Analog Electronics - GATE practice papers - Electronics & Communication

1)   What will be the value of largest MOD ripple counter that can be implemented in order to operate upto 16 MHz using J-K flipflops with tnd = 10 ns?
(Marks : 02)

- Published on 19 Oct 15

a. 8
b. 10
c. 32
d. 64
Answer  Explanation 


According to the given data,

tnd = 10 ns & f = 16 MHz
Assume that 'n' number of flipflops are connected . Hence, the frequency can be expressed as,
f = 1 / n. td
16 x 106 = 1 / (n x 10 x 10 -9 )

n = 1 / 16 x 106 x 10 x 10-9
= 1 / 16 x 10-2
n = 6.25 ≈ 6
Thus, number of flipflops = 6
Number of MOD ripple counters = 2n = (2) 6 = 64

2)   What is the probability of output generation when the inputs are '1' & '0' respectively in S-R clocked flipflop? (Marks : 02)
- Published on 19 Oct 15

a. 1,1 & output remains undefined because outputs try to become '1'
b. 1,0 & flip-flop is reset
c. 0,1 & flip-flop is set
d. 0,0 & output remains unchanged
Answer  Explanation 

ANSWER: 0,1 & flip-flop is set

Set & Reset actions of S-R clocked flipflop are performed only on the basis of a clock pulse. So, when
S=0 & R =0, outputs are 1,1 ( output remains unchanged)
S=0 & R = 1, outputs are 1,0 ( Reset action of flipflop)
S= 1 & R=0, outputs are 0,1 ( Set action of flipflop)
S= 1 & R=1, outputs are 0,0 (output remains undefined since they ought to be 1)

3)   Choose the incorrect statement(s) from the following:

A. MROM does not allow the storage of user specified data to the manufacturer of the memory
B. PROM can be reprogrammed again and again at any number of times
C. EPROM allows to erase the stored content by direct exposure of chip to UV radiations every time before reprogramming
D. E2 PROM allows erasing in an electrical manner despite the exposure of chip to UV rays. (Marks : 02)

- Published on 19 Oct 15

a. A & B
b. C & D
c. Only C
d. B & D
Answer  Explanation 


From the given statements, C & D are correct while A & B are incorrect ones. This is so because

In MROM, the user specified data is absolutely stored to the manufacturer of the memory, while PROM allows the data pattern to be programmed on electrical basis with an assistance of a special device called as PROM programmer. Once the data is programmed in PROM, it cannot be changed.

4)   Which is the correct chronological order of the steps adopted in Quine-Mc Cluskey Method ?

A. Listing of primary implicants

B. Listing of all given minterms in binary equivalent form

C. Arrangement of minterms in accordance to number of '1's

D. Selection of minimum number of primes which covers all the minterms

E. Comparison of each binary number with every term in higher next category at adjacent position. If the difference exists by one position,then check mark is assigned and written in the next column.

F. Repetition of step E for resultant column & continuation of cycle until the occurrence of no further elimination in variables (Marks : 02)

- Published on 19 Oct 15

a. A, B, C, D, E, F
b. C, A, B, F, A, D
c. B , C , E, F, A, D
d. B, A, C,D, E, F
Answer  Explanation 

ANSWER: B , C , E, F, A, D

When the number of variables increases beyond six or multiple form, it becomes very arduous to form the group and simplify the boolean expression.
However, it is possible to overcome this predicament by using Quine-Mc Clusky method for the simplification purpose of the boolean expression.
Therefore, Option (c) specifies the precise sequential order of the steps that are followed or undertaken in this method.

5)   What kind of current sources are applicable for replacing large resistors so as to prevent them from occupying copious areas on IC chip in the voltage regulator circuits? (Marks : 02)
- Published on 19 Oct 15

a. Simple Current Sources
b. Widlar Current Sources
c. Wilson Current Sources
d. Mirror Current Sources
Answer  Explanation 

ANSWER: Widlar Current Sources

Generally, it is mandatory for large resistors to maintain small currents of few micro ampere. Therefore, large areas are occupied by these large resistors on the IC chip. However, Widler current sources are preferred for replacing these large resistors.

6)   Which reasons prohibit /reduce the probability of recombining of charge carriers in the base region of bi-polar junction transistor amplifier? (Marks : 02)
- Published on 19 Oct 15

a. Increase in collector voltage increases the space charge width & decreases base width
b. Increase in emitter voltage increases the space charge width & decreases base width
c. Increase in emitter voltage decrease the space charge width & increases base width
d. Increase in collector voltage decreases the space charge width & increases base width
Answer  Explanation 

ANSWER: Increase in collector voltage increases the space charge width & decreases base width

Due to the phenomenon of early effect, the collector current increases slightly with voltage. This results in the reduction of base current.
However, increase in collector voltage also increases the space charge but reduces effective base-width. Therefore, there is less possibility for recombination within the base region.

7)   Consider the following statements. Which of them represents the precise condition of clipper circuits that clips the input voltage above a reference voltage?

A. If VR> Vi , then diode is supposed to be reversed-biased & hence V0= Vi
B. If Vi> VR , then diode is supposed to be forward-biased & hence V0 = Vi (Marks : 02)

- Published on 19 Oct 15

a. A is false and B is true
b. A is true and B is false
c. Both A & B are true
d. Both A &B are false
Answer  Explanation 

ANSWER: A is true and B is false

Clipper circuits are applicable for selecting that portion of input wave which is located above or below the reference levels.
For the clipper circuit that clips the input voltage above the reference voltage , the necessary operational conditions are

1) If Vi < VR, then diode is reverse-biased & does not operate or conduct Thus, V0= Vi &
2) If Vi>VR , then diode operates in forward biased condition & hence Vo = VR

8)   What is the possible form of output generation in the secondary by the centre-tapped primary of push-pull amplifier due to combination of two collector currents? (Marks : 01)
- Published on 19 Oct 15

a. sine wave
b. square wave
c. cosine wave wave
d. triangular wave
Answer  Explanation 

ANSWER: sine wave

In accordance to the configuration arrangement of push-pull amplifier, the centre-tapped secondary winding of transformer provides equal and opposite voltage to base circuits of the two transistors.
Thus , the supply voltage is connected between bases and centre tap. Transistor T1 provides amplification to every half cycle of the signal by leading it to appear in the upper half of the primary winding of output transformer by the ultimate result of combining two collector currents.
This eventually generates the output in the form of sine wave.

9)   Which current acts as a constant form of current source in an active region of BJT amplifiers? (Marks : 01)
- Published on 19 Oct 15

a. Collector Current
b. Emitter Current
c. Base Current
d. All of the above
Answer  Explanation 

ANSWER: Collector Current

Collector current is independent of collector voltage and depends only on the emitter current in the active region of BJT.
Therefore, the magnitude of collector current is slightly less than that of emitter current because the value of αDC is less than one but, in fact, almost equal to unity.
These reasons enable the collector current to act as a constant form of current source in an active region of BJT

10)   What values of resistance are offered by an ideal diode in forward and reverse biased conditions respectively?(Marks : 01)
- Published on 19 Oct 15

a. zero & infinity
b. infinity & zero
c. zero & unity
d. unity & infinity
Answer  Explanation 

ANSWER: zero & infinity

Ideally, the diode operates in forward-biased condition .This is so because the current flows in forward-biased direction only when the resistance across the voltage is zero. Without any form of obstruction in the flow of current, diodes operates in forward-biasing.
On the contrary, the diode has to pass through an infinite resistance in reverse-biasing mode, which ultimately prevent it from conduction.
However, these both operating conditions of an ideal diode enable it to act as a perfect switch.