University of Minnesota

Department of Electrical and Computer Engineering

EE 2002 Laboratory Manual

An Introductory Circuits/Electronics Laboratory Course

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Introduction You will find this laboratory to be different than those you have experienced up to this time. It was designed with several objectives in mind. First, it is intended to supplement the lecture course EE2001 and can only be carried out with the maximum benefit if you are acquainted with the topics being discussed there. Second, it is intended to develop your self-confidence in laboratory procedures and in drawing conclusions from observations. As a consequence the instructions are very spare and assume you will be able to extract conclusions from each experiment and will relate parts of the total lab to each other without being explicitly asked to do so. Important Points - Your grade in this course will depend principally on your in-lab work. - You are expected to maintain a lab notebook. It must contain a running account of the experiment. It is not intended to be a book into which you copy notes previously gathered on the back of an envelope. It must however be legible and coherent. Write in such a way that another person could perform the same experiment based on your account, and this same person could understand the conclusions that you drew from your data. It is not necessary to hide your mistakes. If you make a mistake in an entry simply draw a line through that entry and start over - you will not be penalized for this. - The lab notebook should have the following characteristics: - It should be a bound notebook (spiral bound is OK). - Lab entries should be dated, and should include: - Complete circuit diagrams. - Explanation of circuit, methods, procedures, etc. - All calculations for designs. - All measurements (including component values). - All analysis and comparisons of data with theory. - Homework - There is no formal lab homework or pre-lab work in this course, but it will pay great

dividends for you to make a careful reading of the experiment description before arriving in the laboratory. You will also note that some parts of the "experiments" involve analytical work which can be better done elsewhere. Most problems students have with this course are due to lack of preparation prior to coming to lab. If after reading through the lab and consulting the relevant section of your EE2001 text you do not understand something, seek out either your TA or the faculty member in charge of the lab.

- If you do not spend at least 30 to 40 minutes studying the experiment, making notes, circuit

diagrams, calculations, etc. in your laboratory notebook, prior to coming into the lab, you will not finish the experiments. It will be obvious to everyone in the class, including your

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classmates, your Teaching Assistant, and your professor, that you have come in unprepared. And you will receive no extra help for such poor performance.

- MILESTONES. - In each experiment there will be a few “milestones”. These are specific tasks which must be

accomplished and demonstrated to the TA or professor before going on to the next item. All milestones must be completed or you will not pass the course. If the milestones are not completed by the end of the quarter you will receive an F for the course. While the milestones are not a part of the grade formula, delays in milestone completion will unavoidably delay the submission of your lab notebook with the corresponding grade penalty. Lab notebooks and lab reports will not be accepted if the milestones for the corresponding lab have not been completed.

- Grades Grades will be determined from the following components of the course:

Lab Notebooks - 30% Lab Practical Exams - 40% Take them seriously, they are forty minutes to one hour

in duration and they account for a significant portion of your final grade.

Lab Reports - 30% Lab notebooks will be collected up to three times during the quarter. They will be due at 4:30 PM three working days after the scheduled completion date of a lab. Lab reports will be collected one week after scheduled completion of the corresponding lab. You will be given a schedule during the first week of class which will contain all lab practical exam dates and notebook and lab report due dates.

- Late Penalties. The penalties for late notebooks or lab reports are as follows:

1 or 2 days late: 3% deducted from your FINAL SCORE. 3 or 4 days late - an additional 3% deducted from your FINAL SCORE. and so on...

Check the class website for a separate handout detailing the requirements for the lab reports. - Housekeeping Requirements. No food or drink to is be brought into the lab and most especially is not to be placed on the lab benches. At the conclusion of each laboratory session, all cables, etc. are to be returned to the proper wire racks and any borrowed equipment (there should be no borrowed equipment without the approval of the TA) returned to its proper location. The only items on the lab bench when you leave should be the equipment normally found on each bench. The TA will record a demerit

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against your record in his gradebook each time you fail to meet the above standards. Four or more demerits at the end of the term after grades have been computed will result in grade reduction of one level (A to A-, A- to B+, etc.). If for some reason, you find the lab bench does not meet the above standards when you first come in, inform your TA immediately. You are still responsible for leaving the lab bench neat when you leave.

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Experiment #1: Introduction to Lab Procedures & Equipment

Familiarization Sessions 1 and 2 Introduction The lab instructor will go over the procedures and expectations for this course. He will then demonstrate the use of the computer controlled PXI-buss based digital multimeter (DMM), oscilloscope, function generator, dc power supply, and how to wire circuits on the protoboard in each student lab kit. The student should then spend the rest of the lab period trying out the equipment to become more familiar with it. Measurements 1. Connect the 6V dc supply terminals from the DC power supply to the PXI-based DMM and the stand-alone DMM as shown in Fig. 1-1. Vary the setting of the dc output and compare with the reading of the DMMs. Be sure that the DMMs are set to read DC volts.

Figure 1-1. Connection of dc power supply and digital multimeters (DMMs) for

measuring dc voltage. 2. Repeat step #1 for the 0 to +20 supply and then the 0 to -20 supply. 3. Display a 4 V peak-to-peak sinewave at a frequency of 1 kHz on the oscilloscope. Connect the function generator to the oscilloscope as shown in Fig.1- 2 to obtain the display. Adjust both the vertical sensitivity (volts per division) and horizontal (time base) sensitivity (seconds, milliseconds, microseconds) to obtain a good display showing two or three cycles of the waveform.

Figure 1- 2. Connection of function generator to oscilloscope for displaying

and measuring ac waveforms. The connection of the DMM to measure rms

voltages is also shown. 4. Measure the amplitude of this ac waveform with the DMM set on the ac voltage mode. Compare this reading with the base-to-peak value you observe on the oscilloscope. The voltage measurements in steps #3 and step #4 should have different values. The DMM is calibrated to display the rms value of a sinewave which equals 0.707 of the base-to-peak value of a sinewave.

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Other waveforms such as square waves and triangular waves will have different rms-to-base-to-peak ratios as measurements of step #5 will illustrate. 5, Repeat steps #3 and #4 with square waves and then triangle waves. A square wave has an rms value which is equal to the base-to-peak value. A triangle wave has an rms value value which is 0.578 of the base-to-peak value. . 6. Construct the circuit shown below in Fig. 1-3, sometimes termed a voltage divider. Use a 4 V peak-to-peak 1 kHz sinewave for the input and measure the output voltage with the oscilloscope and DMM. The point of this step is to become familiar with using the protoboard to construct circuits and make connections to sources and measurement instruments. Examine the layout of the protoboard shown below in Fig. 1-4 and note that a specific column of component insertion holes are shorted together. Each individual terminal of a component should be inserted into a separate column as illustrated for a resistor unless it is desired to have terminals shorted together. Electrical connections to the function generator and oscilloscope are made via so-called BNC connector terminals. The outer cases of these connectors are directly connected to the ground (ground pin) of the ac power plug. When these instruments are connected to the AC power outlets, all of the instruments grounds (BNC outer cases) are shorted together as indicated in the figure. Any instrument that connects to the AC power system is configured in this manner (for reasons of safety). Thus it is not possible to connect the oscilloscope so

as to measure the voltage across the 4 kΩ resistor because the 1 kΩ resistor would then be shorted out.

Fig. 1-3. Voltage divider circuit and

instrument grounding.

Fig. 1-4. Diagram of protoboard which is used to construct circuits for laboratory

measurements.

7. Replace the function generator with the 0-6V dc power supply and repeat step #6. 8. Construct the circuit of Fig. 1-5. Set the DMM to measure dc currents. In this configuration the DMM is being used to measure current.

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Figure 1-5. Circuit arrangement for

measuring current through a resistor.

Compare the current measured by the DMM with the current output indicated by the dc power supply display. They should be the same. 9. Construct the circuit of Fig. 1-6 and use it to measure the resistance of several of the resistors in your lab kit. Make sure to use the proper set of terminals on the DMM and set the DMM to measure resistance.

Figure 1-6. Circuit for determining values of resistors.

Compare the reading of the DMM with the value of resistance indicated by the color code on the resistor body.

Experiment #2: DC Measurements Sessions #3 and #4 Experiments 1. Measure the voltage of a nominal 1.5v AAA cell to the nearest millivolt.

2. Determine experimentally the value of resistor that, when place across the cell, will make a measurable change in the measured cell voltage. Calculate the internal resistance of the cell. 3. Measure the voltage range of each of the power supply outputs. A later experiment will require a voltage which can be adjusted over the range 0 to 40v. Decide how you would provide such a voltage. 4. Set a power supply output to the value of the cell voltage measured in item 1. Determine the change in this voltage when the supply is loaded with the resistor used in item 2. 5. Design a circuit to light the red light-emitting diode (LED). The LED current must be about 15 ma (no more!). The diode voltage will be about 1v but you must not connect a voltage source directly to the diode because the current is a very strong function of this voltage and chances are that the diode current would exceed the maximum allowed. NOTE: The short lead of the diode is the cathode, i.e. the negative lead. _________________________________MILESTONE #2-1: Demonstrate your LED circuit to your instructor, making sure that meters are connected to show diode current and voltage and that there is no possibility of exceeding the specified maximum diode current. __________________________________ Demonstration The instructor will demonstrate the use of the oscilloscope to measure periodic waveforms and to display one variable versus another. The signal generator will also be demonstrated.

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Experiments 6. Connect a voltage divider to an output of the power supply. Design it to give an output that is 1/3 of the supply voltage and so that neither the power ratings of the resistors nor the current rating of the supply are exceeded. The voltage output of the divider must not change by more then 1% when loaded with 10KΩ. 7. Design a current divider that will provide a 1/3 - 2/3 current split. Observe the current and power limitations as you did in the previous item. Another design constraint is that the current meters inserted to measure the current division ratio must not upset this ratio. __________________________________ MILESTONE #2-2: Demonstrate your current divider. Show that the current meters have no effect on the current division. __________________________________ 8. Construct a non-trivial resistive circuit with at least 2 loops and at least 3 resistors in each loop. Verify Kirchhoff's laws for this circuit. Notice that this item is more "open ended", i.e. there is more room for individual initiative. These lab instructions will be increasingly presented in this mode. __________________________________ MILESTONE #2-3: Demonstrate your working circuit. Be prepared to show one or two branch voltages and how they compare to those calculated in your notes. __________________________________

Experiment #3: Circuit Theorems

Session #5 Experiments 1. Construct a resistive circuit containing series and parallel branches and a DC

voltage source. Measure the voltage at at least 2 nodes (relative to a reference node) as a function of the source voltage. Measure the current in at least 2 branches as a function of the source voltage. 2. Construct the circuit shown below. It will be necessary to use a separate dc power supply in place of the PXI-based dc power supply because the PXI dc supply does not have three isolated dc supplies. Your lab instructor will provide the required triple output isolated dc supply.

Verify the superposition theorem for at least 2 nodes and 2 branches. 3. Design and construct another resistive network containing 3 voltage sources. Determine selected node voltages and branch currents analytically and experimentally. 4. Construct the circuit shown below. .

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Determine, experimentally and analytically. the Thevenin equivalent at the port shown. __________________________________ MILESTONE #3-1: Explain to your instructor how you carried out item 4.

Experiment #4: I-V Curves and Load

Lines

Session #6 Demonstration The instructor will demonstrate the small signal resistance versus dc current level for a diode and will discuss the load line method. Experiments 1. Measure the current vs. voltage relation of the incandescent lamp supplied. 2. Using your data from item 1 and the load line approach, determine the lamp current expected for the following values of power supply voltage and series resistor. Voltage Resistance 40.0 4000 Ω 20.0 2000 Ω 3. Check the results of item 2 by direct measurement. 4. Build this circuit and, driving it with the signal generator, display on the scope the output voltage versus the input voltage.

5. Change the circuit so that it limits for negative input voltages. 6. Change the circuit so that it limits at +2 v. 7. Change the circuit so that it limits at +2v and also at -2v. __________________________________ MILESTONE #4-1: Demonstrate your circuit of item 7. __________________________________ 8. Show the influence of your circuit of item 7 on various input periodic waveforms.

Quiz #1 on Exps. #1, 2, and 3 Session #7

Experiment #5: Diodes & Rectification Session #8 . Experiments 1. Measure the current-voltage relation for the 1N4740 diode over its entire allowable ranges of voltage and current. Obtain a collection of data points. 2. Use the data of item 1 to determine the small signal resistance of the diode at forward currents of 10, 20 and 30 ma. 3. Devise a large-signal model for your Zener diode, applicable in the reverse breakdown region for currents from 10 to 50 ma.

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4. Repeat the forward bias measurements of step 1 using the DiodeIV and use the saved data to repeat step 2. Compare with the manually acquired results. 5. Examine the output of this circuit for 1 KHz sinusoidal input amplitudes from 0.5 to 5v.

6. Investigate the following power supply circuit (known as a “bridge” circuit).

Note: The output is floating with respect to ground (i.e. both ends of the output are off of ground). Hence a single scope channel cannot be put across the load. Instead both

channels of the scope must be set up as shown. The polarity of Ch 1 should be inverted with respect to Ch 0. Both channels must have the same V/cm setting and both reference levels (zero voltage lines) must lie on top of each other. When the scope is set up in this manner, it is acting as a so-called pseudo-differential input. Trigger the scope from Ch 0. 7. Determine the effect of placing a large capacitor across the load of the circuit of item 6. Make sure you observe the proper polarity when connecting the capacitor. __________________________________ MILESTONE #5-1: Demonstrate the load voltage of the circuit of item 6, with and without the “filter” capacitor. __________________________________ Experiment #6: BJT Characteristics and Amplifiers Sessions #9 and #10 _Demonstration – session #9 The instructor will demonstrate various methods of biasing bipolar junction transistors. He will also demonstrate the use of a LabView VI (found in the UofMNIV folder) entitled BJTIV which automates the measurements of BJT output characteristics (collector current as a function of collector-emitter voltage with base current as a parameter). Experiments 1. Use the BJTIV to measure the 2N3904 collector current versus collector-emitter voltage for several fixed values of base current. __________________________________

Demonstration

The measurements in steps 1 and 2 were point-by-point manual measurements. These measurements can be automated using the PXI equipment run under the control of a LabView VI (virtual instrument) entitled DiodeIV which is found in the UofMNIV folder. Your lab instructor will demonstrate the use of this virtual instrument.

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MILESTONE #6-1: Show your setup using the BJTIV to your instructor before making any measurements. _________________________________ 2. From the data obtained calculate the small-signal common-emitter current gain at different values of collector-emitter voltage. Also calculate the small-signal output resistance at several values of collector current. __________________________________ MILESTONE #6-2: Report the values in item 2 to your instructor and explain how they were obtained. __________________________________ Demonstration – session #10 The instructor will demonstrate BJT amplifier circuits. Experiments 3. Using the techniques of the demonstration, design a circuit to measure the small-signal ac common-emitter current gain and the small-signal input resistance of the 2N3904. Make the measusrements at 1 kHz. Make those measurements at several levels of dc collector current. __________________________________ MILESTONE #6-3: Collect your values from items 2 and item 3 into a table and show them to your instructor. Demonstrate your circuit design of item 3. __________________________________ 4. Build the circuit shown, drive it with a triangular wave, and display the output voltage versus the input voltage for an input swing sufficient to cutoff the device at one extreme and saturate it at the other. Determine the common-emitter current gain and the collector-emitter saturation voltage.

5. Design and build an arrangement to switch an LED on and off at 5 Hz. The diode current should be about 20 ma when on. Do not draw more than 1 ma from the signal generator. __________________________________ MILESTONE #6-4: Demonstrate the circuit of item 7 to your instructor. 6. For the “current mirror” shown in the diagram below, determine the ratio of Ic1 to Ic2 for Ic1 ranging between 1 and 10 ma. First do these measurements for R=0, then for R=1 KΩ. (Q1 and Q2 are 2N3904)

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Experiment #7: MOSFET Characteristics and Amplifiers

Sessions #11 and #12 Demonstration – session #11 The instructor will demonstrate the use of a LabView VI (found in the UofMNIV folder) entitled FETV which automates the measurements of FET output characteristics (drain current as a function of drain-source voltage with gate-source voltage as a parameter). Experiments The experiments below all involve measurements on a MOSFET. You will use the MOSFETs contained on the 74C04 hex inverter chip. The diagram for one of the 6 inverters is shown below.

1. Use the FETVI to measure ID versus VDS for various values of VGS. Do this for one n-channel and one p-channel device. Determine the transconductance of each device at several drain current levels. The drain-source voltage should go to at least 10V to insure the devices go into the active (saturation) region.

2. Determine the threshold voltage of one n-channel and one p-channel device. __________________________________ MILESTONE #7-1: Explain to your instructor how you deduced the threshold voltages. __________________________________ 3. Use the data of item 1 to determine the conductance parameters (K) for the 2 devices. Using a reasonable value of carrier mobility, determine the oxide thickness for the 2 devices. 4. Determine the channel length modulation parameter (λ) for the n-channel MOSFET using the data from step 1. Demonstration – session #11 The instructor will demonstrate some methods of biasing FET’s. Experiments 5. Design circuit arrangement(s) to measure the ac small-signal transconductance and the small-signal output resistance for one of the n-channel devices. Make the measurements at 1 kHz and at several values of dc drain current. __________________________________ MILESTONE #7-2: Before taking any measurements, explain the circuit to your instructor. __________________________________ 6. Design a MOSFET current mirror using p-channel devices. __________________________________ MILESTONE #7-3: Demonstrate your design to your instructor.

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Quiz #2 (Exps. 1-6) Session #13

Experiment #8: Op Amps

Session #14 Demonstration Your instructor will demonstrate some applications of operational amplifiers. Experiments 1. To ensure that the output of the amplifier is zero when the differential input is zero ("offset nulling") the scheme shown

is used. (The potentiometer is adjusted to force the output to zero when the input terminals are both zero.) Design and construct a non-inverting amplifier with a voltage gain of approximately 10, null its offset and measure the gain over the complete range of input voltages. 2. Power the opamp with +5 and -5v supplies and monitor its output when one input is grounded and the other varied a few millivolts on either side of zero. 3. Repeat with the roles of the input terminals interchanged. 4. Design and construct a circuit which will indicate whether an unknown voltage is greater than or less than a given

reference voltage. The latter should be capable of being varied between -5 and +5 volts. __________________________________ MILESTONE #8-1: Demonstrate how your circuit can convert a sine wave to a square wave with a variable duty cycle. __________________________________ 5. To your comparator circuit of item 4 add green and red LED's so that the green lights up when the input voltage is less than the reference and the red when it is greater. 6. Using resistors in the few KΩ range, design a voltage divider to provide an output of about 5v from a 15v source. 7. Determine the load on the divider which will drop the output voltage to 75% of the no load value. 8. Construct a 741 buffer (unity gain, non-inverting amplifier) to insert between the output of the divider and the load determined in item 7. 9. The thermocouple is a device commonly used to measure temperature differences. Design an opamp interface between your thermocouple and the DVOM such that the DVOM reads directly in degrees F. (For example, 1 mv per degree F) Measure the temperature of various objects in the room. 10. Design and implement an arrangement which will indicate with LED's whether a temperature is above or below room temperature. __________________________________ MILESTONE #8-2: Demonstrate your circuit to your instructor and explain its operation. __________________________________