Analogue Electronics (EO127)
s
School of Computing, Engineering and Mathematics
Division of Engineering and Product Design
Semester-Two Examinations, May/June 2011
B.ENG. HONOURS DEGREE & FD.ENG.
ANALOGUE ELECTRONICS - PART B (EO127)
EXAMINER: DR. D.S. GILL
Instructions to Candidates:
 The time allowed is THREE hours
 Attempt any FOUR questions only
 The total number of questions is SIX
 Each question carries 25 marks
 This is a CLOSED-BOOK examination
Special Requirements:
 Appendix 1 - Blank Oscilloscope Screens for Question 1
 Linear graph paper
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Analogue Electronics (EO127)
Question 1
(a) A general-purpose dual-channel oscilloscope displays two ‘triangular waves’ of
the same frequency, but different phase on channel A and channel B, as shown
in Figure Q1. The setting of the timebase control is 0.2 μs/division and the Ysensitivity is set to 0.5 V/division.
A
B
Figure Q1
(i)
Estimate the phase difference between the two waveforms, assuming that
channel A is used as a reference for phase. You should include all
justification as to how you arrived at the answer and whether it is leading or
lagging.
(6 marks)
(ii) Estimate the peak-to-peak amplitude of the signal on each channel. You
should include all justification as to how you arrived at the answer.
(4 marks)
(b) You are required to organise the test equipment in a laboratory. You require a
split supply of ±12 V and a common ground. However, you only have two single
12 V power supply units. Show, with justification and appropriate diagrams, how
you can use these units to meet the power supply requirements.
(5 marks)
(c) Sketch the waveforms of two sinewave signals, A and B, using the copy of the
oscilloscope screen found in the appendix at the end of this examination paper.
You should show all working for your answer.
Signal A has an RMS value of 1 V.
Signal B has a peak-to-peak amplitude of 2 V.
Signal B leads Signal A by 90º. The frequency of both signals is 1 kHz.
You may choose your own settings for the timebase control and the Ysensitivity. However, it is essential that you state what settings you have
chosen in your answer. Ensure that you write your student number on the top
right-hand side of the sheet and attach it to your answer script.
(10 marks)
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Analogue Electronics (EO127)
Question 2
(a) (i)
Define the terms “Bode Plot” and “Decibel” in the context of a voltage
amplifier’s frequency response.
(4 marks)
(ii) The following are voltage gains of a particular circuit at different
frequencies:
10,
1, 0.1, 0.707
Express each of the above in decibels. You should show all your working.
(4 marks)
(iii) What is the significance of the gain value of 0.707?
(2 marks)
(b) (i)
Sketch the circuit diagram of a simple non-inverting linear scaling
operational amplifier configuration to be used with a power supply of ±15 V.
Include all resistor values, selected from the E12 series, in order to produce
a nominal gain of 15. One of the resistors used should be 180 kΩ. You
should show all your working.
(5 marks)
(ii) Determine the tolerance on the gain of your circuit if the resistors have a
tolerance of ± 3%.
(3 marks)
(iii) In practice what is the maximum input voltage that you would apply to the
amplifier. Give reasons to support your answer.
(2 marks)
(iv) State the phase difference between output and input signals when the
amplifier voltage gain is 0.707.
(1 mark)
(v) Show what changes are needed to your circuit so that it produces instead a
gain of -15. Include all justification for your answer and appropriate
diagrams.
(4 marks)
Note: the following are numbers used in the E12 series:
1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2 and 10.0
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Analogue Electronics (EO127)
Question 3
(a) Sketch a block diagram of a ‘basic instrumentation system’ that converts a
measurand from the ‘real world’ into a ‘signal’ that can be displayed and/or
recorded. Explain the role or function of each block.
(8 marks)
(b) Transducers can be classified by their transduction method or by the parameter
that they are designed to measure. You are required to list three for the
transduction method and three for parameter measurements.
(6 marks)
(c) What is a LVDT? Illustrate your answer with suitable diagrams.
Explain how an LVDT works and give an example of an application.
(11 marks)
Question 4
(a) In the context of the digitisation process of an analogue sound signal, explain
briefly what is meant by each of the following:
(i)
Sampling
(2 marks)
(ii) Nyquist rate
(2 marks)
(iii) Quantisation
(3 marks)
(iv) Pulse Code Modulation
(2 marks)
Your answer should be supported by appropriate diagrams and explanations.
(b) Using a simplified version of a four-rung R-2R Ladder Digital-to-Analogue
Converter (DAC), prove that the currents flowing through the ‘rungs’ (I1, I2, I3, I4)
have magnitudes that relate to one another in a ‘binary-weighted’ sequence.
Ensure that all steps of the analysis are justified.
(9 marks)
(c) Use the ‘Successive Approximation’ algorithm to perform conversion of an
analogue voltage value of 2.49 V to an 8-bit digital word. The significance of the
‘Least Significant Bit (LSB)’ should be 10 mV. Use an appropriate table to
structure your answer.
(7 marks)
Page 4 of 8
Analogue Electronics (EO127)
Question 5
(a) Sketch the gain-frequency response of a low-pass filter, a high-pass filter and a
notch-filter. Hence explain what is meant by the following terms:




bandwidth
mid-band gain
low-frequency breakpoint
high-frequency breakpoint
(9 marks)
(b) (i)
Referring to the circuit shown in Figure Q5, and taking care to include every
step, prove that the voltage gain Vout/Vin can be expressed as follows:
Vout

Vin
k
1 j

H
where:
k
R2
,
R1  R2
H 
R1  R2
C2 R1 R2
R1
50 
Vin
Vout
C2
0.01 F
R2
600 
Figure Q5
(10 marks)
(ii) Using the given values of the components in Figure Q5 above, determine
with full justification the value of the frequency when the voltage gain falls to
0.707 of the mid-band gain.
(6 marks)
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Analogue Electronics (EO127)
Question 6
(a) (i)
A mixer circuit is required to combine three signals, V1, V2 and V3 into a
single signal, V4, so that it can be fed to the input of a pre-amplifier. Show
how a summing amplifier, using an operational amplifier, can be used to
implement this design. Your answer will include a sketch of the required
circuit configuration.
(5 marks)
(ii) Assuming that the input signals, V1, V2 and V3, are to be mixed equally,
derive an expression for the output signal of the mixer circuit V4 in terms of
the input signals and the passive components used.
(9 marks)
Your answer should include all working and assumptions made.
(b) For Figure Q6, derive from first principles, the mathematical expression for
V2/V1, showing all working and stating any assumptions made. Hence state its
purpose.
VC
i2
C
i1
-
R1
Node X
V1
+
V2
Figure Q6
(11 marks)
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Analogue Electronics (EO127)
Attach to your answer script if used.
Student Registration number: ___________________
Appendix 1 – Oscilloscope screen for Question 1.
SPARE COPY BELOW
Please ensure that you attach this sheet to your answer book.
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Analogue Electronics (EO127)
Version 110406.1 dsg
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