Analogue Electronices;

Analogue Electronices;

APPROVED
___________________________________________________________________________________
EXAMINATION PAPER: ACADEMIC SESSION 2011/2012
Campus
Medway
School
Engineering
Department
Engineering Systems
Programme
BEng Engineering Suite
COURSE TITLE
Analogue Electronics
COURSE CODE
ELEE0052
LEVEL
Two
Date and Duration
(incl. reading time)
May 2012, 2 Hours
Paper Set By
Dr R Wu
INSTRUCTIONS TO CANDIDATES
&
INFORMATION FOR INVIGILATORS
The attention of the students is directed to the instructions printed on the
answer book.
Answer THREE of the following four questions.
All questions carry equal marks.
———-
___________________________________________________________________________________
Date & Duration of Exam:
May 2012, 2 Hours
Course Title:
Course Code:
Analogue Electronics
ELEE0052
Page 1 of 7
APPROVED
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Q1.
(a)
If a BJT transistor is operating in the active mode, what is the DC
biasing requirement for the PN junctions?
[4 marks]
(b)
An amplifier circuit is shown in Figure Q1(b).
(i)
What is the role of the resistor RE? Why?
[5 marks]
(ii)
Discuss the role of the capacitor CE in terms of voltage gain.
[5 marks]
+VCC
R1
RS
RC
CC2
CC1
CE
vS
R2
RL
vo
RE
Figure Q1(b)
(c)
In the RC filter shown in Figure Q1(c)(i) (see page 3): R2=R4=1k?,
RL=4.7k?, C1=1µF, C3=0.1µF. The Op-Amp is 741 type. The OpAmp can be modeled as a voltage-controlled voltage source, as shown
in Figure Q1(c)(ii) (see page 3). Ri and Ro are the input and output
resistances, respectively. Ao is the open-loop DC voltage gain. For
µA741 Op-Amps, Ri=2M?, Ro=75?, Ao=2 × 105.
If the input to the filter is a 100mV AC voltage source whose frequency
will be varied between 1Hz and 1MHz logarithmically with
100 points-per-decade, write the PSPICE input file to calculate the
frequency response of this filter. (In the Op-Amp model, a DC voltage
source with V=0 can be connected between node 1 and the ground to
simulate the grounded non-inverting terminal).
[11 marks]
Cont’d…..
___________________________________________________________________________________
Date & Duration of Exam:
May 2012, 2 Hours
Course Title:
Course Code:
Analogue Electronics
ELEE0052
Page 2 of 7
APPROVED
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Question 1(c) Continued.
C3
C1
R4
R2
vi
RL
vo
Figure Q1(c)(i)
5
2
vd
Ri
Ro
3
Aovd
vo
0
1
Figure Q1(c)(ii)
___________________________________________________________________________________
Date & Duration of Exam:
May 2012, 2 Hours
Course Title:
Course Code:
Analogue Electronics
ELEE0052
Page 3 of 7
APPROVED
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Q2.
(a)
Figure Q2(a) shows a differential amplifier fed by a common-mode
voltage signal vCM. If the output is taken single ended, assuming
R>>rbe, ß/(ß+1)˜1, derive the voltage gain vc1/vCM or vc2/vCM by using
the concept of the common-mode half-circuit.
[10 marks]
VCC
RC
RC
vc 1
vc2
Q1
v
Q2
v
CM
R
CM
I
-VEE
Figure Q2(a)
(b)
In the differential amplifier shown in Figure Q2(b) (see page 5),
RC=5.1k?, R=100k?, I=1mA, ß=145.
(i)
What is the requirement for Q1 and Q2 in semiconductor device
manufacturing? What is the role of the current source I?
[5 marks]
(ii)
Determine the input differential resistance Rid.
[4 marks]
(iii)
Determine the differential-mode gain Ad.
[3 marks]
(iv)
Determine the common-mode rejection ratio (CMRR) in dB.
[3 marks]
Cont’d…..
___________________________________________________________________________________
Date & Duration of Exam:
May 2012, 2 Hours
Course Title:
Course Code:
Analogue Electronics
ELEE0052
Page 4 of 7
APPROVED
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Question 2(b) Continued.
VCC +5V
RC
RC
Vo
Q1
Q2
Vi
R
I
VEE -5V
Figure Q2(b)
___________________________________________________________________________________
Date & Duration of Exam:
May 2012, 2 Hours
Course Title:
Course Code:
Analogue Electronics
ELEE0052
Page 5 of 7
APPROVED
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Q3.
(a)
How to determine the type of feedback in terms of the gain of a
system?
[3 marks]
(b)
In the common-emitter amplifier shown in Figure Q3(b): Rs=4k?,
R1=10k?, R2=5k?, RE=1k?, RC=2k?, RL=5k?, VCC=12V. The
transistor parameters are: ß=100, Cp=10pF, Cµ=2pF.
(i)
In this amplifier, the gain falloff in the high frequency band is
due to the effects of which capacitors?
[3 marks]
(ii)
Find its DC equivalent circuit, and hence determine IC, VB,
VC and VE.
[7 marks]
(iii)
Find the small signal equivalent circuit (gm, rp) for the
transistor, and hence determine the midband gain.
[5 marks]
(iv)
Find its high-frequency equivalent circuit. Use the miller-effect
method to determine the total input capacitance and hence the
upper 3-dB frequency fH (the dominant high-frequency).
[7 marks]
+VCC
R1
Rs
CC2
RC
CC1
CE
Vs
R2
RL
RE
Figure Q3(b)
___________________________________________________________________________________
Date & Duration of Exam:
May 2012, 2 Hours
Course Title:
Course Code:
Analogue Electronics
ELEE0052
Page 6 of 7
APPROVED
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Q4.
(a)
An amplifier shown in Figure Q4(a) is intended to supply a voltage to
floating loads (those for which both terminals are ungrounded) while
making greatest possible use of the available power supply. Assuming
that ideal Op-Amps are used;
(i)
Determine its voltage gain: vo/vi.
[10marks]
If R1=10k?, R2=5k?, R3=15k?, what is the voltage gain?
Sketch the output voltage waveform vo for a 1V peak-to-peak
sine wave applied at A.
[8 marks]
(ii)
R2
R1
B
R1
A
v?
R3
R1
v?
R1
C
Figure Q4(a)
(b)
For the Wien-bridge oscillator shown in Figure Q4(b).
(i)
If C=0.01µF, what is the value of R to generate an oscillation
frequency of fo=10kHz?
[4 marks]
(ii)
If R2=10k?, determine the value for R1.
[3 marks]
R2
R1
Vo
R
Vi
R
C
C
Figure Q4(b)
___________________________________________________________________________________
Date & Duration of Exam:
May 2012, 2 Hours
Course Title:
Course Code:
Analogue Electronics
ELEE0052
Page 7 of 7

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