. DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING 4
2. Use both hand calculation and LTspice simulation to determine the voltage gain v o /v i of the following op amp circuits Assume Op Amp in each circuit is ideal. R 1 = 200Ω, R 2 = 100Ω Set v i = 3cos (2π ft), where f = 1kHz. (a) (b) LAB EXPERIMENTS: 3. Use LM/UA741 (not AD795) to implement the following circuit (Figure 2) on breadboard. Figure 2 Op Amp Output Range Circuit Figure 3 Power output for Op Amp 1) Set V+ and V- of Op Amp chip as +6V and -6V, respectively. The output of power supply should be wired as Figure 3. 2) Set input V1 as a triangular waveform, with Vpp = 0.5V and freq. = 1kHz. Use Oscilloscope to measure the corresponding output voltages. Write down Vout when it clips at a constant value (i.e. Max of Vout = ). 3) (Optional) Change V1 to a DC power supply and use multimeter for Vout. Slowly increase the voltage from 0V to 0.5V, and write down V1 = when Vout reaches its maximum. 4) Repeat 1) ~ 2), but set V+ and V- to +2V and -2V, respectively. Compare the results. DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING 5
4. Implement the circuits in Prelab 1 (a) and (b) on breadboard, respectively, and measure the voltage of v o. 1) Compare the measured results to the ones in hand calculations and LTspice simulations. What are the differences, and why? 2) Repeat Experiment 3 but change input v i from sine waveform to square waveform. POSTLAB REPORT: Include the following elements in the report document: Section Element Theory of operation 1 Include a brief description of every element and phenomenon that appear during the experiments. Prelab report 2 1. Hand calculation results of prelab circuit (a) and (b). 2. LTspice schematics and simulation results of the two circuits. Results of the experiments Experiments Experiment Results 3 1 Photos of implementations and measured results in Experiment 1 2 Photos of implementations and measured results in Experiment 2 Answer the questions 4 Questions Questions 1 What can you conclude about Op Amp? Conclusions 5 Write down your conclusions, things learned, problems encountered during the lab and how they were solved, etc. Images Paste images (e.g. scratches, drafts, screenshots, photos, etc.) in Postlab report document (only.docx,.doc or.pdf format is accepted). If the sizes of images are too large, convert them to jpg/jpeg format first, and then paste them in the document. 6 Attachments (If needed) Zip your projects. Send through WebCampus as attachments, or provide link to the zip file on Google Drive / Dropbox, etc. REFERENCES & ACKNOWLEDGEMENT 1. C. K. Alexander and M. Sadiku, Fundamentals of Electric Circuits, 4 th Ed. 2. http://www.ti.com/lit/ds/symlink/lm741.pdf 3. http://www.ti.com/lit/ds/symlink/ua741.pdf I appreciate the help from faculty members and TAs during the composing of this instruction manual. I would also thank students who provide valuable feedback so that we can offer better higher education to the students. DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING 6