Homework answers / question archive / M21388 Introduction to Analogue Circuits Coursework2 Overview of the Coursework 2 for Teaching Block 2 Coursework 2 described in this document is divided into two sections

M21388 Introduction to Analogue Circuits Coursework2 Overview of the Coursework 2 for Teaching Block 2 Coursework 2 described in this document is divided into two sections

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M21388 Introduction to Analogue Circuits
Coursework2

Overview of the Coursework 2 for Teaching Block 2
Coursework 2 described in this document is divided into two sections. The first section (Section 1 - Investigation of operational amplifier circuits) has four simulation experiments involving operational amplifiers, designed to reinforce the theory covered during the lectures. The second section (Section 2 - Project to design an MP3 headphone amplifier) is a project in which you will be required to design a circuit to meet a given specification and requirements.
Assessment
Section 1 (Investigation of operational amplifier circuits)
Section 1 is assessed on a pass/fail basis in which marks are deducted from that obtained in the main project (Section 2 described below) for failure to complete the four simulation experiments. 10% will be deducted from the main project mark for each experiment that has not been achieved.
Section 2 (Project to design an MP3 headphone amplifier)
Details of the assessment and marking scheme are presented below. The mark you attain in your project is subject to a penalty of up to 40% if you fail to complete the Section 1 activities (as stated above).
Examples of how the assessment rules are applied
Peter completed all experiments of Section 1 satisfactorily. He then obtained 60% in the Section 2 project. Because he had no penalties applied from Section 1, he retained the 60% from Section 2, so 60 marks were awarded.
Susan did not satisfactorily complete two of the four experiments in Section 1. Consequently, a penalty of 20% in Section 2 was applied. The mark for Section 2 was 56%. Her 56% project mark was reduced by 20% (subtractive penalty) to 36%, so 36 marks were awarded.
A report covering all work including circuit design, theoretical calculation (prediction), simulation analysis and evaluation should be submitted before the deadline. All source files (.asc files) ready for simulation should be submitted together with the report. The marks and the feedback on the report will be given within 20 working days after submission. Please be warned that the plagiarism detection software will be used on your submission.
Working practices
You should work individually and complete the coursework independently. Although the Multisim simulation software can be used for the coursework, the LTspice simulator is strongly recommended because this simulator is free and is therefore not restricted by license issues. LTspice has been selected as the main tool to be used throughout the module, and it will be used in other modules too.
You are encouraged to seek advice and obtain feedback on what you have already done at any, and preferably on several occasions.
Section 1 – Investigation of Operational Amplifier Circuits
Experiment 1: Inverting Amplifier
The purpose of this experiment is to build and investigate one of the two most common operational amplifier circuits. You should be able to reconcile and reinforce what you are learning in lectures.
The pin configuration of the operational amplifier is shown in Fig. 1 and its pin functions are shown in Table 1.
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Fig. 1 Pin configuration of LM741 (courtesy of the Texas Instruments)
Table 1 Pin Functions of LM741 (courtesy of the Texas Instruments)
The circuit diagram of an inverting amplifier circuit is shown in Fig. 2 below. The input signal (generated by a function generator) is a 1 kHz sine wave with an amplitude of 0.5 V. The positive supply voltage of the operational amplifier is 15 V and the negative supply voltage is -15 V.
Please note that circuit diagrams for op-amp circuits generally don’t show power supply connections but these should be included in simulation (as well as in real circuits) to ensure the circuits operate normally.
Fig. 2 An inverting amplifier.
Tasks for Experiment 1:
• Build up the circuit in the LTSpice simulator.
• Complete the simulation analysis and capture the waveforms of the input signal and the output signal of the circuits.
• Compare the input and the output signals and explain the results.
• What is the measured and theoretical value of gain (show calculations)?
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• Investigate what happens at high frequencies (gradually increase the frequency and look for attenuation and distortion). Describe the manner in which attenuation changes with frequency. Describe the distortion you observe at high frequencies. Capture a waveform to illustrate this.
• Keeping the amplitude of the input constant, measure the amplitude of the output at the following frequencies: 10Hz, 100Hz, 1kHz, 5kHz, 10kHz, 20kHz, 30kHz, 40kHz, 50kHz. Tabulate your results.
• What is the input impedance of this amplifier circuit? What are the implications of this result?
Evidence required in your report for the assessment of Experiment 1
• Title of your investigation.
• Description of your investigation (what did you do).
• Circuit diagram.
• Captured waveforms labelled with all relevant parameters.
• Discussion of results. This must fully explain your findings.
• Full source files ready for simulation (submitted along with the report).
Experiment 2: Non-inverting Amplifier
The purpose of this experiment is to build and investigate the other one of the two most common operational amplifier circuits. You should be able to reconcile and reinforce what you are learning in lectures.
The circuit diagram of the non-inverting amplifier is shown in Fig. 3. The positive supply voltage of the operational amplifier is 15 V and the negative supply voltage is -15 V.
Fig.3 A non-inverting amplifier.
Tasks for Experiment 2:
• If R1 has a resistance value of 1 kΩ and the voltage gain of the circuit is 11, please determine the theoretical value of R2 (show calculations).
• Please build up the circuit in the LTSpice simulator and verify your design.
• Capture the waveforms of the input signal and the output signal of the circuits.
• What is the input impedance of this amplifier circuit? What are the implications of this result?
Evidence required in your report for the assessment of Experiment 2
• Title of your investigation.
• Description of your investigation (what did you do).
• Circuit diagram.
• Captured waveforms labelled with all relevant parameters.
• Discussion of results. This must fully explain your findings.
• Full source files ready for simulation (submitted along with the report).
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Experiment 3: Current source
Current sources are often used in electronic circuits to provide a constant bias current to transistors. They are also used in battery chargers and in led lighting circuits where the brightness is related to current and this is the preferred control variable.
The circuit in Fig. 4 is a current source for a floating load (in this case the 10 kΩ variable resistor). Floating in this context means not connected to ground. The positive supply voltage of the operational amplifier is 15 V and the negative supply voltage is -15 V.
Fig. 4 A current source circuit.
Tasks for Experiment 3:
• Calculate the voltage and the current through the 180 Ω resistor.
• If the load resistor has a value of 2 kΩ, calculate the voltage and the current of the output of the operational amplifier.
• Explain why the current flowing through the load resistor has a constant value.
• Build up the circuit in the LTSpice simulator, verify your calculation and capture the waveform of the current.
• Vary the load resistor value between 0 and 4 kΩ and choose 10 sensibly values to measure the current flowing through the load resistor. Please record and tabulate your results and explain why the value of the current cannot keep constant when the load resistance is not appropriately chosen.
Evidence required in your report for the assessment of Experiment 3
• Title of your investigation.
• Description of your investigation (what did you do).
• Circuit diagram.
• Captured waveforms labelled with all relevant parameters.
• Discussion of results. This must fully explain your findings.
• Full source files ready for simulation (submitted along with the report).
Experiment 4: Summing Amplifier
The summing amplifier is another example of an important practical circuit. There are many applications of this type of circuit, for example, audio mixer, digital to analogue converter or LED modulation circuit.
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The circuit you will be investigating, shown in Fig. 5, is designed to simply add an offset to an input signal. An example of where this might be required is if you had an analogue to digital converter IC which required the input signal to range between two voltages that didn’t match the voltage range of the existing input. Typically, the signal to be converted would be symmetrical about zero volts. It is common for an analogue to digital converter to require the input to range either between 0 and some positive value, or between two positive voltages (for instance, 1 – 4 V). In this example, the middle of the existing range is zero and the middle of the required range is 2.5 V.
The circuit in Fig. 5 is a summing amplifier. The positive supply voltage of the operational amplifier is 15 V and the negative supply voltage is -15 V.
Fig. 5 A summing amplifier.
Tasks for Experiment 4:
• Assuming the output of the potentiometer is VR, please derive an expression for VOUT in terms of VIN and VR.
• If VIN is a 1 kHz sine wave signal with an amplitude of 2 V and a zero DC offset, please determine VR so that the output signal VOUT has a DC offset of 2 V.
• Build up the circuit in the LTSpice simulator verify your calculation and capture the waveforms of the input and the output signals.
Evidence required in your report for the assessment of Experiment 4
• Title of your investigation.
• Description of your investigation (what did you do).
• Circuit diagram.
• Captured waveforms labelled with all relevant parameters.
• Discussion of results. This must fully explain your findings.
• Full source files ready for simulation (submitted along with the report).
Section 2 – Project to Design an MP3 Headphone Amplifier
2.1 Introduction
The aim of this project is to design a stereo headphone amplifier to be used with an MP3 player such as an iPod or mobile phone with music playing capabilities.
The input signal of a headphone is typically an AC signal with a maximum voltage amplitude of 2 V and with no DC offset. The root mean square (RMS) value of the AC signal is around 1.414 V. The input impedance of headphones typically varies between several tens Ohms and up to several hundred Ohms. Assuming the input impedance is 32 Ω, the maximum power consumed by the headphone will be 62.5 mW.
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The maximum amplitude of the output voltage of a mobile phone is normally less than 1 V and the output impedance of the mobile phone is approximately several Ohms. To increase the sound quality output by the headphone, an amplifier can be introduced between the mobile phone and the headphone, which is shown in Fig. 6.
Assuming the amplitude of the output voltage of a mobile phone is 0.2 V and the output impedance is around 10 Ω, and assuming the input impedance of the headphone is 32 Ω and the maximum power consumption is 62.5 mW, you are expected to design the amplifier and verify it using the LTSpice simulator.
Fig. 6 An MP3 headphone amplifier
2.2 Specification and requirements for the amplifier
• Have a maximum output voltage amplitude of 2 V across the headphone.
• Have a frequency response of at least 20 Hz – 20 kHz (this means that the lower limit should be <20Hz and the upper limit >20 kHz).
• Have a volume control (the amplitude of the voltage across the headphone can be changed between 0 and 2 V).
• Don’t have DC signals in the outputs (consider using a capacitor in the output stage).
• Operate from a 15 V DC supply.
• You may use transistors or operational amplifiers in your design.
2.3 Assessment
You should work individually and submit your report together with your full source files. The design, the simulation and the evaluation of the circuit should be shown in the report. Your source files must be ready for simulation so please test them before submission. Feedback will be given within 20 working days after submission.
2.4 Marking Scheme
Introduction– 10 marks
Write an introduction to the project aimed at a non-technical audience. This should briefly set out the background, the motivation, the aims and the objectives of the project. Note that the emphasis is on writing in a style that a lay person would be able to understand.
Literature review - 10 marks
Before designing your circuit, carry out a literature review to find out about similar products. Try to discover:
• why people use them;
• what are the advantages of using a headphone amplifier;
• what are the design trade-offs;
• what commercial products are available;
• what are the key specifications for these products in terms of parameter types such as noise, output power, distortion and anything else you can identify.
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Identify a number of designs that you think are contenders for your project and evaluate them to determine the one you think is the most suitable. The total amount of words should not exceed 1500. Please include a reference section at the back of the report to indicate your sources (this does not contribute to the word limit). Please use the Harvard APA referencing system.
Description and analysis of your chosen circuit - 15 marks
When you have carried out the literature review and identified a suitable design, write in your report a clear and detailed explanation of how the circuit works in your own words. Any analysis that is needed to justify any aspect of the design should also be included.
Evaluation of your circuit – 20 marks
Design the circuit and test it through simulation to see if it meets the specification. You may measure the output voltage, the frequency response, and any other parameter your research has led you to believe may be relevant. Write up your evaluation in your report along with a conclusion and suggestions for future work.
Lecturer assessment of the circuit – 25 marks
• Whether the voltage amplitude across the headphone has a maximum value of 2 V (5 marks).
• Whether the voltage amplitude across the headphone is controllable (please specify how the voltage can be adjusted from 0 to 2 V in your report) (10 marks).
• Whether has a frequency response of 20 Hz to 20 kHz (5 marks).
• Whether has a DC signal in the output (5 marks).
Summary – 10 marks
Write a summary of the project aimed at a non-technical audience. You should summarise the work you have done for this project design. You can also include conclusions and future work for this research. Note that the emphasis is on writing in a style that a lay person would be able to understand.
Quality of report writing and formatting/presentation – 10 marks
This includes the standard of the English grammar and punctuation, the quality of diagrams and the degree to which the report is well structured, enabling a reader to understand what you have done and why.