SEL EXHIBIT NO. 2031
`
`INNOLUX CORP. V. PATENT OF SEMICONDUCTOR ENERGY
`
`LABORATORY CO., LTD.
`SEL EXHIBIT NO. 2031
`
`INNOLUX CORP. V. PATENT OF SEMICONDUCTOR ENERGY
`
`LABORATORY CO., LTD.
`I PR201 3-00066
`
`I PR201 3-00066
`
`

`

`2006-2473: A NEW INTRODUCTORY COURSE ON SIGNALS, CIRCUITS AND
`SYSTEMS
`
`Mehmet Oaturk, North Carolina State University
`Mehmet C. Ozturk received the B.S. degree in Electrical Engineering in 1980 from Bogazici
`University in Istanbul, Turkey. He taught Physics to seniors at the English High School in
`lstanbul for one year while he attended graduate classes in his University. 1-le continued his
`graduate work at Michigan Technological University where he received the MS. degree in in
`Electrical Engineering under Mark G. Thompson with a thesis on hydrogenated amorphous
`silicon solar cells in 1983. He completed his doctoral studies at North Carolina State University in
`1988 under Jimmie J. Wortman. His Ph.D. dissertation was on germanium prearnorphizication and
`rapid thermal annealing for formation of ultra-shallow source/drainjunctions. After graduation,
`he joined the faculty at North Carolina State University where he is now a Professor of Electrical
`and Computer Engineering. He became a presidential faculty fellow in 1995. Dr. Ozturlc authored
`over I00 papers in journals and conference proceedings and holds 8 US patents. His current
`research interests center around advanced processes for new silicon based nancelectronic devices,
`and innovations in undergraduate education in Electrical and Computer Engineering.
`
`Michael Escuti, North Carolina State University
`Michael Escuti received the BS degree in Electrical and Computer Engineering from Drexel
`University in 1997. He continued his studies at Brown University receiving his MS and and PhD
`degrees both in Electrical Engineering in 1999 and 2002 respectively. His PhD research at Brown
`University on organic electro-optical materials and their use in photonies and flat panel displays
`has been recognized by the International Liquid Crystal Society with the Glenn H. Brown award
`in 2004 and by the Optical Society of America with the OSA/New Focus student award at the
`CLEO/QELS conference. After graduation, he spent two years with the functional polymers
`group at Eindhoven University of Technology as a post-doctoral fellow. He joined NC State
`University in 2004 as an assistant professor of Electrical and Computer Engineering where he
`continues to pursue interdieiplinary research topics in photonics, organic electronics, optics,
`biophotonics and flat panel displays.
`
`® American Society for Engineering Education, 2006
`
`

`

`A NEW INTRODUCTORY COURSE ON SIGNALS, CIRCUITS
`AND SYSTEMS
`
`INTRODUCTION
`In this paper, we present a new sophomore level Electrical and Computer Engineering (ECE)
`course on introductory concepts in signals, circuits and systems. This is the first required ECE
`course that ECE majors take after they complete the required courses common to all engineering
`students during their first year in the college. This course is a prerequisite for two other required
`core courses offered during the second semester of the second year: a course on electric circuits
`and another course on mathematical foundations of electrical and computer engineering. The
`new course was first offered in Fall 2000 semester. Since then, the course contents were
`periodically reviewed and revised based on the results of the course instructors’ assessment
`studies on student learning, discussions with the instructors of the follow-up courses and student
`feedback surveys.
`
`BRIEF HISTORY OF THE COURSE
`
`The new course is the result of an evolutionary process, which started as a one-semester course
`to introduce different specialization areas in electrical and computer engineering. The need for
`such a course came about as a result of a new EOE curriculum, which emphasized junior and
`senior level elective courses to achieve depth in at least one of the ECE specialization areas. The
`new course was intended as a catalyst encouraging the students to consider their interests in
`different ECE specializations as early as possible to help them in choosing their elective courses.
`
`At the time, the ECE faculty participating in the development effort for this course was strongly
`against creating just a survey course, which would most likely lack the rigor of a typical
`introductory course. A consensus was reached to create a course with a strong hardware
`laboratory component reviewing different ECE specializations while providing key fundamental
`concepts. It was decided to devote approximately one third of the course to introductory material
`followed by eight weeks on different specialization areas. According to the initial plan, two 75
`minute lectures per week would he used to cover the theoretical material necessary to perform
`the experiments in laboratory, which would meet ahnost every week for three hours. The
`specializations to be included in the course were decided on based on the strengths of our
`department. The list included circuits, electric power, communication, digital signal processing,
`solid state electronics, logic design, computer architecture and computer networking.
`
`One of the great challenges of this plan was to create the hardware laboratory: the experiments
`had to be representative of the respective specialization areas and they had to be chosen from
`exciting real-life applications. This approach required dedicated laboratory hardware to be
`designed and constructed in order to be able to demonstrate complex applications at a level that
`would be accessible to beginning students.
`In addition, a new textbook had to be written since
`none of the existing textbooks would fit the course contents. This job was assumed by several
`faculty members representing different specializations.
`
`Soon after we began offering the course, we began to realize that the initial plan was too
`ambitious for a one-semester course. According to the results of the student surveys, the
`students enjoyed learning about different specializations, which gave them a better understanding
`
`

`

`of their chosen professions, however, they felt rushed throughout the semester and they were not
`able to retain the material, which affected their morale and level of confidence. In the
`laboratory, we have found that a few introductory experiments were not sufficient to cover the
`basics. Furthermore, learning to operate the standard bench-top equipment, which included a
`multimeter, an oscilloscope, a function generator and a power supply took much more time than
`we originally anticipated. It was clear that the students needed extra time and support in the
`beginning of the semester. Even though the students were able to follow the step—by-step
`instructions to run the specialization experiments they were unable to enjoy and benefit from
`them because they were still busy catching up with the basics.
`
`After the first two years, it was clear that we had to make some changes. It was impossible to
`turn the course into a two-semester sequence because we did not have any room in the
`curriculum. Thus, the only option we had was to reduce the course material, which was not an
`easy task. After all, the changes required eliminating some of the specializations thus postponing
`students’ first exposure to this material. Fortunately, because concepts related to logic design and
`computer architecture were already introduced in two other ECE courses, we were able to
`remove two chapters from the book and two experiments from the lab without experiencing a
`significant loss. Without the introductory material on digital signals, it was no longer possible to
`effectively discuss examples on computer networking; hence, it too had to be dropped. Also, we
`had always found it difficult to connect the material on networking to the introductory material
`covered during the first part of the course. Finally, the material on solid state electronics was
`also removed due to the lack of an organic link with the rest of the material.
`
`We have found by removing approximately one fourth of the course material it was possible to
`teach the rest effectively. Some of the older material was also replaced with new material to
`improve the continuity within the course and continuity with the future ECE core courses. These
`changes required major changes in the textbook in the form of either writing new chapters or
`major revisions. One of the most successful additions was a chapter on operational amplifiers,
`which came with an accompanying experiment.
`
`During this time, the lab manual and the experiments were continually revised based on the
`results of the student feedback surveys conducted after each experiment. The experiments,
`which were found too difficult were replaced with simpler experiments to help the students
`understand the concepts better. In the mean time, a virtual laboratory was created to allow the
`students experiment with virtual test instruments, which looked much like the equipment they
`used in the hardware laboratory. A semester-long mandatory hardware project was added to the
`laboratory, which also turned out to be a great success. Finally, an optional golden solder project
`was created for students interested in applying their new knowledge to a simple design project.
`
`When the dust settled after these changes, we were left with a new introductory course on
`signals, circuits and systems, which is the subject of this paper. The first part of the course covers
`fundamental concepts such as Kjrchoff’ s laws, Ohm’s law, AC and DC voltage sources, linear
`and non-linear resistive elements, capacitors, and representation of periodic signals in both time
`and frequency domains. As such, aside from the coverage on frequency domain, the first part
`closely resembles a traditional course on circuits. This however is not entirely true because the
`inclusion of frequency domain at this level represents a major deviation from the traditional
`
`

`

`approach, which truly affects the nature of the course contents. In every experiment, the response
`of a system (e.g. amplifier, filter etc.) is analyzed in both time and frequency domains.
`Consequently, the students completing the course attain an excellent understanding of how the
`two domains relate to each other before they begin to learn mathematical foundations of signals
`and systems in future core courses.
`
`Instructional objectives for the first part of the course are:
`
`8.
`
`1. Explain the concepts of electric charge, current, voltage, resistance, and capacitance.
`2.
`Identify resistors, diodes and capacitors in circuit diagrams.
`3
`Interpret the basic current-voltage (I-V) characteristics of key circuit elements, including
`resistors, photocells, diodes, and capacitors.
`4. Calculate the equivalent resistance of resistor circuits (i.e. series and parallel), and the
`equivalent capacitance of capacitive circuits (i.e. series and parallel).
`5. Apply Ohrn's Law and Kirchoffs Laws to simple circuits consisting of DC voltage
`sources, linear and non-linear resistive elements and capacitors.
`6. Given a first order RC Circuit, calculate the time constant and the time required to
`charge/discharge the capacitor to a certain voltage level.
`7. Given a first order RC Circuit, calculate the current flowing in the circuit at a given
`instant of time during charging or discharging.
`Identify/Measure/Calculate time-varying waveform parameters including amplitude,
`peak-to-peak value, frequency, period, duty cycle, average (DC) value, root-mean-square,
`phase angle and time delay, from graphs, oscilloscope screenshots, and equations.
`9. Apply Dhm‘s Law and Kirchoffs Laws to simple circuits consisting of AC at DC voltage
`sources, linear and non-linear resistive elements.
`10. Apply Ohm's Law and Kirchoffs Laws to fully analize half and full-wave rectifier
`circuits consisting of resistors and diodes to find the key voltage and current waveforms
`in the circuit given an arbitrary periodic input signal
`11. Determine and plot the instantaneous power dissipated on a resistive load given an
`arbitrary voltage waveform applied to the load in graphical or equation form, and use the
`instantaneous power to determine the real power.
`12. Determine and plot the instantaneous power dissipated on a non-resistive load given the
`sinusoidal voltage waveform and the resulting sinusoidal current including the phase
`angle between the two waveforms, use the voltage and current waveforms to determine
`the real and apparent power and power factor.
`13. Generate and analyze amplitude, phase and power spectra of periodic signals.
`14. Given amplitude or power spectrum of a periodic signal identify the waveform
`parameters including frequencies of the harmonics, average (DC) value, signal amplitude
`and power of each harmonic and total signal power.
`
`During the second half of the course, the fundamental concepts are applied to different examples
`of analog signal processing, which serve as exciting, real-life demonstrations of the material
`covered in the course. Applications include filtering, amplification, RF
`modulation/demodulation, sampling and reconstruction, which provide the natural platform to
`talk about different specialization areas. Fundamental concepts used under each application are
`shown in Figure 1 with links to other applications.
`
`

`

`Sampling 8.
`Reconstruction
`
`Multipiication
`so. wave 8. signal
`
`.
`Fmanng
`
`AM
`
` Analog Filters
`Amplifiers
`
`
`Modulation
`
`Multiplication
`
`
`
`sinusoid 84 signal
`
`
`Transfer
`Characteristic
`Clipping
`Distortion
`
`Distortion
`
`RF °°”°el°“
`
`Addition 8.
`Subtraction
`
`Signal Shaping
`
`
`Figure 1: Analog signal processing applications covered in the second half of the course and the
`"fundamental concepts covered under each application.
`
`TEXTBOOK AND LABORATORY EXPERIMENTS
`
`In this section, we provide brief descriptions of the material covered in different chapters and
`provide examples from experiments included in the the hardware laboratory.
`
`Part I: Introduction to Signals and Circuits
`
`Chapter}: Resistive Circuits:
`In this chapter, the students are introduced to Ohrn’s law and Kirchoff’ s laws. These laws are
`applied to analysis of simple circuits, which include DC voltage sources and resistive elements.
`Lectures emphasize the physical principles instead of techniques used to apply complex circuits.
`Concepts such as mesh and nodal analysis are left out to be covered in a follow-up course, which
`provides a more rigorous approach to circuit analysis. The guiding principle is to exclude
`abstract concepts, which can not be readily demonstrated to beginning students in the hardware
`laboratory. For instance, current sources are not mentioned because it is easy to talk about
`voltage sources by referring to batteries the students are already familiar with.
`
`The chapter includes both linear and non-linear resistive elements. Specifically, rectifying diodes
`and light emitting diodes are discussed and used in circuits with DC voltage sources. Inclusion
`of those non-linear elements provides opportunities for exciting experiments in the laboratory.
`
`The experiment for this chapter relies on the dedicated hardware box shown in Figure 2. The box
`allows construction of simple circuits with two independent loops sufficient to demonstrate basic
`concepts. The components are installed on small printed circuit boards with banana connectors.
`Switches on the board allow easy shunting of the circuit elements. This approach is preferred as
`opposed to using breadboards in order to allow the students to concentrate on their circuits
`
`
`
`Operational
`Amplifiers
`
`——u- Voltage Gain
`
`I- Voltage Gain
`
`i-
`
`PowerGain
`
`in
`
`Power Gain
`
`
`
`Voltage Gain
`
`PowerGain
`
`Frequency
`Response
`
`__
`
` i
`
`"'
`
`Frequency
`Response
`Transfer
`Characteristic
`
`Clipping
`
`
`
`

`

`instead of troubleshooting their connections on the breadboard. We have found this approach to
`be extremely helpful for beginning students who have no experience in using the breadboards.
`
`Figure 2: Experiment box used to construct and test circuits with two~termina1 elements.
`
`The first half of the experiment for this cha_pter demonstrates the following concepts, which are
`standard in all introductory experiments on circuits.
`
`How to use the multimeter to measure DC voltages and cunents.
`Resistor color coding
`Resistors in series and parallel
`Ohm’s law and Kirchoff‘ s laws
`
`Voltage and current division
`
`In the second half of the experiment, the students combine the above concepts with their
`knowledge of rectifying diodes to construct and test a night-light circuit, which turns on an LED
`when the ambient light is not sufficient. The circuit diagram is shown in Figure 3. The circuit
`works on the principle that when the ambient light is not sufficient, the photocell has a large
`resistance, hence, sufficient current can flow through the LED to turn it on. This is a practical
`circuit, which performs a familiar function, which the students are already familiar with.
`
`

`

`Vac
`
`LED
`
`photocell
`
`Figure 3: Night light circuit demonstrating Kircl1off‘s voltage and current laws.
`
`Chapter 2: Capacitors and RC Circuits:
`In this chapter, physical principles of charge storage in a capacitor are explained. This
`knowledge is then applied to analysis of first order RC circuits. Equations for capacitor charging
`and discharging are derived using the circuit laws introduced in the previous chapter. The
`solution to the differential equation is given and verified without teaching the techniques used to
`solve differential equations. Similar to the first chapter, the primary objective of this chapter is
`to emphasize the fundamental concepts such as understanding of the RC time constant as
`opposed to analysis of complex RC circuits, which are covered in the next course on circuits.
`
`In the laboratory, the students use the same experiment box used in the previous experiment.
`The experiment begins with measurements performed on a simple, first order RC circuit. Charge
`sharing in series and parallel capacitor connections is demonstrated. The final experiment for this
`chapter combines the new information on capacitors with their prior knowledge on LEDs in the
`timer circuit shown in Figure 4. In this circuit, LED remains off until the capacitor reaches the
`turn-on voltage of the LED. By using large electrolytic capacitors, the capacitor charging time
`can be increased to tens of seconds. Students use different capacitors and measure the time
`needed to turn on the LED. From these measurements and using the capacitor charging equation
`the students calculate the RC time constant of the circuit for different capacitors. Similar to the
`first experiment, this circuit applies the new knowledge to an exciting practical circuit, which the
`students can easily relate to.
`
`Voc
`
`LED
`
`Figure 4: Analog timer circuit used to demonstrate capacitor charging and Kirchoffs laws.
`
`Chapter 3: Periodic Signals in Time Domain
`The objective of this chapter is to introduce basic properties of common AC signals including the
`square and sinusoidal waveforms. Concepts of period, frequency, dutywcycle, phase, amplitude,
`peak-to-peak value and DC value are introduced with examples from standard test signals as well
`as signals generated by musical instruments.
`
`

`

`In the laboratory, the students are introduced to the fimction generator and the oscilloscope. The
`oscilloscope is networked, which allows the students to save their oscilloscope screenshots on
`their computers. The experiment begins with basic measurements on signals from the function
`generator. The laboratory hardware also includes a microphone allowing the students to observe
`different sound signals such as speech and sounds from different musical instruments on the
`oscilloscope. The students are encouraged to bring their own musical instruments to the lab for
`measurements.
`In addition, the course web-site provides recorded sounds of different
`instruments including classical guitar, ilute and drum.
`
`The experiment box used for the two first experiments is again used to construct a half-wave
`rectifier circuit, which applies their prior knowledge on diodes to a simple circuit including a
`sinusoidal voltage source. This is a key experiment, which provides an introduction to the
`mandatory semester long hardware project, which involves construction of a power supply. This
`project will be described later in this paper.
`
`Chapter 4: Electric Power
`In this chapter, students are introduced to the concept of electric power for both AC and DC
`signals.
`In addition to introducing electric power as a specialization area, this chapter provides
`fundamentals that will be used in analysis of periodic signals in frequency domain. The origin of
`the root-mean-square voltage of a periodic waveform is introduced as the DC equivalent voltage,
`which results in the same power consumption. The chapter begins with multiplication of voltage
`and current waveforms in time domain to find the instantaneous power dissipated on resistive
`elements. The students’ prior knowledge on average (DC) value of periodic signals is applied to
`‘ finding the average value of instantaneous power defined as real power. The coverage on non-
`resistive loads is limited to sinusoidal waveforms with a phase angle between voltage and current
`waveforms. The chapter provides a brief introduction to concepts of power factor and apparent
`power. The derivations are made entirely based on students’ prior knowledge of trigonometric
`identities.
`
`In the laboratory, experiments are carried out using a dedicated experiment box shown in Figure
`5, which houses a commercial light dimmer. A switch allows the user to bypass the dimmer if
`desired. A few inches of the wire carrying the load current is left outside the box, which allows
`the user to clamp a current probe over the wire. This way, the load voltage and current
`waveforms can both be displayed on the oscilloscope screen and then graphically multiplied to
`display the instantaneous power, using a standard feature on all modern oscilloscopes. Digital
`oscilloscopcs can also compute the average value of the displayed signal, which in this case is
`the real power. The input voltage to the box is 120 ‘W 60 Hz supply voltage. Standard electric
`outlets are used to measure the input and output voltage waveforms. A specially made, 100:1
`oscilloscope probe featuring a heavy—duty standard electrical plug is used to ensure safety during
`measurements. The experiment makes use of a desk lamp and an electric fan as examples of
`resistive and non—resistive loads. In the second part of the experiment, the light dimmer is used
`with the desk lamp. The students display the instantaneous power, evaluate the real power and
`correlate these numbers to the observed light intensity.
`
`

`

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`Power experiments.
`
`Chapter 5: Periodic Signals in Frequency Domain
`In this chapter, we introduce fundamental concepts used to analyze signals in frequency domain.
`Signal power at a given frequency is defined as the real power dissipated on a load resistance of
`I ohm building on the information provided to the students in the previous chapter. Students
`learn how to plot the amplitude, power and phase spectra of periodic signals. The decibel
`concept is introduced along with dBW as a unit of power. In this chapter, one of the key
`concepts is that every periodic signal can be represented as an infinite sum of sinusoids. We refer
`to Fourier series as the mathematical representation of a periodic signal but leave the derivation
`to future courses. During the lecture, students are shown how a square wave can be created by
`adding sinusoidal waveforms. Examples are given from nearly periodic signals generated by
`different musical instruments. The concept of noise is introduced along with definition of signal
`to noise ratio of a system.
`
`Representation of periodic signals in frequency domain is supported by actual measurements in
`the laboratory where students display the power spectra of various signals from the function
`generator, microphone or recorded music. Instead of dedicated spectrum analyzers, oscilloseopes
`with Fast-Fourier-Transform (FFT) capability are used to display the power spectra.
`
`

`

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`Figure 6: Experiment box used for experiments on two-port circuits.
`
`Part 11: Introduction to Analog Signal Processing and Systems
`
`Chapter 6: Filters
`This chapter covers basics of analog filtering. The frequency response of a two-port circuit is
`discussed along with discussion on the voltage and power gain of a filter. Ideal low-pass, band-
`pass and high-pass filter are introduced. Examples of non-ideal filters are provided and the
`concept of 3-dB cut-off frequency is introduced. Students learn how to find the outpu.t power
`spectrum given the power spectrum of the input signal and the arbitrary frequency response of
`the filter using the the fundamental knowledge provided in the previous chapter.
`
`In the laboratory, the experiment box shown in Figure 5 is used. This box provides card edge
`connectors for two-port circuits on PC boards to create a multi-stage system. The input signal to
`the box can be supplied from a function generator or an audio source. The output can be
`connected to headphones or to an audio speaker. The user can display the signal at various points
`on the circuit via BNC connectors provided.
`
`In this experiment, an 8”’ order lowwpass filter with a variable cut-off frequency is used to
`demonstrate the filtering action. An amplifier is used as a second stage allowing the output
`signal to be applied to an audio speaker. First, filtering of a square wave is demonstrated. By
`observing the output signal in both time and frequency domains the students can see how the
`output signal transforms from a square wave with sharp corners to a pure sinusoid as the
`harmonics are eliminated one by one. The 8"‘ order filter is sharp enough to create a beautiful
`demonstration of this phenomenon. The filter is then tested with audio signals again observing
`the signals in both domains. Audio files available on the course web site are used as examples of
`
`

`

`signals generated by different musical instruments. Students as usual are encouraged to bring
`their own musical instruments.
`
`Chapter 7: Arnpléficatian
`This chapter builds on the concepts introduced for filters in the previous chapter. The tact that an
`amplifier needs an external voltage source to operate is emphasized as a property of real
`electronic systems. Students learn how to sketch the transfer characteristic of an amplifier given
`its voltage gain and the power supply voltage. Output clipping is discussed as a form of
`harmonic distortion. Students use the transfer characteristic of an amplifier to detennine the
`largest input signal that can be amplified without clipping.
`
`In the laboratory, the twtvport circuits box shown in Figure 6 is used with ditilierent amplifier
`circuits (Figure 7) inserted in the card edge connectors. The experiment includes measurements
`of the voltage gain, clipping and observing the clipping distortion in both time and frequency
`domains. The students learn how to compute the total harmonic distortion of an amplifier given
`the power spectrum resulting from a clipped sinusoidal test waveform. During the experiment,
`the. students observe the waveforms in both time and frequency domains while they listen to the
`changes in the sound output.
`
`
`
`/__:_
`
`Figure 7: An amplifier with a variable voltage gain.
`
`These experiments are designed to reinforce th.c power spectrum and Fourier series concepts.
`For instance, it is emphasized that a clipped sinusoid is a periodic signal, hence, it should have
`harmonies appearing at multiples ofthe fundamental frequency.
`
`Chapter 8: Operational Armpit’/iers
`This chapter introduces the students to versatile operational amplifiers, which can be used to
`realize the filters and amplifiers discussed in the previous two chapters. Students learn how to
`
`

`

`analyze operational amplifier circuits following standard procedures including the virtual short
`concept. Examples mostly cover circuits with resistive elements. A few examples of circuits
`involving capacitors and nonvresistive elements (e.g. integrators and differentiators) are also
`given as examples of signal shaping circuits.
`
`In the laboratory, operational amplifiers are used to amplify signals in two practical applications.
`In the first experiment, students amplify the signals from an ultrasonic emitter/receive pair. The
`objective of the experiment is to measure the speed of sound by measuring the time delay
`between the original and reflected signals. In the second experiment, an operational amplifier is
`used to amplify the signal from an infrared eniitter/detector pair used to measure the speed of a
`variable speed DC motor. Both the motor and the emitter/detector pair are mounted on a PC
`board, which can be readily inserted into a card edge connector.
`
`
`
`Figure 8: Ultrasound emitter/detector pair.
`
`The applications mentioned above were both taken from a senior level robotics class. We
`believe that they lead to exciting experiments while demonstrating the versatility of operational
`amplifiers.
`
`Chapter 9: AM Modulation
`In this chapter, signal multiplication is introduced as a new signal processing technique and AM
`Modulation is discussed as an application of signal multiplication. Again, the AM signals are
`analyzed in both time and frequency domains. This opportunity is used to introduce a variety of
`general concepts on transmission and reception of radio frequency signals and talk about
`communication as a specialization area.
`
`In the laboratory, students create their own radio stations using the AM feature of their function
`generators. The Agilentm function generators used in our laboratory can generate a carrier
`sinusoid, while accepting the modulating signal from an outside voltage source (c.g. an audio
`source) providing a simple method to construct a transmitter. A loose banana cable is used as the
`
`

`

`antenna for the transmitters. The range of these transmitters is no more than a few feet allowing
`many radio stations to function in the same laboratory simultaneously. The transmitted signals
`are first received by commercial radio receivers and then by students’ very own crystal radios.
`The students’ prior knowledge of the half-wave rectifier is used to explain how the envelope
`detectors (crystal radio) demodulate the AM signals. Shown in Figure 9 is the experiment box
`used featuring the crystal radio and an amplifier allowing the output signal to be applied to an
`audio speaker.
`
`Figure 9: AM Radio box.
`
`Chapter I0: San-zpling and Reconstruction
`This chapter builds on the concepts introduced in the previous chapter. We use a simple method
`to teach sampling based on signal multiplication and trigonometry. In tl1e lectures, it is stated
`that the sampling is equivalent to multiplying an arbitrary signal with a square pulse train with
`narrow pulse widths. Since the sampling signal can be represented as an infinite sum of
`sinusoids at multiples of the sampling frequency, we can View the sampling process as
`multiplying the original signal with each harmonic of the square wave one by one. Since each
`multiplication results in sum and difference frequencies, the original spectrum and its mirror
`image is repeated at multiples of the sampling frequency. Since the original square wave also
`has a non-zero average value, it produces a smaller replica of the original spectrum without
`
`

`

`changing the frequencies of the original harmonics. Reconstruction is achieved by low-pass
`filtering to eliminate all the higher frequency doubles except the replica of the original spectrum.
`
`This chapter provides ample opportunity to discuss various specialization areas including digital
`communications, digital signal processing and electronic circuits. The chapter also provides an
`exciting medium for applying a large variety of concepts introduced in the course to practical
`systems such as CD players.
`
`In the laboratory, a dedicated experiment box is used, which accepts different components of the
`sampling and reconstruction system on PC boards. These include two low-pass filters with
`variable cut-off frequencies, analog switch for sampling, a 555 timer circuit generating the clock
`signal to derive the analog switch and an amplifier. The students can change the sampling rate as
`well as the cut-off frequency of the low-pass reconstruction filter and listen to the effects of these
`changes on the produced sound.
`
`VIRTUAL LABORATORY
`
`The virtual laboratory was created to support the experience gained in the hardware laboratory.
`Our ass