# Electrical and Electronic Engineering CIRCUIT ANALYSIS Module Code : 5EJ501 Level 5

## Description:

You are required to submit an assignment of two-parts part A and B of a maximum of 2,500 words.
Directed studies work introduced in the lecture, laboratory & tutorial sessions will form the basis for most of the assignment topics, but you are encouraged to extend the assignment according to your own interests and professional skills development needs and to use the assignment as a platform for becoming more proactive with circuit design, analysis and development activities and wider personal development opportunities.

The assignment must include and explore the following prescribed four topics:

1. R-L-C Circuits Rise/Fall Time Measurement:
When making this measurement, you are only concerned with time. The measurement is made on a single signal, using square wave excitation. Identify the 10% and 90% indications on the ‘scope screen (usually accompanied by dotted lines). Adjust the displayed signal amplitude so that the steady state values of the measure and signal lie on the lines just outside the 10% and 90%
lines. It is then occupying “100%”. Measure the time taken for the signal to move from the 10% value to the 90% value (or 90% to10%, if fall time).
2. R-L-C Circuits Phase Measurement:
When making this measurement, you are making neither a time measurement, nor a voltage measurement. We are just comparing the relative position of the two waveforms. Therefore,
both vertical and horizontal scales can be put out of calibration, to ease the measurement. The measurement is made with two sinusoidal signals. Adjust the two traces so that they are
symmetrical about the central horizontal line on the display, preferably so that the display amplitudes are equal, and so that one cycle occupies exactly 8 cm horizontal of the trace. Now each
division is worth (360/8), i.e., 45o , or each subdivision worth (45/5), i.e., 9o. Carefully measure the distance in zero-crossing, expressed in degrees, between the two traces, noting which is
3. R-L-C Circuits Rate of Change and Resonance Frequency Measurement:
When making this measurement, we are making both a time and Circuit Analysis Module Assignment
frequency measurement, and a voltage measurement. Both vertical and horizontal scales should therefore be in calibration. For constant rate of change (i.e., trace is a straight line), adjust
the trace so that it fills a substantial portion of the screen. For a convenient portion of it (usually between points where it crosses the display grid), measure the change in voltage, and the related
change in time. Deduce the voltage rate of change in Volts per second, or Volts per microsecond. For a changing rate of change (i.e., trace is curved), a similar procedure should be adopted, but
the point at which the rate of change is desired should be clearly identified. This should be placed on the central horizontal grid line, and an imaginary tangent drawn. The rate of change of the
tangent should be deduced.
4. Non-linear circuits design and analysis using computer simulation software:
Computer aided design tools are one of the essential process in products development lifecycle and one the critical skills that engineers must have. As part of this report, you are required to include four case studies of part B that showing your ability to obtain a solution of non-linear circuits using computer aided design and simulation software – NI-MULTISIM.
Full details will be provided in learning and teaching sessions and published via Course resources.
In fundamental nature the assignment is designed to support your development as an undergraduate learner and to outline a process of personal verification and evaluation. The purpose of learning is to develop competent graduates that are creative, with new ideas, new capabilities and skills. Use this assignment as a first step in redefining yourself as a professional.

## PART_A

### R-L-C Circuits Rise Time, Phase Angle and Voltage Rate of Change Measurements

Introduction:

In simple applications of the oscilloscope, measurements are taken of time and voltage.
Vertical and Horizontal scales are in calibrated position. The measurements in this practical
require more advanced interpretation of the information presented on the oscilloscope
screen and may also require the scales to be put out of calibration. You need to carry out
the following tasks and report them in detail.
Equipment:

LJ D3000 kit, AC Circuits card, signal generator, oscilloscope …etc.

1. Rise/Fall Time Measurement:
Rise or fall time measurements are of interest when there is an instantaneous “step change”
in applied voltage. While we often associate this with a switch opening or closing, it is difficult
to measure a single event like this on an oscilloscope (at least without a storage ‘scope).
Therefore, with these tests we use a repetitive event, i.e. a square wave, to explore circuit
response to an instantaneous change of voltage.
1.1 L-R Circuits – Current Rise/Fall Time:
Connect up the circuit of Figure 1a). Select R to be 4k7, and set L in turn to 68mH, 100mH,
and 200mH. For each combination:
▪ Calculate the expected current rise time,
▪ Measure the current rise time,
▪ Measure the steady state current,
▪ Record the applied voltage amplitude.

Draw a simple sketch showing how the measurement was made and or take a screen shoot of actual practical arrangement. Ensure you are making full use of the facilities of the ‘scope and signal generator as you do this. Record the settings you use. Is the measured fall time equal to the rise time? Explain the use of the 10-ohm resistor. Why is it labelled current monitor and under what circumstances is it permissible to use this measurement technique?

1.2 R-C Circuits – Capacitor Voltage Rise/Fall Time:
Connect up the circuit of Figure 1b). Set R to 10k, and set C in turn to 470pF, 1n, and 2nF. In each case calculate the expected voltage rise time, and then measure it. Also use the combination R = 100k, C = 2nF. Measure also and record the steady state applied voltage, and capacitor voltage. Ensure you are making full use of the facilities of the ‘scope and signal generator as you do this. Record the settings you use. Is the measured fall time equal to the rise time?

Phase Measurement:
2.1 L-R Circuits:
Set up the circuit of Figure 1a) again, but now apply a sine wave. For combinations listed below, measure the phase angle between signal generator voltage, and circuit current. Please do record which one is leading. Measure also applied voltage and current (both peak to peak). Are you able to predict all these values theoretically?
f = 11 kHz, R = 4k7, L = 68mH
f = 11 kHz, R = 6k9, L = 100mH
2.2 R-C Circuits
Set up the circuit of Figure 1b) again but include a current monitor resistor. Apply a sine wave. For combinations listed below, measure the phase angle between signal generator voltage, and circuit current. Please do record which one is leading. Measure also applied voltage and current (both peak to peak). Are you able to predict these values theoretically?
f = 16 kHz, R = 10k, C = 1nF
f = 16 kHz, R = 10k, C = 2nF

Voltage Rate of Change and Resonant Frequency Measurements
3.1 Voltage Rate of Change
Connect the ‘scope directly to the signal generator output. For each of the signals below, measure the voltage rate of change:
Triangle wave, 15 kHz, 4Vp-p, rising and falling slopes,
Triangle wave, 15 kHz, 8Vp-p, rising and falling slopes,
Triangle wave, 10 kHz, 4Vp-p, rising and falling slopes,
Triangle wave, 10 kHz, 8Vp-p, rising and falling slopes,
Sine wave, 15 kHz, 4Vp-p, rising, at zero crossing,
Sine wave, 15 kHz, 8Vp-p, rising, at zero crossing,
Sine wave, 10 kHz, 4Vp-p, rising, at zero crossing,
Sine wave, 10 kHz, 8Vp-p, rising, at zero crossing
Are you able to predict these values theoretically?

3.2 Resonant Frequency Measurement
Connect the circuit shown in Figure 2, with L = 10mH, and C = 1nF. Adjust the signal
generator frequency so that the resonant oscillation is clearly displayed. Measure its
frequency. Are you able to predict its value theoretically? Change the signal generator output
to sinusoidal and find the frequency which gives the maximum capacitor voltage. At this
frequency, record both signal generator voltage, and capacitor voltage. What is the phase
angle between these two voltages?

## PART_B

### Computer Simulation and Modeling of Nonlinear Circuits Using CAD Software Tools and Verification using D3000 Op-Amp Development Kits

Introduction:
The development life cycle of an electrical and electronic circuits designs normally pass through a number of stages. This includes design, analysis, computer simulation and modelling, prototyping, testing, refining and validation. In this practical session students will exercise design and analysis, computer simulation using CAD tools, build and prototyping of a practical prototype circuit using available development kits.
Equipment:
PC with MUTLISIM CAD Tools, LJ D3000 development kits, Transistor Circuits card, OpAmp Circuits card, signal generator, oscilloscope, test rig platform and power supply source.

1.Network Theorem Design and Analysis Techniques:
1.1 Resistors Series, Parallel and Kirchhoff Current Law Analysis:
2 Design the circuit shown in Figure 3,
3 Obtain the circuit equations using Kirchhoff current law, there is no need to solve them.
4 Use the simulation analysis to explore Kirchhoff Analysis and circuit theory principles and

1.2 Thévenin’s Equivalent and Maximum Power Transfer:
▪ Design the circuit shown in Figure 4,
▪ Obtain the circuit equations using Kirchhoff current law, there is no need to solve them.
▪ Use parameters sweep analysis to see the voltage output over a range of load
resistance,
▪ Choose Simulate/Analysis/Parameters Sweep,
▪ Once the results displayed in the graph, choose Tools/Export to Excel to transfer the
analysis results to an Excel file,
▪ Load the sample Excel file, maxpower.xls, to view how you can process Multisim results
in Excel to further explore circuit theory and report your findings.

1.3 RLC Circuit Design and Analysis – Change in Output Due to Device Tolerance:
▪ Design the circuit shown in Figure 5,
▪ Choose Simulate/Run to view the simulation using Virtual Oscilloscope,
▪ Use Monte Carlo Analysis to see the effect of Statistical Variations in Resistance through R1,
▪ Monte Carlo Analysis is used here to illustrate possible change in the output due to

1.4 Bridge Rectifier Circuit and RC Filter Design and Analysis:
▪ Design the circuit shown in Figure 6,
▪ Sketch the expected waveform at the output of the bridge rectifier,
▪ Sketch the expected waveform at the output of the filter. Label each significant point,
▪ Run the simulation and compare your results.
To run the simulation:
▪ Select Run under the Simulate menu (or click on the ON switch),
To view the instrument front panels:
▪ Double click on the instrument icons on the workspace

Design and Build of Transistor Circuit for Industrial Applications
2.1 Class A Power Amplifier:

The circuit Figure 7 illustrates Class A common- emitter power amplifier and is recommended for
conducting an analysis of the amplifier.
[For maximum output signal, the Q-point must be centered where a non-centered Q-point limits the
output swing]
Experiments:
▪ Verify the parameters being measured by the various Multimeter. (What are they? What are their
clues/evidences/explanation?)
▪ Calculate the maximum AC output current and DC input power using the formulas given by:
V ceq= max collector-to-emitter voltage swing, I cq= max collector current swing.
▪ Calculate the efficiency and discuss the result from a Class A amplifier.

2.2 Class B Push-Pull Power Amplifier:
The circuit Figure 8 illustrates Class B Push-Pull emitter-follower amplifier and may be used
to demonstrate its design and operation. The circuit consists of a pair of complementary
transistors (NPN and PNP), each of which is biased at the cut-off point. The input is
sufficient to forward-bias each transistor on the appropriate half cycle of the input waveform.
As a result, crossover distortion occurs.
Experiments:
▪ Observe amplifier input and output waveforms.
▪ Have you noticed any changes to the output waveform? Is it distorted in the vicinity of 0
volts? Is there a phase shift between the input and output signals? (Hint: No.) Explain
why?
▪ Referring to the waveforms on the scope, find the base-to-emitter voltages required for
both transistors to eliminate crossover distortion.

2.3 Class AB Power Amplifier:
The circuit Figure 9 demonstrates the design and operation of a class AB amplifier. A class AB
amplifier is obtained from a class B push-pull amplifier that has the crossover distortion effect
eliminated. The crossover distortion effect is eliminated by biasing both transistors at a point slightly
above their cut-off point. By connecting two silicon diodes (D1 and D2) to the base terminals of the
transistors, the biasing voltage applied to the transistors is equal to the forward voltage drop of the
diode. These two diodes are generally called Biasing Diodes or Compensating Diodes and are
chosen to match the characteristics of the matching transistors.
Experiments:
Change the value of the input voltage and carefully observe the resulting output voltage waveform.
What are the findings?

Design and Build of a Signal Conditioning Unit using Op-Amp for Industrial Applications
3.1 A transducer for one of the industrial applications has internal impedance that is always less than 50 Ohms but is variable over time. A signal conditioning unit that produces an amplified version of the internal source voltages vs is required. The voltage gain should be−10 10 percent.
▪ Design a signal conditioning unit for this application,
▪ Use Multisim CAD software to simulate the unit,
▪ Connect the designed circuit using D3000 Op-Amp development kit and record the input and output signal.
▪ Report your findings and explain the design process of the unit?
3.2 The circuit shown in Figure 10 is an ADD Inverting operational amplifier:
▪ Obtain the mathematical expression of the Op-Amp output using basic circuit analysis
principles,
▪ Calculate the out voltage if V1, V2 and V3 are equal to 100, 200 and 300 milli volts,
respectively,
▪ Use Multisim CAD software to simulate the system, then compare between the results of
point b and c.
▪ Connect the circuit shown in Figure 8 using D3000 Op-Amp development kit and record
the input and output signal.

3.3 Design the Integrator Circuit shown in Figure 11, Apply an input square wave with
Frequency= 1 kHz and Amplitude = 10 V, calculate the expected output voltage then run
the simulation to compare results.
▪ Sketch the expected waveform at the output of the integrator, Use the simulation to
obtain the input and output waveform, use noise analysis to analyse the circuit and its
performance,
▪ Repeat the above design using tree feedback arrangement and then repeat the steps
above, report and explain your findings.

3.4 Analog Design and Analysis – Low Distortion Sine Wave Oscillator:
▪ Design the circuit shown in Figure 12,
▪ Sketch the expected waveform at the output of the integrator,
▪ Use the simulation to obtain the input and output waveform,
Note that the output will stabilize after approximately 5 sec

3.5 Analog Design and Analysis – Wien-Bridge Oscillator:
▪ Design the circuit shown in Figure 13,
▪ Sketch the expected waveform at the output of the integrator,
▪ Use the simulation to obtain the input and output waveform,

To see the oscillations, lower the value of the variable resistance by pressing Shift-A

3.6 Circuit Parameters Application – Active Bandpass filter:
The circuit in Figure 14 demonstrates the operation and characteristics of an active Bandpass filter. It allows all input signal frequencies within a given range (called bandwidth) to pass through, while rejecting those outside the range.
Experiments:
▪ Calculate the centre frequency (fo). Also verify the centre-frequency voltage gain using the formula:
Go =R3/2R1
▪ Use the function generator to vary the input frequency until the peak output voltage(V out) reaches its maximum. What is this single frequency called? What is its value?
▪ Referring to the waveforms on the scope, verify the centre-frequency voltage gain( Go =V out/V input) and compare the result with the previously calculated value. Is it about
1.2? Is the output signal in phase with the input? (Hint: No, it is not.)

▪ Determine the filter’s bandwidth. With the centre frequency set to about 750 Hz, the output voltage equal to 1.0V and the output frequency constant, do the following:
▪ Decrease the input frequency until the peak-to-peak Vout reaches 0.7 V; note the fin. Is it about 550 Hz?
▪ Increase the input frequency until the peak-to-peak Vout reaches 0.7 V; note the fin. Is it about 1 kHz? Now, you are ready to specify the filter’s bandwidth. What is it?

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