LABORATORY MANUAL DEPARTMENT OF ELECTRICAL & COMPUTER ENGINEERING UNIVERSITY OF CENTRAL FLORIDA EEL 4309 ELECTRONICS II PREPARED BY

Transcription

1 LABORATORY MANUAL DEPARTMENT OF ELECTRICAL & COMPUTER ENGINEERING UNIVERSITY OF CENTRAL FLORIDA EEL 4309 ELECTRONICS II PREPARED BY DR. TAKIS KASPARIS REVISED SPRING 2005

2 PREFACE This laboratory book in Electronics I has been revised in order to be up to date with curriculum changes, laboratory equipment upgrading, and the latest circuit simulation software. Every effort has been made to correct all the known errors, but nobody is perfect. If you find any additional errors or anything else that you think is an error, please contact Dr. Kasparis at: kasparis@ee.ucf.edu The contribution of Mr. Enrique Tecincella who diligently worked to re-draw all the figures in this manual needs to be acknowledged. Dr. Takis Kasparis Spring

3 TABLE OF CONTENTS SAFETY RULES AND OPERATING PROCEDURES LABORATORY SAFETY INFORMATION GUIDELINES FOR LABORATORY NOTEBOOK TROUBLESHOOTING HINTS EXPERIMENT # 1 LINEAR OP-AMP APPLICATIONS PART I EXPERIMENT # 2 LINEAR OP-AMP APPLICATIONS PART II EXPERIMENT # 3 ACTIVE FILTERS EXPERIMENT # 4 PRECISION DIODES AND APPLICATIONS EXPERIMENT # 5 COMPARATORS AND SCHMITT TRIGGERS EXPERIMENT # 6 DESIGN PROJECT EXPERIMENT # 7 WAVEFORM GENERATORS EXPERIMENT # TIMER EXPERIMENT EVALUATION FORM APPENDIX : LIST OF AVAILABLE RESISTORS AND CAPACITORS RESISTOR COLOR CODE TUTORIAL SPECIFICATIONS OF SELECTED COMPONENTS 3

4 Safety Rules and Operating Procedures 1. Note the location of the Emergency Disconnect (red button near the door) to shut off power in an emergency. Note the location of the nearest telephone (map on bulletin board). 2. Students are allowed in the laboratory only when the instructor is present. 3. Open drinks and food are not allowed near the lab benches. 4. Report any broken equipment or defective parts to the lab instructor. Do not open, remove the cover, or attempt to repair any equipment. 5. When the lab exercise is over, all instruments, except computers, must be turned off. Return substitution boxes to the designated location. Your lab grade will be affected if your laboratory station is not tidy when you leave. 6. University property must not be taken from the laboratory. 7. Do not move instruments from one lab station to another lab station. 8. Do not tamper with or remove security straps, locks, or other security devices. Do not disable or attempt to defeat the security camera. 9. ANYONE VIOLATING ANY RULES OR REGULATIONS MAY BE DENIED ACCESS TO THESE FACILITIES. I have read and understand these rules and procedures. I agree to abide by these rules and procedures at all times while using these facilities. I understand that failure to follow these rules and procedures will result in my immediate dismissal from the laboratory and additional disciplinary action may be taken. Signature Date Lab # 4

5 Laboratory Safety Information Introduction The danger of injury or death from electrical shock, fire, or explosion is present while conducting experiments in this laboratory. To work safely, it is important that you understand the prudent practices necessary to minimize the risks and what to do if there is an accident. Electrical Shock Avoid contact with conductors in energized electrical circuits. Electrocution has been reported at dc voltages as low as 42 volts. Just 100ma of current passing through the chest is usually fatal. Muscle contractions can prevent the person from moving away while being electrocuted. Do not touch someone who is being shocked while still in contact with the electrical conductor or you may also be electrocuted. Instead, press the Emergency Disconnect (red button located near the door to the laboratory). This shuts off all power, except the lights. Make sure your hands are dry. The resistance of dry, unbroken skin is relatively high and thus reduces the risk of shock. Skin that is broken, wet or damp with sweat has a low resistance. When working with an energized circuit, work with only your right hand, keeping your left hand away from all conductive material. This reduces the likelihood of an accident that results in current passing through your heart. Be cautious of rings, watches, and necklaces. Skin beneath a ring or watch is damp, lowering the skin resistance. Shoes covering the feet are much safer than sandals. If the victim isn't breathing, find someone certified in CPR. Be quick! Some of the staff in the Department Office are certified in CPR. If the victim is unconscious or needs an ambulance, contact the Department Office for help or call 911. If able, the victim should go to the Student Health Services for examination and treatment. Fire Transistors and other components can become extremely hot and cause severe burns if touched. If resistors or other components on your proto-board catch fire, turn off the power supply and notify the instructor. If electronic instruments catch fire, press the Emergency Disconnect (red button). These small electrical fires extinguish quickly after the power is shut off. Avoid using fire extinguishers on electronic instruments. Explosion When using electrolytic capacitors, be careful to observe proper polarity and do not exceed the voltage rating. Electrolytic capacitors can explode and cause injury. A first aid kit is located on the wall near the door. Proceed to Student Health Services, if needed. 5

6 GUIDELINES FOR LABORATORY NOTEBOOK The laboratory notebook is a record of all work pertaining to the experiment. This record should be sufficiently complete so that you or anyone else of similar technical background can duplicate the experiment and data by simply following your laboratory notebook. Record everything directly into the notebook during the experiment. Do not use scratch paper for recording data. Do not trust your memory to fill in the details at a later time. Organization in your notebook is important. Descriptive headings should be used to separate and identify the various parts of the experiment. Record data in chronological order. A neat, organized and complete record of an experiment is just as important as the experimental work. 1. Heading: The experiment identification (number) should be at the top of each page. Your name and date should be at the top of the first page of each day's experimental work. 2. Object: A brief but complete statement of what you intend to find out or verify in the experiment should be at the beginning of each experiment. 3. Diagram: A circuit diagram should be drawn and labeled so that the actual experiment circuitry could be easily duplicated at any time in the future. Be especially careful to record all circuit changes made during the experiment. 4. Equipment List: List those items of equipment which have a direct effect on the accuracy of the data. It may be necessary later to locate specific items of equipment for rechecks if discrepancies develop in the results. 5. Procedure: In general, lengthy explanations of procedures are unnecessary. Be brief. Short commentaries along side the corresponding data may be used. Keep in mind the fact that the experiment must be reproducible from the information given in your notebook. 6. Data: Think carefully about what data is required and prepare suitable data tables. Record instrument readings directly. Do not use calculated results in place of direct data; however, calculated results may be recorded in the same table with the direct data. Data tables should be clearly identified and each data column labeled and headed by the proper units of measure.. 7. Calculations: Not always necessary but equations and sample calculations are often given to illustrate the treatment of the experimental data in obtaining the results 8. Graphs: Graphs are used to present large amounts of data in a concise visual form. Data to be presented in graphical form should be plotted in the laboratory so that any questionable data points can be checked while the experiment is still set up. The grid lines in the notebook can be used for most graphs. If special graph paper is required, affix the graph permanently into the notebook. Give all graphs a short descriptive title. Label and scale the axes. Use units of measure. Label each curve if more than one on a graph. 9. Results: The results should be presented in a form which makes the interpretation easy. Large amounts of numerical results are generally presented in graphical form. Tables are generally used for small amounts of results. Theoretical and experimental results should be on the same graph or arrange in the same table in a way for easy correlation of these results. 10. Conclusion: This is your interpretation of the results of the experiment as an engineer. Be brief and specific. Give reasons for important discrepancies. 6

7 TROUBLESHOOTING HINTS 1. Be sure that the power is turned on. 2. Be sure the ground connections are common. 3. Be sure the circuit you built is identical to that in the diagram. (Do a node-by-node check.) 4. Be sure that the supply voltages are correct. 5. Be sure that the equipment is set up correctly and you are measuring the correct parameter. 6. If steps 1 through 5 are correct, then you probably have used a component with the wrong value or one that doesn't work. It is also possible that the equipment does not work (although this is not probable) or the protoboard you are using may have some unwanted paths between nodes. To find your problem you must trace through the voltages in your circuit node by node and compare the signal you have to the signal you expect to have. Then if they are different use your engineering judgement to decide what is causing the different or ask your lab assistant. 7

8 EXPERIMENT # 1 LINEAR OP-AMP APPLICATIONS PART I OBJECTIVES: EQUIPMENT: To study the Op-Amp used in inverting and non-inverting amplifiers, inverting summing amplifier, integrator and differentiator. Oscilloscope Function Generator LF 351 Op-Amp Capacitors Resistors BACKGROUND: Op-Amp circuits employing negative feedback can be used in various configurations. Since in these applications there is a linear relation between input(s) and output, we usually refer to these application circuits as linear applications. Negative feedback produces bounded input-bounded output stability; i.e. a finite input voltage cannot produce an infinite output voltage INVERTING CONFIGURATION: The basic Inverting configuration is shown in Figure 1. Because of the virtual short and because the noninverting terminal is grounded, we say that there is a virtual ground at the inverting terminal. NON-INVERTING CONFIGURATION: The basic non-inverting configuration is shown in Figure 2. Voltage follower: A particularly simple version of the non-inverting circuit with unity gain is the voltage follower shown in Figure 3. INVERTING SUMMING AMPLIFIER: By adding additional input resistors to the basic inverting circuit of Figure 1, we have the summing amplifier (inverting) shown in Figure 4 with three inputs. INVERTING INTEGRATOR: the inverting integrator is shown in Figure 5. INVERTING DIFFERENTIATOR: By reversing the resistor and the capacitor, we get the inverting differentiator shown in Figure 6. PREPARATION/DESIGN: A) INVERTING AMPLIFIER: Design inverting amplifiers with gain -1 and -10 and input impedance of at least 1K. Use available resistor values. 8

9 B) NON-INVERTING AMPLIFIER: Design non-inverting amplifiers with gain 1and 10. Use available resistor values. C) SUMMING AMPLIFIER: Design a summing amplifier to implement the function V o = V 1 + 2V ) D) INVERTING INTEGRATOR: ( 2 Design an integrator circuit so that when the input is a sine wave of frequency 1 KHz, the output voltage has the same amplitude (unity gain). E) INVERTING DIFFERENTIATOR: Design a differentiator circuit so that when the input is a sine wave of frequency 1 KHz, the output voltage has the same amplitude (unity gain). COMPUTER SIMULATION: A) INVERTING AND NON-INVERTING AMPLIFIERS: For the designed circuits in preparation parts A and B, plot the voltage gain as function of the frequency in the range 0 to 50KHz. B) SUMMING AMPLIFIER: For the circuit you have designed in preparation part C, generate the output voltage waveform if V 1 is a sine wave or a square-wave of 2 volt peak (0-peak), and V 2 is a DC voltage of 1V. C) INTEGRATOR AND DIFFERENTIATOR: For the circuits you have designed in preparation parts D and E, generate the output voltage waveform if the input is a sine wave or a square-wave of 2 volt peak (0-peak) and of frequencies 500 Hz, 1 KHz, and 2 KHz. EXPERIMENT: In all the experimental parts use the LF 351 Op-Amp with a split power supply voltage of ±12V. A) INVERTING AMPLIFIER: 1) Build the circuits you have designed in the preparation part 1and verify their operation. 2) Modify your design for gain of 10 as shown in circuit of Figure 7 by adding the 56K (or any other close value). Set the function generator so that V g is a sine wave of 1V amplitude and 1 KHz frequency. Measure the following voltage gains: Vo Vo A f 1 = and A f 2 = V V 3) Measure the input resistance Z i. i g 9

10 B) NON-INVERTING AMPLIFIER: 1) Build the circuits you have designed in the preparation part 2, and measure the voltage gain. 2) Modify your design for gain of 10 as shown in circuit of Figure 8 by adding the 56K (or any other close value) resistors. Set the function generator so that Vg is a sine wave of 1V amplitude and 1 KHz frequency. Measure the following voltage gains: V o A f 1 = and V i V A f 2 = V o g Compare the two voltage gains you just measured. Why are they equal? Measure the input resistance R i. C) SUMMING AMPLIFIER: Build the circuit you have designed in preparation part C. Observe and sketch the output voltage waveform if V 1 is a sine wave or a square wave of 2 volts peak (0-peak) and V 2 is a DC voltage of 1V. Vary the input voltage V2 and observe the result. D) INTEGRATOR: 1) Build the circuit you have designed in preparation part D. Observe and sketch the output voltage waveform if the input is a sine wave, square wave and triangular wave of 2 volt peak (0-peak) and of frequencies 500 Hz, 1 KHz, and 2 KHz. 2) For any of the cases in (1) notice that the output voltage is not centered around zero. By Using a DC offset in the input (there is one such control on the function generator) try to center it around the zero level. Why is it almost impossible? E) DIFFERENTIATOR 1) Build the circuit you have designed in preparation part E. Repeat all the experimental steps in the integrator part (1) for the differentiator too. REPORT: In your report present experimental results and compare them with the expected results. Discuss any discrepancies, make comments and write conclusions. REFERENCES: Current textbook for EEL

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12 EXPERIMENT # 2 LINEAR OP-AMP APPLICATIONS PART II OBJECTIVES: To study the Op-Amp used in difference amplifier circuits, all-pass filter, voltage to current converter and non-inverting integrator. EQUIPMENT: Oscilloscope Function Generator LF 351 Op-Amp Capacitors Resistors BACKGROUND: This experiment is a continuation of experiment 1. Refer to the general background section of experiment 1. DIFFERENCE AMPLIFIER: A difference amplifier has two inputs and the output voltage is proportional to the voltage difference of the input voltages. In fact, the (open-loop) Op-Amp itself is a difference amplifier, except that the gain is ideally infinity. Here we want a difference amplifier with finite gain. One such circuit using a single Op-Amp is shown in Figure 1. ALL-PASS FILTER: An all-pass filter has a flat magnitude frequency response over the entire frequency range of interest, and linear phase with adjustable slope. In this sense, the all-pass filter is actually a phase shifter. One such circuit can be most easily designed using a single Op-Amp as shown in Figure 3 VOLTAGE TO CURRENT CONVERTER: A voltage to current converter produces a current into a load that is independent of the value of the load, and is also proportional to an input voltage. Thus, if the input voltage is constant, the circuit will deliver a constant current into the load, acting as a constant current source. One such circuit using a single Op-Amp is shown in Figure 4. NON-INVERTING INTEGRATOR: A non-inverting integrator can be obtained by cascading an inverting integrator and an inverting amplifier. However, this approach requires two Op-Amps. A non-inverting integrator using a single Op-Amp can be obtained if in the voltage to current converter the load is a capacitor as shown in Figure 5 PREPARATION / DESIGN: 1) Consider the difference amplifier and the voltage divider as shown in Figure 6. The input voltage is a sinusoid with 10V amplitude. Compute the common and the difference voltages to the amplifier if the difference amplifier inputs are connected between points a-b and between c-d. Assuming a properly calibrated circuit, compute the output for each case. Note: Resistors R s may have any available value from 10Ω to 100Ω and resistors R may have any available value from 1KΩ to 50KΩ. 12

13 4) For the non-inverting integrator of Figure 5, compute values of R, C so that if the input is a sinusoid of frequency 1 KHz, then the amplitude of the output is approximately the same as the amplitude of the input. COMPUTER SIMULATION: Simulate the all pass filter and the non-inverting integrator and check agreement with the theoretically expected results. EXPERIMENT: A) DIFFERENCE AMPLIFIER 1) Consider the circuit of Figure 6. Carry-out the calibration steps described in class. 2) Set the input to a 10V sine wave and measure the output if the inputs are connected to points a-b (as shown) and when they are moved to points c-d. 3) Slightly misadjust the variable resistor labeled "ratio" and measure the resulting common gain (assume that the difference gain did not change significantly). Compute the CMMR. B) ALL-PASS FILTER 1) Build the all-pass filter circuit using the component values found in part 2 of the preparation and verify that the circuit produces the correct phase shift on sinusoidal input. 2) Vary the input frequency observing both input and output. What do you notice? 3) Use a variable resistor in place of R. Vary R observing both input and output. What do you notice? C) VOLTAGE TO CURRENT CONVERTER 1) Build the circuit using the component values found in part 3 of the preparation. Use a 10K variable resistor for R L. Use the DMM to measure the current in R L. Connect the input to the 5V section of the power supply. 2) Keep R L fixed to a value around 2K and vary the input voltage. Verify that the voltage to current conversion is correct, i.e., 1V produces 1mA, 2V produce 2mA and so on. Make sure the Op-Amp does not saturate. 3) Keep the input voltage to 1V and vary R L. Verify that the current remains constant. Determine the range of R L where the current remains constant. Is this the range you have predicted from the preparation? D) NON-INVERTING INTEGRATOR 1) Build the non-inverting integrator by simply modifying the voltage to current converter of the previous part and by using the component values found in the preparation part 5. Verify that the circuit works correctly. How do you see that this integrator is non-inverting? REPORT: In your report present experimental results and compare them with the expected results. Discuss any discrepancies, make comments and write conclusions. REFERENCES: Current textbook for EEL

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15 EXPERIMENT # 3 ACTIVE FILTERS OBJECTIVES: To study the design and implementation of low-pass, high-pass and band-pass active filters. EQUIPMENT: Oscilloscope Function Generator LF 351 Op-Amps Capacitors Resistors BACKGROUND: A filter design problem has two phases. In the first phase, a transfer function with the desired frequency response is derived. The second phase is the design of a circuit (active or passive) that implements the transfer function. There are a wide variety of active filter circuit implementations. These circuits essentially implement transfer functions of first, second, third, and sometimes fourth order. A very popular circuit for second order low-pass and high-pass transfer functions was developed by Sallen and Key and the low-pass version is shown in Figure 1. The circuit of Figure 2 can be used to implement first order transfer functions. A high-pass prototype can be obtained by simply interchanging the positions of R and C in Figures 1 and 2 (without changing the positions of R1 and R 2 ). PREPARATION/DESIGN: 1) Design either a low or high pass filter of at least third order. Specify the following: a) Type and order of the filter. b) Cut-off frequency. You can use the Tables at the end of this experiment and the design procedure described in class. COMPUTER SIMULATION: Perform a PSpice simulation of all the filters you have designed. EXPERIMENT: The purpose of the experimental part is to build and test your designed filters. A) LOW OR HIGH PASS. Build the filter you have designed and obtain the experimental frequency response. Measure the cut-off frequency. REPORT: In your report present experimental results and compare them with the expected results. Discuss any discrepancies, make comments and write conclusions. Your report should include the following: a) Complete filter specifications. b) Summary of design steps. c) Complete circuit design. d) Computer simulation using LF 351 Op-Amps. e) Laboratory obtained experimental results. f) Summary and conclusions. REFERENCES: Current textbook for EEL

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17 EXPERIMENT # 4 PRECISION DIODES AND APPLICATIONS OBJECTIVES: To study the characteristics and the applications of precision diodes designed using PN diodes and Op-Amps. EQUIPMENT: Oscilloscope Function Generator LF 351 Op-Amp 1N4148 BACKGROUND: Diodes find numerous applications in practice, including rectifiers, envelope detectors, clipping, clamping and other signal processing circuits. One limitation of p-n diodes is that for small forward voltages the current is practically zero. For the current to become appreciable, the voltage should exceed a threshold value sometimes referred as the "cut-in" voltage which is typically 0.65V to 0.7V for silicon. A precision diode can be obtained by placing a diode in the negative feedback path of an Op-Amp as shown in Figure 1. The transfer characteristic is also shown. An alternate circuit where the Op-Amp does not saturate is shown in Figure 2. A) RECTIFIERS: A conventional half-wave diode rectifier is shown in Figure 3.a and the precision half-wave rectifier is shown in Figure 3.b. In both circuits the diode eliminates the negative cycles of the input voltage. It is possible to design a full-wave rectifier using only two Op-Amps. One possible configuration is shown in Figure 4. Note that this circuit is essentially the precision diodes of Figure 1.a and 2.a connected in parallel. Other configurations are also possible B) LIMITERS: A soft-limiting circuit is shown in Figure 5.a. The associated transfer characteristic with the various break points and slopes is shown in Figure 5.b. Note that when R 2 << R F, and R 3 << R F the circuit becomes a hardlimiter. If in addition R A << R F, then the circuit becomes a very hard-limiter. PREPARATION: a) Explain the operation of the circuit in Figure 4. b) For all the circuits in Figures 3 and 4 draw the output waveforms assuming a sinusoidal input of 1V amplitude. c) Verify the various break points and slopes on the transfer characteristic of in Figure 5.b. Compute the values of break points and slopes assuming the following values: R F = R A = 100KΩ, R 3 = 10 KΩ, R 4 = 20KΩ, R 2 = 15KΩ, R 1 = 20 KΩ, V R = 9V Plot the output waveform assuming a sinusoidal input of sufficiently large amplitude. 17

18 EXPERIMENT: The purpose of the experiment is to study the characteristics of various application circuits of the precision diode in the lab. In all the experiments use the LF 351 Op-Amp with a power supply of V CC = ±9V. A) RECTIFIERS. a) Connect the circuit of Figure 3.a and let the input be a sinusoid waveform of frequency 1 KHz. Observe the output waveform when the amplitude of the input varies from 0V to 5V. b) Connect the circuit of Figure 3.b and repeat part (a). Display the transfer characteristic dynamically on the scope. Increase the input frequency and find the highest frequency for which the circuit still performs satisfactorily. Repeat this part using the faster circuit in Figure 2.a and compare the results. c) Repeat the steps in (b) for the circuit of Figure 4 and compare the results. B) LIMITERS a) Connect the circuit of Figure 5.a using the same values as in the preparation part, namely: R F = R A = 100KΩ, R 3 = 10 KΩ, R 4 = 20KΩ, R 2 = 15KΩ, R 1 = 20 KΩ, V R = 9V Note that V R1,2 are the same as the Op-Amp power supplies. Display the transfer characteristic dynamically on the oscilloscope. Measure the various break points and check agreement with the theoretical values. b) Remove R F and repeat part (a). REPORT: In your report present experimental results and compare them with the expected results. Discuss any discrepancies, make comments and write conclusions. REFERENCES: Current textbook for EEL

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20 EXPERIMENT # 5 VOLTAGE COMPARATORS AND SCHMITT TRIGGERS OBJECTIVES: To study the operation and the applications of comparators and Schmitt triggers in waveshaping applications. EQUIPMENT: Oscilloscope Function Generator LF 351 Op-Amp LM 393 Comparator Resistors BACKGROUND: Voltage comparators are used in numerous applications in practice, including wave-shaping, waveform generation, interfacing between analog and digital circuits, controllers etc. There are in general three classes of voltage comparators; the single threshold comparator, two threshold with hysteresis (Schmitt trigger), and two threshold without hysteresis (window comparator). In this experiment we will study the first two types. A) COMPARATOR: Single threshold voltage comparators compare two voltages and provide a binary output that indicates which of the two voltages is higher. Most of the times a high gain Op-Amp operated open-loop as shown in Figure 1.a, can be used as a comparator. The associated transfer characteristic is shown in Figure 1.b. Opencollector outputs require an external pull-up resistor between the output terminal and the power supply as shown in Figure 2.a and the transfer characteristic is shown in Figure 2.b B) SCHMITT TRIGGER: The Schmitt trigger is a voltage comparator with positive feedback, as opposed to the open-loop (no feedback) comparator. The input voltage values that cause the output change from one state to the other are usually called transition or firing voltages. The distance between the firing voltages is called the hysteresis. Schmitt triggers using Op-Amps can be configured in two ways; inverting and non-inverting. A typical inverting circuit is shown in Figure 3.a with the associated transfer characteristic shown in Figure 3.b A typical non-inverting circuit is shown in Figure 4.a with the associated transfer characteristic shown in Figure 4.b. PREPARATION: For the LF 351 assume that V CC =±12V and V oh =V CC, V ol = -V CC. a) Consider the circuit of Figure 1 and assume that the input is a triangular wave with peak values ±9V. Draw the input and the output if V R = 0V, 1V, 3V. b) Repeat part (a) if V i and VR are interchanged. c) Refer to Figures 3 and 4. In Figure 3 let R 1 = R 2 = 100K and in Figure let R 1 = 200K and R 2 = 100K. For each circuit repeat part (a) above. 20

21 d) Repeat parts (a) and (c) if the LF 351 is replaced with the LM 393. Note that the LM 393 has open collector output and it needs a pull-up resistor (use anything from 2.2K to 4.7K). Note also that the output levels are now different. EXPERIMENT: The purpose of the experiment is to study the operation of the comparators and the Schmitt triggers in the lab, and to verify the theoretically expected results. The reference voltage V R can be taken from the 5V side of the power supply. A) COMPARATORS a) Connect the circuit of Figure 1 and perform parts (a) and (b) of the preparation (assume 1KHz triangular wave). Mark the transition points. Vary the reference voltage V R and observe the result. b) Display the transfer characteristic of the circuit on the oscilloscope and identify the transition points. Vary the reference voltage V R and observe the result. Increase the input frequency and notice if there is any result. Can you explain what you see? c) Connect the circuit of Figure 2 and perform part (a) of the preparation (assume 1KHz triangular wave). Mark the transition points. Vary the reference voltage V R and observe the result. B) SCHMITT-TRIGGER a) Connect the circuits of Figures 3 and 4 and perform part (c) of the preparation. Mark the transition points (firing voltages). b) Display the transfer characteristic of each circuit on the oscilloscope and identify the transition points. Vary the reference voltage V R and observe the result. Increase the input frequency and notice if there is any result. Can you explain what you see? c) In either Figure 3 or 4 replace the LF 351 with the LM 393 and repeat the steps in (a) and (b) above. REPORT: In your report present experimental results and compare them with the expected results. Discuss any discrepancies, make comments and write conclusions. REFERENCES: Current textbook for EEL

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23 EXPERIMENT # 6 DESIGN PROJECT: To be assigned by course instructor. 23

24 EXPERIMENT # 7 WAVEFORM GENERATORS OBJECTIVES: To study the application of comparators and Schmitt triggers in square and triangular waveform generators. In addition, a sinusoidal generator is also studied. EQUIPMENT: Oscilloscope Function Generator LF 351 Op-Amp LM 393 Comparator Resistors Capacitors BACKGROUND: One application of comparators and Schmitt triggers is in waveform generators, particularly square and triangular waves. Sinusoidal waveforms can be generated in several ways and there is a vast literature where the interested reader can find all the details. Consult also with the references at the end. For frequencies up to a few MHz, RC oscillators using Op-Amps dominate because they are easy to design. A major difficulty with sinusoidal oscillators is the start-up of the oscillations and the stabilization of the amplitude of the oscillations. Various approaches are used to overcome these two difficulties. A) SQUARE WAVE: A simple, yet effective square wave generator is shown in Figure 1. This circuit is actually an inverting Schmitt trigger and an RC network. The maximum frequency that can be generated by this circuit is limited by the speed of the Op-Amp. B) TRIANGULAR WAVE: By using a non-inverting Schmitt trigger and an integrator in a closed loop as shown in Figure 2, it is possible to generate both triangular and square waves. The integrator integrates the square-wave and converts it into a triangular wave. C) SINE WAVE Among the several RC Op-Amp oscillators, the Wein-bridge is popular. The basic Wein-bridge oscillator is shown in Figure 3. It consists of a non-inverting amplifier and the series/parallel RC voltage divider (Wein bridge) that provides positive feedback to the Op-Amp. It can be shown that if the gain of the non-inverting amplifier is 3, the circuit will oscillate at a single frequency, and the frequency of the oscillations is given by: ω = o 1 RC 24

25 PREPARATION: For the LF 351 assume that V CC = ± 12V and VoH VCC, VoL = VCC. a) With component values as shown and R1 = R 2 calculate the frequency of the oscillations in Figure 1. b) With component values as shown and R any convenient value between 1K and 10K, calculate the frequency of the oscillations in Figures 2. c) Calculate the frequency of the oscillations of the Wein-bridge oscillator in Figure 3. COMPUTER SIMULATION: Perform a computer simulation of the Wein-bridge oscillator of Figure 3. EXPERIMENT: The purpose of the experiment is to experimentally verify the functionality of the circuits and check discrepancies from theoretically expected results. Use the LF351 with power supplies V CC = ±12V. A) SQUARE WAVE Set V R =0. a) Connect the circuit of Figure 1 and check that it works as expected. Display on separate oscilloscope channels the voltage across the capacitor and the output voltages. b) Vary the voltage V R and observe the effect on the wave shape. Can this adjustment be of any value? Can you think of some applications? c) By using various capacitor values determine the maximum frequency of the oscillations where the waveform is still an acceptable square wave. B) TRIANGULAR WAVE a) Connect the circuit of Figures 2 and verify that works as expected. b) Display on the oscilloscope both the triangular and the square-wave outputs. c) Replace R by a 10K variable resistor and by varying R observe the relation between the triangular and the square waves. d) Replace R 2 by a 10K variable resistor and by varying R 2 observe the relation between the triangular and the square waves. e) Disconnect the inverting terminal of the Schmitt-trigger from the ground and connect it to the 5V side of the power supply. Vary the voltage and observe the result. Can you explain what you see? 25

26 C) SINE WAVE a) Connect the circuit of Figure 3 and adjust the variable resistor until oscillations begin. Observe the effect of further adjustment on the shape of the oscillations. REPORT: In your report present experimental results and compare them with the expected results. Discuss any discrepancies, make comments and write conclusions. REFERENCES: Current textbook for EEL

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28 EXPERIMENT # TIMER OBJECTIVES: To study the monostable and astable modes of the 555 Timer. EQUIPMENT: Oscilloscope Function Generator 555 Timer Capacitors Resistors BACKGROUND: The 555 is a versatile integrated circuit timer that it can be used in a variety of applications. Its open architecture allows to be connected as a monostable or an astable multivibrator. The internal architecture of the 555 is displayed on Figure 1. Referring to Figure 1, the basic monostable and astable modes are discussed next. A) MONOSTABLE OPERATION: The basic monostable configuration is shown in Figure 2. It can be easily shown that this time duration is given by: T p = RC ln(3) It has to be emphasized that T p has to be longer than the time which the trigger is held low, otherwise it is possible to get stray oscillations at the output. To prevent this, it is possible to convert the input from level triggered to edge triggered by adding an RC differentiator. This modification is shown in Figure 2. For this modification to be effective, it must be RC<<T p. B) ASTABLE OPERATION: The basic astable circuit is shown in Figure 3. The time duration which the output remains high and low are easily found to be given by: TH = ( RA + RB ) C ln(2) T = L RBC ln(2) It is noticed that it is impossible to have T H = T L (why?), thus we cannot exactly have a 50% duty cycle with this circuit. However, by simply using an extra diode, it is possible to modify the circuit so that a 50% duty cycle can be obtained. (How?) PREPARATION: a) For the monostable circuit of Figure 2 select values of the timing components for an output pulse width of 0.1 ms (approx.). b) For the astable circuit of Figure 3 select values of the timing components for 10 KHz frequency and 1/3 Duty Cycle. 28

29 EXPERIMENT: The purpose of the experiment is to experimentally study the operation of the 555 timer in both the monostable and astable modes. Use a power supply voltage of 12V. A) MONOSTABLE OPERATION a) Connect the 555 timer in the basic monostable circuit of Figure 2 using the timing component values you computed in the preparation part (a). Connect pin 4 (Reset) to pin to the power supply. Connect the trigger input to a square-wave alternating from 0V to 6V. b) Set the input frequency to 6 KHz. Observe on the scope both the trigger and the output voltage. Mark the triggering points. c) Change the input waveform into triangular (0 to 6V) and determine precisely the input voltage level where triggering occurs. d) Change the input waveform back to square-wave. From the oscillograms or by using the frequency counter, compare the input and output frequencies when the input frequency is 6 KHz, 18 KHz and 27 KHz. Make comments. e) Decrease the input frequency to 1 KHz. Observe carefully the output voltage and the voltage across the timing capacitor. Explain what you see. f) Modify the trigger circuit for edge triggering. You can use the modification suggested in Figure 2. Repeat part (e) and notice any differences. Observe also the trigger (at pin 2) and the output voltages. B) ASTABLE OPERATION a) Connect the astable circuit of Figure 3 using the timing component values you computed in the preparation part (b). Observe on the scope the voltages at the output pin and across the timing capacitor. Measure the extreme values of the capacitor voltage. b) Set the oscilloscope AC coupled and observe the voltage at pin 8 (power supply). Increase the oscilloscope gain. What do you see? Connect now a 10μF capacitor between pins 8 and ground. Did anything change? c) Connect a diode between pins 6 and 7 with the anode at pin 7. Observe any changes in the output waveform. Explain. d) Connect the function generator between pin 5 (control voltage) and ground (If you had a capacitor between pin 5 and ground, remove it). Set the generator at 200 Hz. Observe both the outputs of the generator and the 555. Vary the amplitude of the generator output and observe the results. Try with various waveforms. REPORT: In your report present experimental results and compare them with the expected results. Discuss any discrepancies, make comments and write conclusions. REFERENCES: Current textbook for EEL

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31 EXPERIMENT EVALUATION FORM COURSE : EEL 4309 SEMESTER: COURSE INSTRUCTOR: LAB INSTRUCTOR: EXPERIMENT: Please write comments on the following issues PART A (experiment): 1) Was the experiment successful? 2) Did the experimental results match the theory? 3) Was the material covered in the lecture? 4) Was the experiment instructive? 5) Was the lab manual clearly written PART B (facility): 1) Did all the instruments work properly? 2) Were all the needed parts available? 3) Any other problems? PART C (Lab Instructor): 1) Was the lab instructor helpful? 2) Did he/she know the experiment? 3) Was there any brief lecture in the lab? 4) Did the lab instructor know how to operate the instruments? 5) Any comments that may help the lab instructor improve? Your name (optional): Please return to your course instructor 31

32 APPENDIX Resistor and capacitor values that are normally stocked in the lab. 0.1uF 0.047uF 100pF 200pF 470pF 560pF 680pF 820pF uF 0.002uF uF uF uF uF uF 0.005uF 270pF 120pF 180pF uF 390pF uF 330pF 220pF 150pF uF 0.001uF uF 22MΩ 15MΩ 9.1MΩ 7.5MΩ 6.2MΩ 4.3MΩ 3.6MΩ 3MΩ 2.7MΩ 2.4MΩ 1.8MΩ 1.6MΩ 1.5MΩ 1.3MΩ 1.2MΩ 1.1MΩ 1.2KΩ 3.6KΩ 4.3KΩ 5.1KΩ 6.2KΩ 7.5KΩ 11KΩ 12KΩ 13KΩ 16KΩ 18KΩ 22KΩ 24KΩ 36KΩ 39KΩ 43KΩ 51KΩ 62KΩ 91KΩ 120KΩ 160KΩ 220KΩ 240KΩ 360KΩ 430KΩ 510KΩ 620KΩ 150Ω 470Ω 32

33 First the code How to read Resistor Color Codes Black Brown Red Orange Yellow Green Blue Violet Gray White How to read the code First find the tolerance band, it will typically be gold (5%) and sometimes silver (10%). Starting from the other end, identify the first band - write down the number associated with that color; in this case Blue is 6. Now 'read' the next color, here it is red so write down a '2' next to the six. (you should have '62' so far.) Now read the third or 'multiplier' band and write down that number of zeros. In this example it is two so we get '6200' or '6,200'. If the 'multiplier' band is Black (for zero) don't write any zeros down. If the 'multiplier' band is Gold move the decimal point one to the left. If the 'multiplier' band is Silver move the decimal point two places to the left. If the resistor has one more band past the tolerance band it is a quality band. Read the number as the '% Failure rate per 1000 hour' This is rated assuming full wattage being applied to the resistors. (To get better failure rates, resistors are typically specified to have twice the needed wattage dissipation that the circuit produces) 1% resistors have three bands to read digits to the left of the multiplier. They have a different temperature coefficient in order to provide the 1% tolerance. 33

34 Examples Example 1: You are given a resistor whose stripes are colored from left to right as brown, black, orange, gold. Find the resistance value. Step One: The gold stripe is on the right so go to Step Two. Step Two: The first stripe is brown which has a value of 1. The second stripe is black which has a value of 0. Therefore the first two digits of the resistance value are 10. Step Three: The third stripe is orange which means x 1,000. Step Four: The value of the resistance is found as 10 x 1000 = 10,000 ohms (10 kilohms = 10 kohms). The gold stripe means the actual value of the resistor mar vary by 5% meaning the actual value will be somewhere between 9,500 ohms and 10,500 ohms. (Since 5% of 10,000 = 0.05 x 10,000 = 500) Example 2: You are given a resistor whose stripes are colored from left to right as orange, orange, brown, silver. Find the resistance value. Step One: The silver stripe is on the right so go to Step Two. Step Two: The first stripe is orange which has a value of 3. The second stripe is orange which has a value of 3. Therefore the first two digits of the resistance value are 33. Step Three: The third stripe is brown which means x 10. Step Four: The value of the resistance is found as 33 x 10 = 330 ohms. The silver stripe means the actual value of the resistor mar vary by 10% meaning the actual value will be between 297 ohms and 363 ohms. (Since 10% of 330 = 0.10 x 330 = 33) Example 3: You are given a resistor whose stripes are colored from left to right as blue, gray, red, gold. Find the resistance value. Step One: The gold stripe is on the right so go to Step Two. Step Two: The first stripe is blue which has a value of 6. The second stripe is gray which has a value of 8. Therefore the first two digits of the resistance value are 68. Step Three: The third stripe is red which means x 100. Step Four: The value of the resistance is found as 68 x 100 = 6800 ohms (6.8 kilohms = 6.8 kohms). The gold stripe means the actual value of the resistor mar vary by 5% meaning the actual value will be somewhere between 6,460 ohms and 7,140 ohms. (Since 5% of 6,800 = 0.05 x 6,800 = 340) 34

35 LF351 Single Operational Amplifier (JFET) 35

36 LM393 Dual Differential Comparator 2

37 3

38 LM555/NE555 Single Timer 4