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ELEC2133
Analogue Electronics
This assignment contributes to 7.5% of the total mark for this course.
The due date is on Tuesday, August 1, 2023 (11:59pm). Assignments are to be
submitted on Moodle before the due date and time. Assignments submitted after
this date will attract a penalty of 5% per day.
The assignment contains one problem with four parts. Each part contains one or
more questions related to the various topics covered related to transistor
amplifiers. Each question has been labelled with P, C, D or HD that indicates the
level of difficulty. P means that the question could be attempted by all students
and students who answer the question correctly are at the level of “pass”. C means
the question could be attempted by students who are at the level of “credit” in the
course. D and HD indicate the question could be attempted by students who are
at the level of “Distinction” and “High Distinction”, respectively.
What does this mean?
If you are targeting to pass or get credit in the course, you may only attempt those
P or C types of questions.
If you are happy or targeting to get a distinction, you can attempt those P, C, and
D types of questions.
If you are targeting a to get high distinction, you should attempt all the questions
including HD type of questions.
Cgs = 4pF and Cgd = 0.2pF
ro = 250KΩ
VA = 200V
QUESTION 1 [60 marks]
Feedback amplifiers are shown in Fig. 4(a) and 4(b). The amplifiers are based on a cascode
amplifier with the first stage implemented by MOSFET and the second stage by BJT. For this
question, assume that the inverting op-amp is ideal in the amplifier of Fig. 4(b).
C4 (very large)
Vs
5V
Vo
1.5k
10k
C2 =20µF
W-1.6V
1M
C1 =10µF
8.8k
3.3k
C3 =20µF
1k
-5V
Y
Z
(W/L = 30)
(W/L = 30)
(W/L = 50)
Q1
Q3
Q2
Q4
0.2k
C5
10k
(very large)
X
(a)
C4 (very large)
Vs
5V
V o
1.5k
10k
C2 =20µF
W-1.6V
1M
C1 =10µF
8.8k
3.3k
C3 =20µF
1k
-5V
Y
Z
(W/L = 30)
(W/L = 30)
(W/L = 50)
Q1
Q3
Q2
Q4
0.2k
C5
10k
(very large)
X
+
-
o
10k
100k
Vo
0.1k
(b)
Fig 1: Feedback amplifiers
Consider Fig. 1(b) for (a)-(h)
(a) [P]Identify the type of feedback topology employed in the amplifier. [3 marks]
(b) [P]Identify and determine the β of the feedback network in the amplifier. [4 marks]
(c) [P,C]Draw the open loop amplifier circuit considering the loading effect of
the feedback networks. [8 marks]
(d) [D] Calculate the mid-band open loop voltage gain of the amplifier. [15 marks]
(e) [P,C] Determine the closed-loop mid-band gain of the amplifier. [5 marks]
(f) [P,C]Calculate the input resistance of the closed-loop amplifier at midband. [5 marks]
(g) [P,C]Calculate the output resistance of the closed-loop amplifier at midband.[5 marks]
(h) [HD,D] Calculate the fH and fL of the feedback amplifier. [10 marks]
(i) [HD,D] What would have happened if the feedback amplifier were applied without the
inverting amplifier as in Fig. 1 (a)? [5 marks]
QUESTION 2 [40 marks]
A Voltage Controlled Oscillator (VCO) based on an astable multivibrator circuit is shown in
Fig. 2. The saturation voltages of the op-amp are +12V and 0V. The multivibrator consists of
a Schmitt trigger and an RC circuit. In the following, use R1=R2=6.8kΩ, R3=20kΩ, R= 7.5kΩ
and C=33nF.
Fig. 2: VCO Astable Multivibrator
(a) [P,C]Draw the input vs output characteristic of the Schmitt trigger. [10 marks]
(b) [D]Determine the frequency of oscillation of the VCO as a function of V. [10 marks]
(c) [D]The multivibrator generates a square waveform. Modify the circuit to generate a
triangular waveform. [10 marks]
(d) [D]Can you suggest a way by which you can convert the circuit in Fig. 2 into a mono
stable multivibrator? Draw the circuit and describe its operation. [10 marks]