ISRO Scientist or Engineer Electronics 2018

The circuit shown in the fig. below is a:

($$A_1 \& A_2$$ are ideal op-amps)

Determine the change in collector current, $$\triangle I_c$$ due to change in base emitter voltage $$V_{BE}$$ from $$25^\circ C$$ to $$100^\circ C$$ for a Silicon Transistor in Fixed Bias Configuration having $$\beta = 100$$.
$$($$Consider following variation in Silicon transistor parameters with temperature - At $$T = 25^\circ C, V_{BE} = 0.65 V$$ and At $$T = 100^\circ C. V_{BE} = 0.5 V)$$

An antenna is fed with $$200 \pi W$$ power. The efficiency of the antenna is 75%. If the radiation pattern of the antenna is
$$P(\theta, \phi) = \sin^2 \theta \times \sin^2 \phi$$ for $$0 \leq \phi \leq \pi$$ (elevation angle).
= 0 elsewhere
Find the radiation intensity in the direction of maximum radiation

A reflex klystron is oscillating at 10GHz when operated in $$2\frac{3}{4}$$ mode. find the transit time of the electron in repeller space in nano seconds (ns).

Identify A and B current limiting techniques in a.c. to d.c. power supplies respectively, in the graph below.

A Gold cavity resonator resonating at 10 GHz is fully coated using $$2 \mu m$$ YBCO (Yttrium Barium Copper Oxide) material and operating at boiling temperature of liquid nitrogen.
What is the Skin Depth of RF at this frequency?
Assume $$\sigma_{A \mu} = 4e 7$$ Siemens/meter at cavity operating temperature.

A steady state is achieved in following Network at t = 0, find the time when $$V_{c(t)}$$ will be maximum

Y-parameter for following network is given as

A satellite transmits signals at a frequency of 6 GHz to a user 40000 km away. The free space pathloss incurredby the signal is nearly :

The satellite communication link between two point is established with uplink carrier-tonoise ratio of 20 dB and downlinkcarrier to noise ratio of 14 dB. The overall C/N is close to:

A system generates data at a rate of 5 Mbps. In order to provide resistance to bit errors, a rate $$\frac{1}{2}$$ error correcting code is applied. Further, the data is mapped to a 16-QAM constellation. Whatis the resulting symbol rate?

Consider a binary linear code with parity check matrix H given below.
$$H = \begin{bmatrix}0 & 1 & 1 & 1 & 0 & 0 \\1 & 0 & 1 & 0 & 1 & 0 \\1 & 1 & 0 & 0 & 0 & 1 \end{bmatrix}$$
Which of the following is a valid codeword?

The minimum distance of a (n,k) = (7,4) linear block code is upper bounded by:

Consider a 4-PSK constellation with points $$\left\{\sqrt{2}, j\sqrt{2}, -\sqrt{2}, -j\sqrt{2}\right\}$$ and a 4-PAM constellation {-3, -1, 1, 3}. If all the points in the constellation occur with equal probability, the ratio of average energy of 4-PAM signal to that of 4-PSK signal is:

Difference in number of complex multiplier required for 16 point DFT and 16-point radix-2 FFT is

No of stages(S) in direct form FIR filter is given as
S = integer (K * Fs/ $$\triangle$$ f)
Where Fs = Sampling Frequency, $$\triangle$$f = Filter transition band, K = 3(assume)
If x(n) is signal with frequency range 0-2.4 MHz and sampled at $$F_s = 400$$ MHz and it is filtered by

Assumptions:
Passband Frequency LPF(1): 1.8 MHz, Stop band Frequency LPF(1) : 4 MHz
Passband Frequency LPF(2): 1.8 MHz ,Stopband Frequency LPF(2) : 2 MHz
Both filters are having flat passbands and stopbands
Passband attenuation of both filters = 0 dB and stop bandattenuation of both filters is infinity.
Calculate total no. of stages $$S_{LPF1} + S_{LPF2}$$

Difference in dynamic range of 32-bit binary number(B) and floating point number(F) is?
Standard Format for B and F as given below :

If Sys clock frequency is > 4 * clk_ext frequency. What is the functionality of above circuit?

Simplify the Boolean expression:
$$F(w, x, y, z) = \sum(0, 1, 2, 4, 5, 6, 8, 9, 12, 13, 14)$$

High State noise margin of standard TTL and 5V CMOSlogic gate are

Determine the Voltage transfer characteristics of the following circuit comprising of Zener diodes having identical characteristics with Zener Breakdown voltage $$V_z$$ and Diode cut-in voltage $$V_T$$

Two resistances of values 2Ω and 4Ω made of different materials with temperature coefficients of resistance 3 ppm/$$^\circ C$$ and 6 ppm/$$^\circ C$$ respectively are connected in series. What is the temperature coefficient of resistance of the net resistance?

Which of the following semiconductor compound is not used in the construction of Light Emitting Diodes?

An LCtank circuit resonates at a frequency ‘$$f_r$$’. If the temperature coefficient of permittivity of the dielectric material used in the Capacitance is 6 ppm/$$^\circ C$$, then what is the temperature coefficient of frequency‘$$f_r$$’.

To avoid difficulties with strapping at high frequencies, the type of cavity structure used in the magnetron is,

The transmittime in the repeller space of a reflex klystron must be $$\left(n + \frac{3}{4}\right)$$ cycles to ensure that,

‘For a circuit givenin figure, switch Kis closed to position 1 at t = 0. After t = 1 TC (Time Constant), switch is moved to position 2. Find The Current I at 1TC(-) (just before one-time constant time) and 1TC(+) Gust after one-time constant time) respectively (assume $$\frac{1}{e} \cong 0.37$$)

For a network shown in figure, which of the following statement is true.

Pair of differrential equations that describes motion of planet about sun using first two laws of Kepler is given as:

Two communication antennas A and B, one operating at 300 MHz and other at 3 GHz respectively and having same gain, are illuminated with identical flux density of -100 dBW/m$$^2$$. What is the relation between the received powers $$(P_A : P_B)$$?

Consider identical four, 3-faced dice. When the dice are rolled, the faces of the dice appear with probabilities given below. Which distribution has the maximum entropy?

If System 1 and 2 are Linear Time Invariant systems and same input x(n) is provided both configuration
Statement 1: $$y_1(n) = y_2(n)$$
Statement 2: $$f(n) = g(n)$$

Benefit(s) of Bandpass sampling over low pass sampling

For a signal with $$F_c$$ (Centre Frequency) = 1200 MHz and BW = 100 MHz which of the following Sampling frequency($$F_s$$) will cause spectrum inversion:

If $$x_{in}(t) = \sin(2 * \pi * 4000 * t) + 0.75 * \sin \left(2 * \pi * 5000 * t + \frac{\pi}{4}\right)$$ is sampled with $$F_s = 16000 Hz$$ calculate $$X(0)$$ if $$X(m) = \sum_{n = 0}^{N - 1} x(n) e^{-j2 \pi nm/N}$$ When $$N = 8$$, where $$x(n) = x_{in}(nt_s)$$

VHDL
entity test is
port
(
data : in sd_logic;
clk : in std_logic;
reset : in std_logic;
q : out std_logic
);
end test;
architecture behav of test is
begin
process(clk)
begin
if (clk'event and clk = '1') then
if (reset = '0') then
q $$\leq$$ '0';
else
q $$\leq$$ data;
end if;
end if;
end process;
end behav;
VERILOG
module test (data, clk, reset, q);
input data, clk, reset;
output q;
reg q;
always @ (posedge clk)
if (~reset)
q = 1'b0;
else q = data;
endmodule
The Above Verilog/ VHDL module depicts which sequential element:

An ideal p-n junction diode in series with a 100 Ω resistance is forward biased such that the forward current flowing through the diode is 100 mA. If voltage across this circuit is instantaneously reversed to 20 V at time instant $$t = t_o$$, then the reverse current flowing through the diode at time instant $$t = t_o$$ is approximately given by

Determine output voltage ‘$$V_o$$’ for below circuit where $$V_{in} = \sin (100 \pi t)$$

Determine the channel half-width for an n-channel silicon FET having Gate-to-Source voltage, $$V_{GS} = \frac{V_p}{4}$$, where $$V_p$$ is the Pinch-off voltage and drain current, $$I_d = 0$$. (Consider (a) Donor Concentration $$N_D = 10^{15}$$ electrons/cm$$^3$$ (b) Channel half-width for $$V_{GS} = 0 V$$ is 3 $$\mu$$m).

Design a single section, quarter wave impedance transformer at 6 GHz from 4.75 cm $$\times$$ 2 cm guide to 3.75 cm $$\times$$ 1 em guide. Assume air filled wave guide with transformersection having same width as that of the input and output sections,

A four port directional coupler has 4 : 1 power splitting ratio and has dissipation loss of 3dB. The coupler directivity is 40dB. What fraction of input power P1 will go to ports P2 and P3?

A cell phone transmits at a powerlevel of 800 mW with an antenna gain of 3.0 dB. The cell tower has an antenna gain of 10.0 dB and is at a distance of 5 km away. Transmission frequency is 600 MHz. Noise level at Receiver Input is -95 dBm and required Signal to Noise ratio to close the link is 5 dB. Find the link margin in dB. (assume $$\pi^2 = 10$$)

What is the value of magnetic flux in Weber, if it is 2000 in Maxwell?

How resistance of Eureka varies with temperature?

A resistor R1 = 4 kΩ is connected across the secondary of transformer for which L1 = 0.2H, L2 = 10H and flux coupling coefficient k = 0.5. Find the peak voltage across resistor R1 when 250 V peak voltage at 400 rad/sec is applied to primary winding of transformer.

For a network shown in figure, Calculate current i2.

For a network shown in figure, a steady state is reached with switch k is open. Switch is closed at time t = 0. Calculate $$\left(\frac{di_1}{dt}\right)$$ and $$\left(\frac{di_2}{dt}\right)$$ at t = 0+

Signal flow diagram of following analog computer circuit is

Find the variance of the distribution shown in the figure.

Fourier transform of $$te^{-at} u(t)$$, (where a > 0, u(t) is the Unit step function) is :

Consider waveforms $$\cos(2 \pi f_1 t + \theta)$$ and $$\cos(2 \pi f_2 t), (f_1 > f_2)$$, to be used for non-coherent binary FSK signalling. If the symbol duration is T seconds, and $$\theta$$ is constant arbitrary angle from 0 to $$2 \pi$$, what is the minimum separation required between $$f_1$$ and $$f_2$$ for non-coherent, orthogonal FSK?

Let $$X(e^{j \omega}) = \sum_{n = -\infty}^{\infty} x[n] e^{-j \omega n}$$ and $$x[n] = \frac{1}{2 \pi} \int_{-\pi}^{\pi}X(e^{j \omega})e^{j \omega n}d \omega$$. If $$X(e^{j \omega}) = \frac{1}{(1 - 0.2e^{-j \omega})(1 - 0.1e^{-j \omega})}$$, what is x[n] in terms of unit discrete step function u(n)?

What is the content of Accumulator in binary after execution of following 8051 Assembly code :
MOVA, #27H
MOVR1,A
SWAP A
ANLA, # OFH
MOVB, #10
MUL AB
MOVR2, A
MOVA, R1
ANL A, #0FH
ADD A, R2

In a 16-Bit micro-controller if a two-dimensional integer array A[5][7] is stored at base location 0x8000, Whatis the address of A[4][2]?

Contentof variable flag after following ‘C’ code execution:
Unsigned char flag = 0 $$\times$$ 7 C
flag = flag $$\mid 0 \times 80$$;
flag = flag $$\mid (1 << 4)$$;
flag &=~ (1 << 7);
flag ^= (1 << 6);

Process P1, P2 and P3 with execution time of 6 ms, 4 ms and 2 ms respectively enter in ready state together in order P1, P2, P3. Calculate the waiting and cements of Process P1. Assuming no wait time due to I/O and round robin scheduling with time slot of 2 ms.

A. HDL Coding /RTL Design
B. Synthesis
C. Static Timing Analysis
D. Place and Route
E. Programmingfile generation
What is the correct order of FPGA design flow?

Electric Field of 1 V/m is applied to a Boron doped Silicon semiconductor slab having doping density of $$10^6$$ atoms/cm$$^3$$ at 300K temperature. Determine the approximate resistivity of the slab. (Consider intrinsic carrier concentration of Silicon at 300 K = $$1.5 \times 10^{10}$$ /cm$$^3$$ Hole Mobility = 500 cm$$^2$$/Vsat 300 K; Electron Mobility = 1300 cm$$^2$$/Vs at 300 K).

What will be the voltage reading of DC Voltmeter placed across the terminals of the Diode in the circuit below.

having the following periodical input signal‘$$V_i (t)$$’

(Assume cut-in voltage of the Diode = 0 V; Forward resistance of the Diode = 2 Ω)

A monostatic pulsed radar operating at 30GHz has a transmitter with 2KW O/P power and an antenna with 30dB gain. Minimum detectable signal in the receiver is —100 dBm.
Determine the maximum rangeofthe radar, if it is required to detect a target having radar cross section of 10sq.m (consider $$\log_{10} 4 \pi = 1.1$$). Assume EM wave propagate under ideal conditions.

Which of the following statement is not true about delay line cancellers?

An air filled rectangular waveguide with dimensions a = 75 mm, b = 37.5 mm has same guide wavelength at frequencies $$f_1$$ and $$f_2$$ when operated at $$TE_{10}$$ and $$TE_{20}$$ modes respectively. If the frequency $$f_1$$ is $$\sqrt{13}$$ GHz, what is frequency $$f_2$$ in GHz?

A waveguide of dimensions a = 15 mm and b = 7.5 mm is used as a high-pass filter. If the stop band attenuation required at 8 GHz is ~ 109.2 dB, whatis the length of the filter?
(assume conductor losses to be zero, approximate $$\pi = 3.14$$ and 1 Np ~ 8.69 dB) ($$log_{10}e = 0.4343$$)

An RF signal is applied to a 50 Ω lossless transmission line which is terminated in a load with impedance, $$Z_L = j 50$$. The wave length is 8 cm. Find the position of voltage and current maximum respectively nearest to the load measured from load end?

Which of the following Oscillation types this waveform represents when the difference between input frequency and natural frequency is small? Assume the generating system to be a lossless mechanical system.

Identify the correct sequence of stages in charging of a Lead-Acid battery.

A rocket with lift-off mass of m, is launched from groundlevel. During flight, fuel burns at a constant rate for $$\tau$$ seconds and exhaust gasesare ejecting from the bottom of the rocket at $$\beta$$ Kg/sec with speed of c m/s relative to the rocket. Ignoring air resistance and assume acceleration due to gravity, g as constant, which of the following expression represents velocity of rocket v(t).

For a conservative vector field F below, which of the following is the scalar potential?
$$F = (y^2 \cos x + az^3)\overrightarrow{i}+(2y \sin x - 4)\overrightarrow{j}+(3xz^2 + 2)\overrightarrow{k}$$ a is an integer

Acylindrical waveguide with radius of 3.5 cm has waves travelling in $$TM_{12}$$ mode. The value of $$1^{st}$$ zero of $$2^{nd}$$ order Bessel function is 7. Find the cut-off wavelength for this mode.

Consider a mechanical system shown in figure. Masses are free to slide over frictionless horizontal surface. The equation of motion of mass $$m_1$$ is

For a feedback system shown below, If K: = 0 and K, = 5, then steady state error for unit ramp input is 0.2. What will be the new value of K: and Ka if damping ratio is increased to 0.5 without affecting steady state error:

For a negative unity feedback system, Gain is given by
$$G(s) = \frac{0.25}{((s^2 + 1)(8s + 3))}$$
Transfer function of a lead compensator aimed at achieving gain crossover frequency of 0.5 rad/sec and phase margin of 30 deg is

A sensitivity of transfer function $$T = \frac{(A_1 + kA_2)}{(A_3 + kA_4)}$$ with respect to parameter k is given by

If over the course of a day, the maximum electron density in the ionosphere varies from $$10^{11}$$ to $$10^{12}$$ $$m^{-3}$$; the critical frequency changes approximately from:

What is the peak to average power ratio for the signal $$x(t) = A \sin(\omega t)$$ with 50% duty cycle?

A binary communication system receives equally likely symbols $$x_1(t)$$ and $$x_2(t)$$ plus Additive White Gaussian Noise at the input of matched detector. If the noise power spectral density ($$N_o$$) is $$10^{-11}$$ W/Hz, compute $$E_b/N_o$$ (in dB). Assume system characteristics impedance as 1Ω.

x(t) = {
1, $$0 \leq t \leq T$$
0, Otherwise
}
h(t) = {
t, $$0 \leq t \leq 2T$$
0, otherwise
}
Calculate $$y(t) = x(t) * y(t)$$, where * denotes convolution for interval $$T \leq t \leq 2T$$

Which of these is non-operational attribute of embedded system?

For the below mentioned 8051 assembly code
Timeelapse : MOV RO, #100
Part 1 : MOVRI, #50
Part 2 : MOV R2#248
Part 3 : DJNZ R2, Part 3
: DJNZ R1, Part 2
: DJNZ RO, Part 1
Assumptions:
* Microcontroller is running at 12 MHz frequency and 1 machine cycle is having 12 clock cycles
* MOV instruction takes 1 Machine cycle
* DJNZ instruction takes 2 Machine cycle
Calculate time required for execution of Part 1

A. Program Counter(PC) Pushedto Stack
B. Generate LCALLto ISR
C. Complete Execution of instruction in progress
D. Clear the interrupt flag
E. Set interrupt in progress
Correct order of execution of action taken by 8051 micro-controllers when an interrupt occurs: