# EC GATE 2007 (Test 4)

Tag: ec gate 2007
Q.1
The circuit diagram of a standard TTL NOT gate is shown in the figure. Vi = 25 V, the modes of operation of the transistors will be

A. Q1 revere active; Q2 normal active; Q saturation; Q4 cut-off
B. Q1 revere active; Q2 saturation; Q saturation; Q4 cut-off
C. Q1 normal active; Q2 cut-off; Q cut-off; Q4 saturation
D. Q1 saturation; Q2 saturation; Q saturation; Q4 normal active
Explaination / Solution:
No Explaination.

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Q.2
An 8085 assembly language program is given below.
Line 1:   MVI A, B5H
2:   MVI B, OEH
3:   XRI 69H
5:   ANI 9BH
6:   CPI 9FH
7:   STA 3010H
8:   HLT
The contents of the accumulator just execution of the ADD instruction in line 4 will be
A. C3H
B. EAH
C. DCH
D. 69H
Explaination / Solution:

Line 1 : MVI A, B5H ; Move B5H to A
2 : MVI B, 0EH ; Move 0EH to B
3 : XRI 69H      ; [A] XOR 69H and store in A
; Contents of A is CDH
4 : ADDB          ; Add the contents of A to contents of B and
; store in A, contents of A is EAH
5 : ANI 9BH      ; [a] AND 9BH, and store in A,
; Contents of A is 8 AH
6 : CPI 9FH      ; Compare 9FH with the contents of A
; Since 8 AH < 9BH, CY = 1
7 : STA 3010 H  ; Store the contents of A to location 3010 H
8 : HLT               ; Stop
Thus the contents of accumulator after execution of ADD instruction is EAH.

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Q.3
In the Op-Amp circuit shown, assume that the diode current follows the equation I = Ise P(V VT). For V= V, V = V, and for V= V, V = V. The relationship between V and V is

A. V = √V0
B. V0 = e V0
C. V0 = Vn
D. V0 - VVn
Explaination / Solution:

Here the inverting terminal is at virtual ground and the current in resistor and diode current is equal i.e.

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Q.4
Group I lists four types of p − n junction diodes. Match each device in Group I with one of the option in Group II to indicate the bias condition of the device in its normal mode of operation. Group - I Group-II (P) Zener Diode (1) Forward bias (Q) Solar cell (2) Reverse bias (R) LASER diode (S) Avalanche Photodiode
A. P - 1, Q - 2, R - 1, S - 2
B. P - 2, Q - 1, R - 1, S - 2
C. P - 2, Q - 2, R - 1, S- -2
D. P - 2, Q - 1, R - 2, S - 2
Explaination / Solution:

Zener diode and Avalanche diode works in the reverse bias and laser diode works in forward bias. In solar cell diode works in forward bias but photo current is in reverse direction. Thus Zener diode : Reverse Bias Solar Cell : Forward Bias Laser Diode : Forward Bias Avalanche Photo diode : Reverse Bias

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Q.5
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.
The gate oxide thickness in the MOS capacitor is
A. 50 nm
B. 143 nm
C. 350 nm
D. 1 μm
Explaination / Solution:

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Q.6
If S(f) is the power spectral density of a real, wide-sense stationary random process, then which of the following is ALWAYS true?
A. S(0)≤S(f)
B. S(f)≥0
C. S(-f) = -S(f)
D.
Explaination / Solution:
No Explaination.

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Q.7
In a GSM system, 8 channels can co-exist in 200 kHz bandwidth using TDMA. A GSM based cellular operator is allocated 5 MHz bandwidth. Assuming a frequency reuse factor of 1/5, i.e. a five-cell repeat pattern, the maximum number of simultaneous channels that can exist in one cell is
A. 200
B. 40
C. 25
D. 5
Explaination / Solution:

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Q.8
The parallel branches of a 2-wire transmission line re terminated in 100Ω and 200Ω resistors as shown in the figure. The characteristic impedance of the line is Z0 = Ω and each section has a length of λ/4. The voltage reflection coefficient Γ at the input is

A. -j-
B. -5/7
C. j-
D. 5/7
Explaination / Solution:

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Q.9
The electron and hole concentrations in an intrinsic semiconductor are ni per cm3 at 300 K. Now, if acceptor impurities are introduced with a concentration of NA per cm3 (where N>> ni , the electron concentration per cm3 at 300 K will be
A. ni
B. ni + NA
C. NA - ni
D. ni/NA
Explaination / Solution:

As per mass action law
np = ni
If acceptor impurities are introduces

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Q.10
The transfer function of a plant is  The second-order approximation of T s using dominant pole concept is
A.
B.
C.
D.