Roll No.: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Amrita Vishwa Vidyapeetham
Amrita School of Engineering, Coimbatore
B.Tech. Degree Examinations – August 2022
Fourth Semester
(Electronics and Communication Engineering)
19ECE212 Linear Integrated Circuits
Time : Three hours
Maximum : 100 Marks
CO
Course Outcomes
CO01
CO02
CO03
CO04
Able to understand the construction of electronic systems using operational amplifiers
Able to understand the various specification parameters of op-amp
Able to design and analyze linear and non-linear circuits with op-amps
Able to design and analyze sinusoidal oscillator circuits
Instructions:
1. Answer all questions in the order in which they appear.
2. All circuit diagrams / figures are to be drawn neatly and labelled, using pencil.
3. All components used may be considered to be ideal, unless specifically mentioned otherwise.
4. The following may be assumed: 𝑉𝑇 = 25 𝑚𝑉.
5. Any opamps used, may be considered to be powered off + 15 V supplies, unless mentioned
otherwise.
6. Any variables / parameters used, if not explained, may be considered to have the same
significance as those used in Microelectronic Circuits – Theory and Applications, by Sedra &
Smith, 5th ed.
1.
Fill in the blanks with the most appropriate answer. Only the answer needs to be noted
down in the answer sheet.
[15]
[CO1, CO2,CO3,CO4] [BTL2]
(i) For an inverting amplifier, keeping the feedback resistance a constant, if the input
resistance is to decrease, the gain will -----------.
(ii) For a difference amplifier of unity gain, with the resistances = R, the differential mode
input resistance is ------------.
(iii) If the NE555 timer IC were to be powered by a 15 V source, the voltage reference levels
would be ------------- V and ------------ V.
(iv) A comparator is designed to operate in the ----------- region of the Voltage Transfer
Characteristic (VTC).
(v) A Schmitt Trigger provides noise immunity by means of the -----------------, provided by
the circuit.
(vi) The time period of an astable multivibrator with a duty cycle of 25%, a feedback factor
of 75% and a time constant of 1 ms, is -------------- s.
(vii) A unity gain amplifier was found to have a bandwidth of 1.5 MHz. If the same amplifier
were to be re-configured for a bandwidth of 50 kHz, its closed loop voltage gain would
be ---------.
(viii) The input offset current of an operational amplifier is defined as 𝑖𝑜𝑠 = ----------.
(ix) If an amplifier with gain 𝐴 and negative feedback 𝑘, is to oscillate, the condition to be
satisfied is that --------------.
Page 1/6
(x) The input resistance of an instrumentation amplifier, with ideal opamps, is ----------.
(xi) The typical output resistance of the 𝜇𝐴741 is ----------------------.
(xii) In a typical inverting amplifier using an opamp, a ------------- is sampled and a ------- is
mixed at the input.
(xiii) The Schmitt Trigger has ------------- stable state(s).
(xiv) Employing negative feedback, if the output voltage were to be sampled, the output
impedance -----------.
(xv) The output impedance of a BJT based current mirror is due to the -----------------.
2.
Match the entries in Column A against those in Column B. Write down only your choices
in the answer sheet.
[10]
[CO1, CO2,CO3,CO4] [BTL2]
A
(i)
(ii)
B
Inverting amplifier
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
(j)
(k)
(l)
(m)
(n)
(o)
vi = 1 V
Fig. 1
(iii)
(iv)
(v)
(vi)
(vii)
(viii)
(ix)
(x)
3.
Non-inverting Comparator
Schmitt Trigger
Slew Rate of an opamp
Negative feedback
RC Phase Shift Oscillator
Log Amplifier
Superdiode
Astable Multivibrator
𝑓𝑜 =
1
2𝜋√6𝑅𝐶
15 𝑉; 𝑣𝑖 > 𝑉𝑅
𝑣𝑜 = ⌊
−15 𝑉 𝑣𝑖 < 𝑉𝑅
Prevents opamp from saturating
Bistable Multivibrator
Increases the bandwidth
Expansion
Compression
Increases the output impedance
Relaxation Oscillator
Voltage Sampling, Voltage mixing
vo = |vi|
𝑣𝑜 = 𝑣𝑖
Large Signal Parameter
−15 𝑉; 𝑣𝑖 > 𝑉𝑅
𝑣𝑜 = ⌊
15 𝑉
𝑣𝑖 < 𝑉𝑅
Voltage Sampling, Current mixing
Choose the correct answer from amongst those given. Please note down clearly and legibly
only your choice. For example, if your answer to question 3(i) is “None of these”, write down
“(e)”.
[15]
[CO1, CO2,CO3,CO4] [BTL2]
(i) For a difference amplifier with inputs V1 and V2, if the output vo is given by the
expression, 𝑣𝑜 = 10𝑉1 − 9.99𝑉2 , then the CMRR of the amplifier (in dB) is
(a) 40
(b) 50
(c) 60
(d) 80
(e) None of these
(ii) Given a non-inverting Schmitt Trigger of upper and lower voltage levels of 2 V and
1.8 V respectively, the reference voltage (VR) required would be (in V)
(a) 1.95
(b) 2.05
(c) 0.87
(d) 1.85
(e) None of these
(iii) The 1N4007 diode with a cut-in voltage (Vγ ) of 0.6 V, is used
R
in a super-diode configuration, such that the output, 𝑣𝑜 =
vo
R + 0.1𝑆𝑖𝑛(2 ∗
0; 𝑣𝑖 < 0. If the input to the circuit were 𝑣𝑖 = [0.2
𝜋 ∗ 100𝑡)]𝑉, the average value of the output would be (in V)
v
vi
o
10 k
90 k
(a) 0.2
(b) 0.4
(c) 0.127
(d) 0.064
(e) None of these
Fig. 2
v
i
1
k

9
k

Page 2/6
(iv) If the resistor R in Fig. 2 is provided for the purpose of input bias current compensation,
its value is likely to be (in kΩ)
(a) 1
(b) 9
(c) 10
(d) 0.9
(e) None of these
(v) In a common-emitter amplifier, if an emitter resistance of 100 Ω is added, the input
resistance of the amplifier
(a) Decreases (b) Increases (c) is not affected
(d) changes, depending on the
nature of the BJT
(e) None of these
(vi) If the time period for which the output of an astable multivibrator remains high is
indicated by TON, then TON depends on (i) the time constant, RC; (ii) the feedback
network; (iii) the supply voltage levels, + VCC; (iv) the voltages to and from which the
capacitor charges and discharges. Which of these four statements are true ?
(a) (i), (ii) and (iii)
(b) (ii), (iii) and (iv)
(c) (i), (iii) and (iv)
(d) (i), (ii), (iii) and (iv)
(e) None of these.
5.6 𝑉; 1 𝑉 < 𝑣𝑖 < 3 𝑉
(vii) A circuit has the VTC given by 𝑣𝑜 = [
]. If the input to the circuit
−5.6 𝑉;
𝑒𝑙𝑠𝑒𝑤ℎ𝑒𝑟𝑒
vi is given by 𝑣𝑖 = 5 ∗ 𝑆𝑖𝑛(2 ∗ 𝜋 ∗ 0.1𝑡), the output vo at t = 4.2 s is (in V)
(a) 0
(b) 5.6
(c) -5.6
(d) vi
(e) None of these
(viii) In an astable multivibrator, when the output levels change between + 3.3 V, the capacitor
of 10 nF charges between + 1 V, through a resistor of 10 kΩ. Then, the time period of
the output waveform would be (in μs)
(a) 62.6
(b) 125.1
(c) 100.3
(d) 52.4
(e) 55.3
(ix) In a current amplifier, employing negative feedback, the output impedance ------, while
the input impedance --------.
(a) Decreases, Decreases
(b) Increases, Increases
(c) Increases, Decreases
(d) Decreases, Increases
(e) None of these
When the inputs to a difference amplifier were 20 mV and -20 mV, its’ output was found
to be 500 mV and 490 mV, when the inputs were 1.02 V and 0.98 V. Its’ CMRR is (in
dB)
(a) 62
(b) 42
(c) 71
(d) 56
(e) None of these
(xi) For a monostable multivibrator, the frequency of the output signal is related to that of
the trigger as
(a) They are equal
(b) The trigger frequency is greater than that of the output
(c) The trigger frequency is lesser than that of the output
(d) The trigger frequency is not related to that of the output
(e) None of the above
−3𝑣 ;
𝑣𝑖 > 0
(xii) The VTC of a circuit is given by the expression, 𝑣𝑜 = [ 0; 𝑖 𝑒𝑙𝑠𝑒𝑤ℎ𝑒𝑟𝑒
. The circuit is
(x)
likely to be a(an)
(a) Inverting amplifier
(b) Window Comparator
(c) Schmitt Trigger
(d) Precision Full Wave Rectifier
(e) None of these
(xiii) The slew rate of the 𝜇𝐴741 operational amplifier is typically ------------ (in 𝑉/𝜇𝑠).
(a) 0.5
(b) 1.2
(c) 0.2
(d) 0.3
(e) 0.8
Page 3/6
(xiv) If the differential gain of a difference amplifier with a CMRR of 80 dB is 10, the
common mode gain would be ----------------.
(a) 10−3
(b) 10−2
(c) 103
(d) 102
(e) None of these
(xv) Pick the odd man out: 𝜇𝐴741, 𝑂𝑃07, 𝑇𝐿064, 𝑇𝐿071, 𝐿𝑀311.
(a) 𝜇𝐴741
(b) 𝑂𝑃07
(c) 𝑇𝐿064
(d) 𝑇𝐿071
(e) 𝐿𝑀311
For questions 4 - 13, note down your answer to the question. There will be NO partial credit.
[10*2 = 20 marks]
[CO1, CO2, CO3,CO4] [BTL3]
4.
For the circuit shown in Fig. 3, with 𝑉1 = 1 𝑉; 𝑉2 = 2 𝑉; 𝑅 = 10 𝑘Ω and 𝑉𝑅 = 10 𝑉, neatly plot its’
Voltage Transfer Characteristic. Determine the current flowing through the 10 𝑘Ω resistor,
when 𝑣𝑖 = 2.5 𝑉.
5.
In Fig. 4, 𝑅1 = 𝑅3 = 10 𝑘Ω; 𝑅2 = 100 𝑘Ω and 𝑅4 = 99 𝑘Ω. If 𝑉1 = 1.1 𝑉 and 𝑉2 = 1 𝑉, determine 𝑣𝑜
(rounded off to two decimal places).
6.
If, for the circuit shown in Fig. 5, 𝑅 = 1 𝑘Ω, 𝑣𝑖 = 𝑆𝑖𝑛(𝜔𝑡), 𝑓 = 100 𝐻𝑧, determine the output 𝑣𝑜 ,
at t = 2.5 ms.
Fig. 3
7.
Fig. 5
Fig. 4
A non-inverting amplifier of gain 10 is found to have a bandwidth 150 kHz. If the amplifier
is now re-configured to have a gain of 25, what will be the bandwidth ?
Fig. 6
Fig. 7
Fig. 8
8.
(i) Obtain an expression for the output 𝑣𝑜 of the circuit shown in Fig. 6. It is given that 𝑅 =
1 𝑘Ω; 𝐶 = 1 𝜇𝐹. (ii) If 𝑉1 = 1 𝑉; 𝑣𝑖 = 2 𝑉, then, determine 𝑣𝑜 , at time 𝑡 = 1 𝑚𝑠.
9.
(i) For the circuit of Fig. 7, obtain an expression for the output 𝑣𝑜 . (ii) If 𝑅1 = 𝑅2 = 10 𝑘Ω, 𝑉1 =
0.5 𝑉 and 𝑣𝑖 = 0.5𝑡, what is the output 𝑣𝑜 at 𝑡 = 1 𝑠 ?
10. Consider the circuit given in Fig. 8. 𝑅1 = 5 𝑘Ω; 𝑅2 = 10 𝑘Ω; 𝑅3 = 65 𝑘Ω; VR = 0 𝑉 and 𝐶 = 100 𝑛𝐹.
Plot the output waveform and determine its period.
Page 4/6
11.
Fig. 11
Fig. 10
Fig. 9
The current (𝐼𝐷 ) – voltage (𝑉𝐷 ) relationship of the diode in the circuit of Fig. 9 is given by
𝑉𝐷
𝐼𝐷 = 𝐼𝑆 𝑒 𝑉𝑇 , where 𝐼𝑆 = 1 𝑝𝐴. If 𝑅1 = 1 𝑘Ω, 𝑉𝑅 = 0.5 𝑉 and 𝑣𝑖 = 1 𝑉, determine 𝑣𝑜 (rounded off to one
decimal place).
12. The opamp of the circuit in Fig. 10 has an open-loop gain of 40. If 𝑅1 = 1 𝑘Ω; 𝑅2 = 9 𝑘Ω and
𝑣𝑖 = 0.2 𝑉, determine 𝑣𝑜 .
13. If the output 𝑣𝑜 of the circuit of Fig. 11 is 0.42 V, with 𝑅1 = 100 Ω and 𝑅2 = 560 𝑘Ω, then, the
input offset voltage of the opamp is ------------------.
Each question from 14 to 17 carries 5 marks and should begin on a fresh page. There WILL
be partial credit.
[4*5 = 20 marks]
[BTL3]
14.
Consider the circuit shown in Fig. 12. If the opamp can be considered to be ideal, with the
zener diodes (𝐷1 & 𝐷2 ) having a zener voltage VZ = 3.3 V and a forward cut-in voltage Vγ =
0.7 V, plot the voltage transfer characteristic of the circuit. Mark the cardinal points. [CO3]
vi
2 k
9 k
vo
D1
2 k
D2
1V
Fig. 12
15.
Plot the steady-state waveforms at VP, VN and vo for the circuit shown in Fig. 8. Clearly mark
all salient voltages and time intervals. It is given that 𝑅1 = 1 𝑘Ω; 𝑅2 = 9 𝑘Ω; 𝑅3 = 10 𝑘Ω; 𝑉𝑅 = 1 𝑉
and 𝐶 = 10 𝑛𝐹. It is known that the output levels of the opamp are +13 V and -12 V.
[CO3]
16.
(i) Identify the circuit shown in Fig. 13. (ii) The current source is such 1 𝜇𝐴 < 𝐼𝐴 < 10 𝑚𝐴. It
Fig. 13
was found that when 𝑉𝑅 = 1 𝑉, 𝐼𝐴 = 1𝜇𝐴, the output 𝑣𝑜 = 0.5 𝑉. Determine the output for 𝐼𝐴 =
10 𝑚𝐴.
[CO3]
Page 5/6
17.
The circuit of Fig. 14 is required to oscillate at a frequency of 10 kHz. (i) If 𝐶 = 10 𝑛𝐹, what
should be the value of R ? (ii) If 𝑅1 = 10 𝑘Ω, what should be the minimum value of 𝑅2 , for
oscillations to be sustained ?
[CO4]
Fig. 14
Questions 18 and 19 each carry 10 marks and should begin on a fresh page. There WILL be
partial credit.
[BTL4]
18.
(i) Design a circuit to produce a single positive pulse of duration 100 𝜇𝑠. The circuit is
normally in the OFF state.
(ii) If provided with a pulse train of period 10 ms, with a duty cycle of 10%, develop a circuit
to provide the necessary input to shift the circuit of (i) to the unstable state. Justify any
assumptions that you make.
[CO1, CO3]
19.
A differential pressure transducer provides a differential output voltage (𝑉𝑜 ) given by the
expression 𝑉𝑜 = (100 + 0.3 𝛿𝑃) mV, where 𝛿𝑃 is the differential pressure to be measured, in
mmHg. If 𝛿𝑃 varies between 100 and 350 mmHg, design a circuit which will provide
maximum common mode suppression and an output linear with 𝛿𝑃, with a sensitivity of 10
mV/mmHg. Minimum component spread is to be ensured. An alarm is to be raised when the
pressure rises above 300 mmHg – a red LED, with a cut-in voltage of 1.8 V is to light up to
indicate this status. If the maximum current through the LED is to be 10 mA, design an
appropriate circuit for this purpose, so that the output voltage will not be greater than 5 V.
Justify the use of any component and any assumptions that you make. You are provided with
ideal components and power supplies of + 10 V.
[CO1, CO2, CO3]
Course Outcome / Bloom’s Taxonomy Level (BTL) Mark Distribution Table
CO
CO01
CO02
CO03
CO04
Marks
37
18
37
8
Average BTL
BTL
1
2
3
4
Marks
0
40
40
20
2.8
Page 6/6