## Analogue Electronices;

Analogue Electronices;

APPROVED
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Campus
Medway
School
Engineering
Department
Engineering Systems
Programme
BEng Engineering Suite
COURSE TITLE
Analogue Electronics
COURSE CODE
ELEE0052
LEVEL
Two
Date and Duration
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 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)
[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
___________________________________________________________________________________
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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