# EC GATE 2011 (Test 4)

Tag: ec gate 2011
Q.1
Choose the most appropriate word from the options given below to complete the following sentence: Under ethical guidelines recently adopted by the Indian Medical Association, human genes are to be manipulated only to correct diseases for which______________ treatments are unsatisfactory.
A. Similar
B. Most
C. Uncommon
D. Available
Explaination / Solution:

Available is appropriate because manipulation of genes will be done when other treatments are not useful.

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Q.2
When the output Y in the circuit below is ‘1’, it implies that data has A. changed from 0 to 1
B. changed from 1 to 0
C. changed in either direction
D. not changed
Explaination / Solution:
No Explaination.

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Q.3
The first six points of the 8-point DFT of a real valued sequence are 5, 1 - j3, 0, 3 - 4j, 0 and 3 + 4j .....The last two points of the DFT are respectively
A. 0, 1 - j3
B. 0, 1 + j3
C. 1 + j3, 5
D. 1 - j3, 5
Explaination / Solution:

For 8 point DFT, and it is conjugate symmetric about x, x = 0; x = 1 + j3

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Q.4
A silicon PN junction is forward biased with a constant current at room temperature. When the temperature is increased by 10ºC, the forward bias voltage across the PN junction
A. increases by 60 mV
B. decreases by 60 mV
C. increases by 25 mV
D. decreases by 25 mV
Explaination / Solution:

For every 1º C increase in temperature, forward bias voltage across diode decreases by 2.5 mV. Thus for 10º C increase, there us 25 mV decreases

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Q.5
The channel resistance of an N-channel JFET shown in the figure below is 600Ω when the full channel thickness (tch) of 10μm is available for conduction. The built-in voltage of the gate PN junction (Vbi) is -1 V. When the gate to source voltage (VGS) is 0 V, the channel is depleted by 1 μm on each side due to the built in voltage and hence the thickness available for conduction is only 8 μm The channel resistance when VGS = 0 V is
A. 480 Ω
B. 600 Ω
C. 750 Ω
D. 1000 Ω
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Q.6
The Column-I lists the attributes and the Column-II lists the modulation systems. Match the attribute to the modulation system that best meets it Column-I P. Power efficient transmission of signals Q. Most bandwidth efficient transmission of voice signals R. Simplest receiver structure S. Bandwidth efficient transmission of signals with Significant dc component Column-II 1. Conventional AM 2. FM 3. VSB 4. SSB-SC
A. P-4;Q-2;R-1;S-3
B. P-2;Q-4;R-1;S-3
C. P-3;Q-2;R-1;S-4
D. P-2;Q-4;R-3;S-1
Explaination / Solution:

In FM the amplitude is constant and power is efficient transmitted. No variation in power. There is most bandwidth efficient transmission in SSB- SC. because we transmit only one side band. Simple Diode in Non linear region ( Square law ) is used in conventional AM that is simplest receiver structure. In VSB dc. component exists.

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Q.7
A four-phase and an eight-phase signal constellation are shown in the figure below. For the constraint that the minimum distance between pairs of signal points be d for both constellations, the radii r1, and r2 of the circles are
A. r1 = 0.707d, r2 = 2.782d
B. r1 = 0.707d, r2 = 1.932d
C. r1 = 0.707d, r2 = 1.545d
D. r1 = 0.707d, r2 = 1.307d
Explaination / Solution:

Four phase signal constellation is shown below d2 = r12 + r12
d2 = 2r12

r1 = d/√2 = 0.707d  Workspace
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Q.8
The block diagram of a system with one input it and two outputs y1 and y2 is given below A state space model of the above system in terms of the state vector and the output vector is.
A. B. C. D. Explaination / Solution: Drawing SFG as shown below  Workspace
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Q.9
If the unit step response of a network is (1 – e-αt),  then its unit impulse response is
A. αe-αt
B. α-1e-αt
C. (1 - α-1)eαt
D. (1 - α)e-αt
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Q.10
The electric and magnetic fields for a TEM wave of frequency 14 GHz in a homogeneous medium of relative permittivity εr and relative permeability  Assuming the speed of light in free space to be 3 × 108 m/s, the intrinsic impedance of free space to be 120π, the relative permittivity εr of the medium and the electric field amplitude Ep are
A. ε= 3, Ep= 120π
B. ε= 3, Ep= 360π
C. ε= 9, Ep= 360π
D. ε= 9, Ep= 120π
From the expressions of we can write, 