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 Website and original documents Copyright © 2007–2010 by Theodore P. Pavlic Licensed under a CC-BY-NC 3.0 License |
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Contents |
SOURCE CODE: LaTeX has been used to generate the documents for this class. The Mercurial repository at http://hg.tedpavlic.com/courses/osu/ece327/ archives the source code of these lab resources.
LICENSING AND REUSE: Unless otherwise expressly stated, all original material of whatever nature created by Theodore P. Pavlic and included in this website and any related pages, including its archives, is protected by copyright and licensed under a Creative Commons Attribution-Noncommercial 3.0 United States License ("CCPL"). Use of this website is expressly conditioned upon the user’s acceptance of the terms and provisions of the CCPL. Use of this site and any of the materials thereon constitutes acceptance of the CCPL by the user.
COMPONENTS:
Make sure your function generator is calibrated for high output impedance load. Look for a HIGH Z [1, 2] mode in the output settings (also called output termination). After changing this setting, go back to your waveform settings and enter the correct amplitude.
- Recall from your electromagnetics classes (e.g., ECE 311/312) that transmission lines must be terminated to prevent reflections. Conventional terminating loads are 50 ohms, which means that a function generator on one of these lines must drive a 50 ohm load. So the function generator designers have embedded a 50 ohm load as the output impedance of the scope and purposely deliver twice the desired amplitude. When connected to a 50 ohm load, the resulting voltage divider provides the right amplitude because it has a gain of 0.5.
- In our class, load impedances (e.g., inputs to amplifiers) are much higher, and so the resulting voltage divider with the 50 ohm output impedance has near unity gain. Telling the function generator about our "HIGH Z" load prevents it from doubling the output.
- NOTE: When you change to "HIGH Z" mode, the function generator will change your output setting to twice its original amplitude. You will need to readjust it.
- Keep in mind that there is always a voltage divider at the output of the function generator, and so it is always best to use your digital multimeter (DMM) or your oscilloscope to tweak the function generator’s output.
Use a 10× (or ×10 or 10:1) probe to increase the high-frequency impedance seen by the device under test (DUT).
- The capacitance of a standard 1× (or 1:1) probe creates a low-pass filter. A 10× probe adds series capacitance and resistance to compensate for this effect.
- The extra resistance of the probe is almost exactly 9× the input resistance of the scope, and so the signal on the scope is scaled by a tenth. Use the scope’s probe settings to automatically scale it to fix this.
The probe may need to be compensated. Please do not attempt this task yourself on the lab probes. However, recognize how it is done and file it away in your long-term memory for the next time you see ringing on a scope.
Most of our 10:1 probes have a small spring-loaded sense pin at their oscilloscope connection. When this pin or the scope connectors get dirty, it becomes difficult for the scope’s auto-detection features to work. Placing a small piece of paper between this pin and the scope should prevent the scope from trying to automatically change the probe settings. Cleaning these contacts may improve the situation.
Of course, the DMM may need a new battery; however, it’s usually the case that the DMM is in a cautionary mode to prevent it from being accidentally turned on.
While the DMM dial is turned to something other than "Off," press the two buttons under the display simultaneously. The DMM should "wake up" and be operable again.
To prevent the DMM from entering this mode, be sure to turn it off when you’re not using it. If the DMM is left on for a few subsequent long periods of time without much use, it will enter this sleep mode.
Use a bypass capacitor across your power rails and possibly near your circuit elements.
- Choosing the size and type of each of these can be complicated.
- A good rule of thumb is to put pretty large capacitors (e.g., multiple microFarads) at the central power rails and slightly smaller (e.g., 0.001–0.1 microfarads) on the power pins at each component.
Stray parasitic capacitance is everywhere. In fact, the pins of an IC and the air between them form a capacitor of at least a few picoFarad. If you can, try to choose circuit elements that dominate over or compensate for these strays.
If setting an RC, choose a low R to give you a high C; however, realize that the low R may result in a higher power draw from your circuit.
The Agilent oscilloscopes have an internal TRC ("Trace?") file format that are not easy to open on anything but the scopes themselves. Using the "Quick Print" button or being sure to check the "Formats" menu after clicking "Save" will let you save to more conventional formats like CSV and BMP.
If you have a bunch of TRC files, setup a time with your instructor to visit the lab. You’ll be able to use the scope to open the TRC files on your disk and then re-save them as the format you like. However, you may lose some data in the conversion process.
While it’s fine to include BMP ("BiTmaP") files in your lab report, CSV ("Comma Separated Values") files are much more versatile. Rather than storing an image, they store actual data that can be opened by Microsoft Excel or MATLAB (see the csvread command for one example of how to do this; try typing help csvread inside MATLAB). You’ll then be able to plot and manipulate the data as you wish.
When choosing resistor and capacitor values for your oscillator (e.g., when designing relaxation oscillators with a 555 timer IC), remember to dominate the stray parasitic resistances and capacitances present all over your breadboard.
Assume that the breadboard and chip pins contribute a few Ohms (even as many as ten or twenty) of resistance and a few picoFarads of capacitance to your circuit. Because of this, keep your resistances greater than a kiloOhm and your capacitances greater than 10 nanoFarad. Resistances lower than this are bad for your circuit anyway because they probably mean your burning too much power off.
Keep in mind that the above is just a rule of thumb. There are plenty of applications where large resistances (e.g., in the feedback path of operational amplifiers) are very bad things and will affect the bandwidth and stability of your circuits. Just try to anticipate the parasitics and work around them.
Your breadboard came with screw terminals for a reason. Banana plug connectors can plug into the terminals. Thus, setup your power rails by running wires from the three or four banana terminals on your board. When you’re ready, plug your power supply into the banana connectors directly. It’s much more convenient.
Unfortunately, many students throw away their banana connectors rather than attaching them. In the future, assemble your breadboards completely; they work better that way.
On the other hand, die-hard high-frequency analog prototypers will abandon breadboard use entirely for setting up "dead-bug" circuits on a bare copper ground plane. This practice, which places chips upside down making them look like dead bugs, can improve performance but is less flexible (it can require glue in some cases, and will definitely require solder). In our lab, using big enough bypass capacitors (see "Power supply noise" tip above) is the closest we’ll get to low noise prototyping.
Potentiometers are often used as two-terminal devices in this laboratory as variable resistors. Instead, try using all three terminals. A potentiometer is nothing more than a voltage divider, and the screw moves the output of the voltage divider (the middle pin) from the high voltage to the low voltage. If you need to tune a voltage divider, just use a potentiometer instead!
Keep in mind that you should probably choose a potentiometer with a size that only draws a few milliamps at most from your circuit. Even though you probably only care about the resistance ratios, you should care about the current draw (and power dissipation) as well. If not for any other reason, it will keep you from getting blisters when you touch your circuit.
There is no DC feedback through a capacitive feedback path. Additionally, every real OA has a small imbalance between its inputs that manifests itself like a small DC source connected to one of the inputs. So the integrator integrates this small offset and produces an additional ramp on the output. In other words, the infinite DC impedance of the capacitor looks like an infinite DC gain at the output, and so the OA tries to make its output have an infinite DC component after transients die out (i.e., the OA output goes to one of its rails).
One solution to this problem is to provide finite DC feedback with a large resistor (e.g., 1–10 megaOhm) in parallel with the feedback capacitor (i.e., the "Miller integrator"). Now, the small offset potential at the OA input will show itself as an amplified, yet hopefully still small, offset in the output. To reduce the amplification, the feedback resistor can be reduced. However, the smaller the feedback resistor, the greater the corner frequency of the lowpass filter you’ve just created. In other words, your circuit will look less like an integrator and more like a smoothing filter; low frequency signals will not be integrated well.
(note that some OA’s already have a large feedback resistance built into the device in order to ensure DC feedback. Capacitive leakage may also play a role. If you are noticing offset on your output rather than railing, it is most likely because there is an internal (or parasitic) large resistance in parallel with your capacitor)
Another solution is to capacitively couple your input to the integrator (i.e., place a LARGE capacitor (e.g., 1 microFarad or higher, which is probably only available polarized) in series between your signal and the integrator input). This method shifts your input signal by the offset potential, and so the offset does not generate any additional current into the capacitor. Therefore, the offset will still be present at the output, but it will not be amplified.
If you are using the integrator as a ramp generator, neither of these solutions will work. Because you are probably feeding a constant (i.e., DC) signal to the input of the integrator, you would not want to amplify DC nor capacitively couple your input. Therefore, your only solution is to put the OA back into balance. The most general balancing method is to use the inverting input as a sum junction. Tie the outer legs of a potentiometer (e.g., a 10 kiloOhm) to your positive and negative rails. Tie the inner "wiper" to the inverting input of the OA. With the input of your integrator tied to 0 (or shorted to the non-inverting input of the OA), tune the potentiometer until the output is zero.
Most OA’s have "balance" pins that can be used to null the offset in a similar fashion. The usual procedure again involves a potentiometer. Tie the outer legs of the pot to the two balance pins, and tie the wiper to the negative rail. Short the inputs of the OA together, and adjust the pot wiper until zero appears on the output.
Keep in mind that OA offset varies with temperature and can drift with time. One of the reasons why electronics are "burned in" at the factory is to reduce the rate of drift (here, voltage references come to mind). Therefore, nulling offset is a much more complicated problem in a product that has a lifetime longer than one class time. In our case, if we’re not using the integrator for a ramp generator, we should probably null the offset and do one of the other methods (i.e., capacitively couple the input signal or add a large feedback resistor).
Make sure that you didn’t swap your collector and emitter (i.e., make sure you don’t have your transistor plugged in backwards).
Take a look at the "Arrangement of n-Doped and p-Doped Regions" in Figure 1.2 of the lab text. As you can see, the only difference between the emitter and the collector are the "size." The base–emitter diode is "small" and the base–collector diode is "large." As a consequence, a transistor "works" when emitter and collector are reversed, but the current gain will be very low (e.g., the collector current might be equal to the base current). Our models of a transistor assume that the current gain is relatively infinite, and so they will poorly predict how a circuit will work in the other case.
Because of the "size" of the base–emitter diode, it is easy to reach the reverse breakdown voltage of the base–emitter diode if it is connected improperly. So hooking a transistor up "backwards" can either damage the transistor or simply produce a poorly performing circuit.
Great reference for advanced students. Classic electronics reference. Highly respected. The [analog] electronics bible.
Standard microelectronics text. More focus on younger undergraduate student audience. Lots of details, but very little breadth. Poor reference for advanced students. In fact, so many details are given that the text can be a poor reference for novices as well.
This website presents lengthy discussions of circuits for beginners. The discussions are interesting and include helpful animations that treat electric potential like fluid flowing into and out of resistors. There are also sections that are meant to be displayed on a whiteboard, and so those pages read like lectures.
There are too many good pages to list here. You may want to start looking at the master index of circuits ("circuit stories").
This webpage is a treasure trove of useful circuit information.
Engineers are not scientists in the traditional sense. Scientists generate knowledge about the natural world by observing natural phenomena (in fact, the word "science" comes from the Latin for "knowledge" or "knowing"). Engineers use that knowledge to generate new technologies that aid in human activities, but they are rarely concerned with generating new knowledge about the natural world. Instead, engineers generate knowledge about their own creations. While the subject matter is different, the method behind the generation of knowledge is identical. That is, engineers are "technoscientists"; they use the scientific method to generate knowledge about technology.
In the engineering laboratory, you should practice all of the steps of the scientific method. In particular,
These steps should influence everything you do in the lab and everything you write in your report.
- Define the question (e.g., "How does a certain filter respond to a generic input signal?")
- Gather information and resources (e.g., recall your operational amplifier theory and the physical characteristics of passive electronic devices)
- Form hypothesis (e.g., "The filter will act like an abstract linear time-invariant system with transfer function H(s).")
- Perform experiment and collect data (e.g., measure magnitude and phase response at several frequencies)
- Analyze data (e.g., plot the data)
- Interpret data and draw conclusions that serve as starting point for new hypothesis (e.g., compare measured and expected responses and draw the conclusion that the theoretical model matches the qualitative low-pass behavior of the system but matches poorly in the neighborhood of the corner frequency. Suggest that cable resistance or component tolerances may have changed the effective corner frequency. Suggest a new experiment that measures cable resistance and repeats trials over several components with tight tolerances)
- Publish results (e.g., submit your lab report)
- Retest (e.g., assume that others will read and respond to your published report by following your suggestions for future work)
A good section structure inspired by the scientific method is:Alternatively, the conclusions section could be called an "Analysis" section and a new "Conclusions" section could be added that summarizes the report. The section structure you choose should help reinforce the message you are communicating in your report; keep the steps of the scientific method in mind.
- Introduction – the purpose of the lab (i.e., define the questions that you are trying to answer during the experience)
- Procedure – what was done (i.e., describe the experimental method)
- Theoretical results – what was expected (e.g., your hypothesis would fit nicely here)
- Measured results – what was observed (i.e., present your data without drawing conclusions)
- Conclusions – explanation of measured results and suggestions for future work
- Interpret the data to show how it responds to the relevant questions of the experience – use the data to test your hypothesis.
- Suggest starting points for new hypotheses that explain the observed differences from the theoretical results – if possible, suggest new experiments to test these new hypotheses.
For the lab reports you submit to me, you do not need an abstract nor any appendices. All material should be in-line with the text of the document.
Regardless of your section choices, be sure to pay attention to the course policies on lab reports (e.g., include a cover page with table number, group member names, my name, section, etc.).
Reports should be written from the following point of view: the reader is knowledgeable on the subject of electronics but knows little of your project. You must, therefore, explain your project in the most organized, economical fashion possible. This is good practice as this will, most likely, be the point of view for your monthly/quarterly/yearly reports in industry. This neatness and readability of your report is a significant factor as well as the actual contents. You should try to explain to the reader how the different parts of this circuit work in a clear and organized fashion.
For myriad reasons, professional technical documents are rarely produced with popular programs like Microsoft Word. In areas that are highly influenced by mathematics (e.g., engineering), the free TeX typesetting system dominates. Many TeX (pronounced "tech") users prefer the LaTeX suite of macros to simplify common typesetting tasks.
TeX documents, like the source code for computer programs, start as text files that are later "compiled" into their final document form. A typical TeX workflow is
- Edit document source code in a standard or specialized text editor. For example, a text file called "mydocument.tex" could contain the LaTeX code:
\documentclass{article} \begin{document} \textbf{Hello world!} \end{document}- "Compile" source code to produce printable document. The "mydocument.tex" file would produce a "mydocument.pdf" that would contain the bold text:
Hello world!A good editor will typically provide a quick way (e.g., a "LaTeX" button on the graphical user interface) to compile your code.
If you want to compile your code manually, you can use PDFLaTeX with the commandpdflatex mydocument.texor you can use LaTeX with the commandslatex mydocument.texThe difference between these two methods has an impact on what type of figures you can include (i.e., EPS files versus PDF, GIF, JPG, or PNG files). See below for details.
dvips mydocument.dvi
ps2pdf mydocument.ps
- View printable document and repeat process to make changes (e.g., you could change the \textbf{Hello world!} line to be simply Hello world! to get rid of the bold).
Thus, many people feel that TeX typesetting is more like programming than it is like using standard word processing tools. So it’s not surprising that you’ll need a "compiler", editor, and viewer (note: the ECE computer labs are already equipped with everything you need to get started).
\usepackage{caption}
\usepackage{graphicx}
Then, in the main part of your document, you can
choose whether to include your graphics as
"floats" or not. Most figures in books are
"floats." That is, they do not appear exactly where they are
mentioned in the text. Instead, they "float" to a convenient
place (e.g., the top of the next page). In lab reports, people
sometimes prefer that their graphics do not float.
\begin{figure}
\includegraphics[width=0.5\columnwidth]{my_graphics_file.png}
\caption{A nice caption for my figure.}
\label{fig:a_unique_fig_label}
\end{figure}
Alternatively, if you want the figure to be
typeset EXACTLY where you place it within your source code, use
lines like
\begin{center}
\includegraphics[width=0.5\columnwidth]{my_graphics_file.png}
\captionof{figure}{A nice caption for my figure.}
\label{fig:a_unique_fig_label}
\end{center}
That is, replace the figure
environment with a center environment and
replace the \caption line with a
\captionof{figure} line.
- Daily quizzes: 20%
- Lab reports: 40%
- Lab clean-up: 10%
- Final exam: 30%
At instructor’s discretion, grades may be made available on Carmen.
- Each week, there will be a quiz at the beginning of class over the material in that day’s lab (i.e., a pre-lab quiz).
- Quizzes are closed book and closed notes.
- Only a short time at the beginning of class will be allocated for quizzes, and so students should avoid being late to class.
- The final exam will be a written test over theory discussed in the class.
- There will be no hands-on laboratory component to the final exam.
- Students are required to attend all labs.
- Students will work in groups of two or three.
- Each group should prepare a floppy disk to store data from the oscilloscope. The data can be saved using the oscilloscope’s print to disk feature.
- See the lab report writing resources for more information about the contents of a good lab report.
- Each group will submit one lab report.
- On your cover page, include:
- the class identifier (i.e., "ECE 327")
- the section day and time (e.g., "Tuesday 8:30")
- instructor name (e.g., "Instructor: Jane Engineer")
- names of all members of group (grades are given to these members)
- your table number from label on power supply mounted adjacent to table
- Lab reports must be typed and pages must be numbered.
- If you must use hand-drawn figures or hand-written calculations, use engineering graph paper. Include them either as attachments to the end of the report or paste or photocopy them into the body of the report.
- Tables and figures should be numbered and have descriptive captions. Because these items naturally float to the best location on the page, they should be referred to by their name and not be their relative position (e.g., refer to "Table 1" and not "the table below").
- Lab reports are due at the beginning of the next lab session and will be penalized 10% per day late.
- Lab report grading (instructor policy takes precedence):
- Lab work (30%) – evidence of having successfully completed the lab tasks.
- Figures/Tables/Equations (20%) – the main technical details of the report
- Discussion (50%) – usually divided (depending on lab) into:
- Purpose – the purpose of the lab
- Procedures – how the lab was done
- Theoretical results – expected results
- Measurement results – actual results
- Conclusions – explanation of actual results
- Again, see the lab report writing resources for more information about the contents of a good lab report.
Students must attend all labs. If a lab needs to be missed, arrangements should be made with the instructor at least 24 hours prior to the lab so that the lab work can be made up. The instructor reserves the right to determine when make-up work is allowed. Students are responsible for all assignments, change of assignments, announcements, and other course-related materials.
Late lab reports will not be accepted unless prior (i.e., at least 24 hours in advance) arrangements have been made with the instructor.
While groups may work together outside of class when deciphering their results, all handed-in material must be unique. That is, each group should actually compose their lab reports separately, and there is no time when individuals can collaborate on quizzes or exams.
Any written material turned in to me (lab reports, quizzes, exams, etc.) falls under the purview of the University and the ECE Honor System rules. If a lab report does not represent a group’s understanding of the material or a quiz or exam does not represent an individual’s understanding of the material, it will be considered to be an honor code violation. In these cases, the incident must be reported to the ECE department.
Students with disabilities that have been certified by the Office for Disability Services will be appropriately accommodated and should inform the instructor as soon as possible of their needs.The Office for Disability Services
150 Pomerene Hall
1760 Neil Avenue
Telephone: 614-292-3307, TDD: 614-292-0901
http://www.ods.osu.edu/
Course supervisor: Professor Steven B. BibykCatalog Description:
Transistor characteristics, large and small signal parameters, transistor bias and amplifier circuits, operational amplifiers, logic circuits, waveform generation.
Course Prerequisities: 209
Course Prerequisities or Concurring: 323Courses that require 327 as prerequisite: 628
Prerequisites by Topic:
Circuit theory; ability to use LINCAD (Linear Computer-Aided Design)Course Objectives:
- Relate large and small-signal models of diodes, JFETs, MOSFETs, bipolar transistors and operational amplifiers to their behavior in practical electronic circuits. (Criterion 3(a))
- Use knowledge of electronic circuits to design electronic circuits, and predict and measure performance of electronic circuits. (Criteria 3(b),(c))
- Learn the relationships between models of circuit components and their performance. (Criterion 3(a))
- Provide the student with the experience of designing, constructing, integrating, testing and debugging an active electronic circuit. (Criteria 3(c),(e))
Topics and (# of Lectures)
- Bipolar Junction Transistor (1)
- Field Effect Transistor (1)
- Voltage Regulators (1)
- Oscillator (1)
- Analog-to-Digital Conversion (1)
- Digital-to-Analog Conversion (1)
- Project Construction/Integration/Debug (3)
- Project Demonstration (1)
Class Meeting Pattern
- 1 48-minute class
- 1 3-hour lab
Good to take before this course: ECE 205, ECE 206, ECE 209, ECE 301, ECE 323
Good to take after this course: ECE 620, ECE 628
Good to take if you like labs like this (i.e., practical experience working toward a lab project): ECE 667
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Website and original documents Copyright © 2007–2010 by Theodore P. Pavlic Licensed under a CC-BY-NC 3.0 License |
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