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Project Instructions Sheet
Design of Phase Shift Oscillator Using Op-Amp
Electronic Devices and Circuit Prototyping (EDCP)
International Year One in Engineering
International Study Centre (ISC)
University of Sussex
Contact: Dr Alaa Hussein XXXXXXXXXX
This software simulation-based project forms one of your assessed submissions and will be used to
assess your practical and theoretical progress in this module. It will also assess your technical report
writing skills. The report is weighted 25% of your total grade of this module.
2. Project Brief
This project exercise is based on the work you do to design and study the operation and
characteristics of phase shift oscillator based on op-amp using Multisim software tool.
3. Software Tool
You will need to use Multisim software tool to complete this project. This software can be installed
on your PC from this link https:
multisim or you can use Multisim Live on https:
4. Background of Phase Shift Oscillator
In general oscillation occurs in a circuit when there is positive feedback from the output to the input
(i.e. a phase shift of 0° or 360° between the output and the input), and simultaneously the overall
gain of the circuit is equal to or greater than one. For a circuit to oscillate at a single frequency, i.e.,
for a sine wave oscillator, this condition should occur at only one frequency.
A network consisting of a capacitor and a resistor in series has a phase that varies with frequency.
The largest phase shift that can be obtained with one capacitor and one resistor is less than 90°.
However, with three identical RC networks, one after the other, it is easy to obtain a 180° phase
shift at some particular frequency. We can then combine this with an inverting amplifier for a total
phase shift of 360°. The analysis is a little complicated because the three different RC networks load
each other. It turns out that the total attenuation of all three networks is a factor of 29, so that in
order to oscillate they must be combined with an amplifier that has at least that gain. The frequency
at which this occurs is given by:
Careful: Do not confuse this formula with the formula for a 45° phase shift RC network which does
not contain a factor of 6.
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a) Design an inverting op-amp circuit with a gain of about 60 as shown in Figure 1 below.
) Using ?0 equation, design a three stage RC filter network which has a gain of 1/29 and a
phase shift of 180° at a frequency near 1 ???. Note that ?2 should be greater than ?. Why?
Construct these and connect them as shown in Figure 1. What values did you choose for
esistors, capacitors, and supply voltages? Apply a signal to the input and observe the signal
at point D, as a function of frequency. Point A is 180° out of phase with the input. At what
frequency is point D in phase with the input? What is the overall gain, from the input to
point D, at this frequency? Careful: The gain at the output of the circuit, at the centre tap of
the potentiometer R, in general is smaller than the gain at point D.
c) Adjust the potentiometer R so that the overall gain to the "output" terminal shown in Figure
1 at the frequency found in Step (b) is about 1. Connect the output to the input. Does the
circuit oscillate? Readjust potentiometer R so that the circuit just barely oscillates.
d) Compare the theoretical frequency and the nominal attenuation of 29 in the RC network
with the values experimentally obtained. Why should there be differences?
e) Set a function generator to approximately the same frequency as that at which the circuit
oscillates. Apply a very small signal, about 10 ?? peak to peak, to the "sync" input of the
oscillator. This will cause the oscillator to synchronise, or lock into the same frequency as the
signal generator. Over how large a range in frequency can you "pull" the oscillator so that it
emains in synchronism with the signal generator? You can also lock on to multiples, or
harmonics of the frequency, especially with a larger input signal.
f) Using Multisim software tool, plot the attenuation and phase shift of the RC network you
designed for Figure 1 from 100 ?? to 10 ???. At what frequency is the gain 1/29? At what
frequency is the phase shift 180°?
g) Assignment Submission
The report should be Word processed, on A4 paper size. Your written report must be submitted to
the Canvas site of the module by the specified deadline on Canvas.
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h) Report Length and Contents
The word limit for the report is 1,500 words (±10%), excluding figure and table captions, equations
and reference list. Write the word count on the title page. The report must include:
• Title page – with module name, report title, candidate number and word count.
• Contents list – with page numbers to include introduction, circuits, testing, e
applications, conclusions and reference list.
• Test and measurement methods – with answer to each question that is highlighted in purple
colour, explanations of what you did and why.
• Circuit design – including calculations and justification of design choices.
• Analysis of results. You should support your report with your circuit diagram and circuit
esponse plots using Multisim software tool.
• Conclusions – containing no new material but summarising what has been achieved.
• Reference list – numbered source details co
esponding to the cross-reference numbers in
i) Assessment Criteria
The following criteria apply:
Mark Range Criteria
An exceptionally well written and presented report which covers all of the criteria
elow and is indicative of individual initiative and originality.
A very well written and presented report, which covers all of the aspects below
and also discusses the background and objectives of the design and shows good
understanding of the circuit design, testing and analysing the resulted circuit.
A well written and presented report which covers all of the aspects below. In
addition, the candidate presents the source e
ors with explanation.
A complete record of the work undertaken with an evaluation of the outcomes.
The account demonstrates that the circuit was co
ectly designed and specified
according to the instruction sheet, that it could be constructed, that the circuit
was tested co
ectly and that its performance was appropriately analysed.
A clear record of the work undertaken and an evaluation of the outcomes. The
account demonstrates that the circuit was designed according to the instructions
sheet, although there may be some e
ors in calculation and simulating the
circuits, that it could be constructed and that the circuit was tested appropriately.
An adequate record of the work undertaken. The account demonstrates that the
circuit was designed according to the instructions sheet and that some progress
was made towards testing the circuit.
There will have been no submission or a seriously inadequate report which
indicate that the project objectives were not addressed.