Indian Institute of Space Science and Technology
Department of Avionics
AV 211 Analog Electronic Circuits
End Semester Examination
Time: 3 hours Max. marks: 50
There is a choice between Qn. 4 & Qn. 5 and between Qn. 7 &
(On. 8. All other questions are compulsory.
1. It is required to design a Class B power allil)lifier to deliver an average
output power of 2()Wto an 80 load. The power supplies are to be
selected such that they are about,5V greater than the peak output
voltage. (You can consider a sinusoidal signal.) This avoids transistor
saturation and the associated non-lineardistortion. Tlie amplifier runs
on bipolar supply.
(a) Determine the power supply voltages required (to the nearest volt
in the appropriate direction (2 marks)
(b) Determine the peak current drawn from each supply while deliv-
ering 20 W to the load. (1 mark)
(c) What, is the total supply power drawn when the amplifier supplies
a power of 20W to the load? You can assume ideal Class-B opera-
tion. (The DC fourier component of a halfrwave rectified sinewave
of amplitude A is A/T.) (2 marks)
(d) Calculate tlle efficiencycorresponding to a '20W output. (1 Illark)
(e) Draw the complete circuit and add suitable elements to provide
short circuit protection and thermal stability and provide the com-
ponent values. You can assume that the transistor turns on at
4A Explain how the short-circuitprotection and thermal sta-
bility are achieved by your design. (2 marks)
(f) When the transistor turn-on voltage of 0.6V is considered, sketch
the waveformsof the input voltage,emitter currents and output
voltage. Define cross-over distortion. (2 Illarks)
2. Consider two signals (t) 2 + 0.7 + 0.004sin(2T2900t)
and (t) 2+0.7 sin(2T50t) —0.004sin(2T2900t)+ 0.01 sin(2T3500t).
MJritedown the differential signal colliponellts and tlle colli111011
Inode
signal components. (2 marks)
3. Design an op-allil) RC low pass filter with a low frequency gain of close
to 2b V/ V with a cut-off frequency of around 20 kHz. You are required
1
(provided at the
1 only
to choosestandard resistor valuesfrom Figure values are
470nF,
capacitor
end of the question paper). The available With these
compo-
0.01 nF.
100nF, 47nF, 10nF, 4.7nF, lnF, 0.1nF,
that you obtain? (5
nents, what is the actual gain and 3-dB frequency
marks)
Derive the loop gain L(s), L(jw), the
4. Consider the circuit shown below.
RI for sustained os-
frequency at which the phase is 0, the required IRO/
cillations. (10 marks)
OR
5. Draw the circuit of a Colpitts oscillator. Draw the equivalent circuit
diagram and derive the conditions for oscillations and the frequency
of oscillation. You may neglect Cit and of the BJT for simplifiecl
analysis. (10 marks)
6. A pulse of 10ms is required to be generat,ed using a 555 timer, every time
a trigger occurs. The trigger goes from Vcc to OVfor a brief period
of time. Design a suitable circuit for the same. Draw the complete
circuit. Derive the expressionsfor the time period. Use resistors only
from the standard resistor values in Figure 1, provided at the end of the
question paper. The available capacitor values are 47/JF, 4.7/-117,
IVF, 470nF, IOOnF, 47nF, 10nF, 4.7nF, lnF. Using these
components,
what is the actual time period that you obtain? (8 marks)
7. For the circuit given below, take a 0.99. Draw the complete
small
signal circuit. What is the input resistance Rin? Derive and
calculate
the overall gain (8 marks)
2
12 kO Re
(21 12 kO
750
sig
OR
8. Consider the circuit shown below. Draw the small signal equivalent
circuit and derive the gain X and the gain X. (8 nnarks)
x
z
9. An opamp is said to have an input bias current of 100nA with an
input offset current of 8nA. The opump's offset voltage is measured to
12 The datasheet, specifies an open loop gain of 105 with a gain
banclwidth procluct of 10 MHz. Define each of these terrns and illustrate
3
them in terms of the terminal characteristics(voltages or currents at
each terminal as applicable) of an opamp. (3 marks)
10. Draw an ideal integrator using opamp and derive its transfer function.
What is the drawback of it? How is a real integrator designed using
an opamp? Derive its transfer function and comment on the choice of
components that will make it as closeto an ideal integrator. Compare
the frequency response of the two designs. (4 marks)
Standard Resistor Values
1.0 10 100 100K 1.0M
1.1 11 110 1.1K I IOR 1.1M
1.2 12 120 12k 120K 1.2M
1.3 IS 1.3K 13k
1.5 150 1.5K
1.6 16 160 16K 1601<
1.8 IS ISM
2.0 2.0K 20k
2.4 24 240 2.4K
2.7 270 27K 270K 2.7M
3.0 300 3.0K 300k 3.0M
3.3 33 3.3K 33K 330K 3.3M
3.6 36 360 3.6K 36k 360K 3.6M
3.9 390 39K 390K 3.9M
4.3 430 4.3K 43 430K
4.- 470 4-1k 4.7M
51 5.1K 51K
560
6.2 62 620 6.2K 62k 620K 6.2M
6.8 680 6.SR 6SOR 6.8M
7.5 7.5K
82.2 820 S.2K S2R 820K 8.2M
9.1 91 910 9.1K 91K 910K 9.1M
Figure 1: Standard resistor values
