# EC GATE 2007 (Test 1)

Tag: ec gate 2007
Q.1
X = and Y = are two 5-bit binary numbers represented in two’s complement format. The sum of X and Y represented in two’s complement format using 6 bits is
A. 100111
B. 0010000
C. 000111
D. 101001
Explaination / Solution:

MSB of Y is 1, thus it is negative number and X is positive number In signed two’s complements from 7 is Workspace
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Q.2
The following binary values were applied to the X and Y inputs of NAND latch shown in the figure in the sequence indicated below :
X =    ,Y =    X =    ,Y =    X =    Y =
The corresponding stable P Q, output will be A. P = ,Q = P = ,Q = P = ,Q = or P = ,Q =
B. P = ,Q = P = ,Q = or P = ,Q = P = ,Q =
C. P = ,Q = P = ,Q = P = ,Q = or P = ,Q =
D. P = ,Q = P = ,Q = P = ,Q =
Explaination / Solution:
No Explaination.

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Q.3
In the Digital-to-Analog converter circuit shown in the figure below, VR = 1V and R = 1kΩ The current i is
A. 31.25μA
B. 62.5μA
C. 125μA
D. 250μA
Explaination / Solution:  Workspace
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Q.4
Consider the Op-Amp circuit shown in the figure. If then the minimum and maximum values of ϕ (in radians) are respectively
A. -(π/2) and π/2
B. 0 and π/2
C. -π and 0
D. -(π/2) and 0
Explaination / Solution: Workspace
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Q.5
Group I lists four different semiconductor devices. match each device in Group I with its charactecteristic property in Group II
Group-I                                      Group-II
(P) BJT                                       (1) Population iniversion
(Q) MOS capacitor                     (2) Pinch-off voltage
(R) LASER diode                        (3) Early effect
(S) JFET                                     (4) Flat-band voltage
A. P - 3, Q - 1, R - 4, S - 2
B. P - 1, Q - 4, R - 3, S - 2
C. P - 3, Q - 4, R - 1, S - 2
D. P - 3, Q - 2, R - 1, S - 4
Explaination / Solution:

In BJT as the B-C reverse bias voltage increases, the B-C space charge region width increases which xB (i.e. neutral base width) > A change in neutral base width will change the collector current. A reduction in base width will causes the gradient in minority carrier concentration to increase, which in turn causes an increased in the diffusion current. This effect si known as base modulation as early effect.
In JFET the gate to source voltage that must be applied to achieve pinch off voltage is described as pinch off voltage and is also called as turn voltage or threshold voltage.
In LASER population inversion occurs on the condition when concentration of electrons in one energy state is greater than that in lower energy state, i.e. a non equilibrium condition.
In MOS capacitor, flat band voltage is the gate voltage that must be applied to create flat ban condition in which there is no space charge region in semiconductor under oxide.
Therefore
BJT : Early effect
MOS capacitor : Flat-band voltage
LASER diode : Population inversion
JFET : Pinch-off voltage

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Q.6
The figure shows the high-frequency capacitance - voltage characteristics of Metal/Sio2/silicon (MOS) capacitor having an area of 1 × 10-4 cm2. Assume that the permittivities (ε0εr) of silicon and Sio are 1 × 10-12 F/cm and 3.5 × 10-13 F/ cm respectively. Consider the following statements about the C − V characteristics plot :
S1 : The MOS capacitor has as n-type substrate
S2 : If positive charges are introduced in the oxide, the C − V polt will shift to the left.
Then which of the following is true?

A. Both S1 and S2 are true
B. S1 is true and S2 is false
C. S1 is false and S2 is true
D. Both S1 and S2 are false
Explaination / Solution:

Depletion region will not be formed if the MOS capacitor has n type substrate but from C-V characteristics, C reduces if V is increased. Thus depletion region must be formed. Hence S1 is false If positive charges is introduced in the oxide layer, then to equalize the effect the applied voltage V must be reduced. Thus the C − V plot moves to the left. Hence S2 is true.

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Q.7
The raised cosine pulse p(t) is used for zero ISI in digital communications. The expression for p(t) with unity roll-off factor is given by The value of p(t) at t = 1/W is
A. −0.5
B. 0
C. 0.5
D.
Explaination / Solution: Workspace
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Q.8
An air-filled rectangular waveguide has inner dimensions of 3 cm × 2 cm. The wave impedance of the TEmode of propagation in the waveguide at a frequency of 30 GHz is (free space impedance η0 = 377Ω)
A. 308 Ω
B. 355 Ω
C. 400 Ω
D. 461 Ω
Explaination / Solution: Workspace
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Q.9
A right circularly polarized (RCP) plane wave is incident at an angle 600 to the normal, on an air-dielectric interface. If the reflected wave is linearly polarized, the relative dielectric constant ξr is. A. √2
B. √3
C. 2
D. 3
Explaination / Solution:
No Explaination.

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Q.10
The correct full wave rectifier circuit is
A. B. C. D.  