EC GATE 2011 (Test 5)



Tag: ec gate 2011
Q.1
The horse has played a little known but very important role in the field of medicine. Horses were injected with toxins of diseases until their blood built up immunities. Then a serum was made from their blood. Serums to fight with diphtheria and tetanus were developed this way. It can be inferred from the passage that horses were
A. given immunity to diseases
B. generally quite immune to diseases
C. given medicines to fight toxins
D. given diphtheria and tetanus serums
Answer : Option B
Explaination / Solution:

Option B fits the sentence, as they built up immunities which helped humans create serums from their blood.

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Q.2
The logic function implemented by the circuit below is (ground implies logic 0)

A. F = AND (P, Q)
B. F = OR (P, Q)
C. F = X NOR (P, Q)
D. F = X OR (P, Q)
Answer : Option D
Explaination / Solution:



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Q.3
The circuit below implements a filter between the input current ii and the output voltage v0. Assume that the opamp is ideal. The filter implemented is a

A. low pass filter
B. band pass filter
C. band stop filter
D. high pass filter
Answer : Option D
Explaination / Solution:

From diagram we can write 

Transfer function


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Q.4
In the circuit shown below, for the MOS transistors, and the threshold voltage VT = 1 V. The voltage Vx at the source of the upper transistor is

A. 1 V
B. 2 V
C. 3 V
D. 3.67 V
Answer : Option C
Explaination / Solution:

Given circuit is shown below.

For transistor M2,

Since   thus M2 is in saturation. By assuming M1 to be in saturation we have

Taking positive root,

 Thus our assumption is true and Vx = 3 V.


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Q.5

The bias current IDC through the diodes is
A. 1 mA
B. 1.28 mA
C. 1.5 mA
D. 2 mA
Answer : Option A
Explaination / Solution:

The current flows in the circuit if all the diodes are forward biased. In forward biased there will be 0 7. V drop across each diode.


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Q.6
A transmission line of characteristic impedance 50 W is terminated in a load impedance ZL. The VSWR of the line is measured as 5 and the first of the voltage maxima in the line is observed at a distance of λ/4 from the load. The value of ZL is
A.
B. 250Ω
C. (19.23 + j46.15)Ω
D. (19.23 - j46.15)Ω
Answer : Option A
Explaination / Solution:

Since voltage maxima is observed at a distance of λ/4 from the load and we know that the separation between one maxima and minima equals to λ/4 so voltage minima will be observed at the load, Therefore load can not be complex it must be pure resistive.

 also RL = R0/s (since voltage maxima is formed at the load)
 R= (50/5)Ω


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Q.7
A four-phase and an eight-phase signal constellation are shown in the figure below.

Assuming high SNR and that all signals are equally probable, the additional average transmitted signal energy required by the 8-PSK signal to achieve the same error probability as the 4-PSK signal is
A. 11.90 dB
B. 8.73 dB
C. 6.79 dB
D. 5.33 dB
Answer : Option D
Explaination / Solution:

Here Pe for 4 PSK and 8 PSK is same because Pe depends on d . Since Pe is same, d is same for 4 PSK and 8 PSK.
Additional Power SNR



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Q.8
Two systems H1(Z) and H2(Z) are connected in cascade as shown below. The overall output y(n) is the same as the input x(n) with a one unit delay. The transfer function of the second system H2(Z)is

A.
B.
C.
D.
Answer : Option B
Explaination / Solution:



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Q.9
An input   is applied to an LTI system with impulse response h(t) = u(t). The output is
A. [1 - exp (-2t)] u(t) + u(t + 6)
B. [1 - exp (-2t)] u(t) + u(t - 6)
C. 0.5 [1 - exp (-2t)] u(t) + u(t + 6)
D. 0.5 [1 - exp (-2t)] u(t) + u(t - 6)
Answer : Option D
Explaination / Solution:

 and h(t) = u(t)
Taking Laplace Transform we get


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Q.10
The circuit shown below is driven by a sinusoidal input Vi = Vpcos(t/RC). The steady state output vo


A. (Vp/3)cos(t/RC)
B. (Vp/3)sin(t/RC)
C. (Vp/2)cos(t/RC)
D. (Vp/2)sin(t/RC)
Answer : Option A
Explaination / Solution:

 parallel combination of R and C equivalent impedance is

Transfer function can be written as


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