Recent questions and answers in Electronic Devices

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GATE ECE 2020 | Question: 7
Consider the recombination process via bulk traps in a forward biased $pn$ homojunction diode. The maximum recombination rate is $U_{\text{max}}$ ... bias. With all other parameters unchanged, $U_{\text{max}}$ increases if the thermal velocity of the carriers increases.

jothee asked in Electronic Devices Feb 13, 2020

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GATE ECE 2020 | Question: 31
A one-sided abrupt $pn$ junction diode has a depletion capacitance $C_{D}$ of $50$ $\text{pF}$ at a reverse bias of $0.2 V$. The plot of $1/C^{2}_{D}$ versus the applied voltage $V$ for this diode is a straight line as shown in the figure below. The slope of the plot is ___________ $\times 10^{20}F^{-2}V^{-1}$. $-5.7$ $-3.8$ $-1.2$ $-0.4$

jothee asked in Electronic Devices Feb 13, 2020

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3

GATE ECE 2020 | Question: 34
A $pn$ junction solar cell of area $1.0\:cm^{2}$, illuminated uniformly with $100\:mW\:cm^{-2}$, has the following parameters: Efficiency $= 15\%$, open circuit voltage $= 0.7\:V$, fill factor $= 0.8$, and thickness $=200 \mu m$ ... $0.84\times 10^{19}.$ $5.57\times 10^{19}.$ $1.04\times 10^{19}.$ $83.60\times 10^{19}.$

jothee asked in Electronic Devices Feb 13, 2020

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GATE ECE 2020 | Question: 36
An enhancement $\text{MOSFET}$ of threshold voltage $3\:V$ is being used in the sample and hold circuit given below. Assume that the substrate of the $\text{MOS}$ device is connected to $-10\:V$. If the input voltage $V_{1}$ lies between $\pm 10\:V,$ the minimum and the maximum ... $\text{10 V and -10 V}$. $\text{13 V and -7 V}$. $\text{10 V and -13 V}$.

jothee asked in Electronic Devices Feb 13, 2020

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GATE ECE 2019 | Question: 8
Which one of the following options describes correctly the equilibrium band diagram at $T=300\:K$ of a Silicon $pnn^{+}\:\:p^{++}$ configuration shown in the figure?

Arjun asked in Electronic Devices Feb 12, 2019

by Arjun

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GATE ECE 2019 | Question: 9
The correct circuit representation of the structure shown in the figure is

Arjun asked in Electronic Devices Feb 12, 2019

by Arjun

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7

GATE ECE 2019 | Question: 10
The figure shows the high-frequency C-V curve of a MOS capacitor $(\text{at}\: T=300\: K)$ with $\Phi_{ms}= 0\: V$ and no oxide charges. The flat-band, inversion, and accumulation conditions are represented, respectively, by the points $P,Q,R$ $Q,R,P$ $R,P,Q$ $Q,P,R$

Arjun asked in Electronic Devices Feb 12, 2019

by Arjun

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8

GATE ECE 2019 | Question: 11
What is the electric flux $\left(\int \vec{E}.d \hat{a}\right)$ through a quarter-cylinder of height $H$ (as shown in the figure) due to an infinitely long line charge along the axis of the cylinder with a charge density of $Q?$ $\frac{HQ}{\varepsilon_{0}}$ $\frac{HQ}{4\varepsilon_{0}}$ $\frac{H\varepsilon_{0}}{4Q}$ $\frac{4H}{Q\varepsilon_{0}}$

Arjun asked in Electronic Devices Feb 12, 2019

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9

GATE ECE 2019 | Question: 13
A standard CMOS inverter is designed with equal rise and fall times $(\beta_{n}=\beta_{p}).$ If the width of the pMOS transistor in the inverter is increased, what would be the effect on the LOW noise margin $NM_{L}$ and the HIGH noise margin $NM_{H}$? ... . $NM_{L}$ decreases and $NM_{H}$ increases. Both $NM_{L}$ and $NM_{H}$ increases. No change in the noise margins.

Arjun asked in Electronic Devices Feb 12, 2019

by Arjun

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10

GATE ECE 2019 | Question: 35
The quantum efficiency $(\eta)$ and responsivity $(R)$ at wavelength $\lambda \:(\text{in}\: \mu m)$ in a p-i-n photodetector are related by $R= \frac{\eta \times \lambda}{1.24}$ $R= \frac{\lambda}{\eta \times 1.24}$ $R= \frac{1.24 \times\lambda}{\eta}$ $R= \frac{1.24}{\eta \times \lambda}$

Arjun asked in Electronic Devices Feb 12, 2019

by Arjun

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GATE ECE 2019 | Question: 36
Two identical copper wires $W1$ and $W2$ placed in parallel as shown in the figure, carry currents $I$ and $2I$, respectively, in opposite directions. If the two wires are separated by a distance of $4r$, then the magnitude of the magnetic field $\overrightarrow{B}$ between the wires at a ... $\frac{5\mu_{0}I}{6\pi r}$ $\frac{\mu_{0}^{2}I^{2}}{2\pi r^{2}}$

Arjun asked in Electronic Devices Feb 12, 2019

by Arjun

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12

GATE ECE 2019 | Question: 38
In the circuit shown, the breakdown voltage and the maximum current of the Zener diode are $20\:V$ and $60\:mA$, respectively. The values of $R_{1}$ and $R_{L}$ are $200\: \Omega$ and $1\:k\Omega,$ respectively. What is the range of $V_{i}$ that will maintain the Zener diode in the on' ... $34\: V$ $24\: V$ to $36\: V$ $18\: V$ to $24\: V$ $20\: V$ to $28\: V$

Arjun asked in Electronic Devices Feb 12, 2019

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GATE ECE 2019 | Question: 41
The $\text{RC}$ circuit shown below has a variable resistance $R(t)$ given by the following expression: $R(t)=R_{0}\left(1-\frac{t}{T}\right) \text{for} \:\: 0 \leq t < T$ where $R_{0}=1\: \Omega,$ and $C=1\:F.$ ... $t=0$ is $1\: A,$ then the current $I(t)$, in amperes, at time $t=T/2$ is __________ (rounded off to $2$ decimal places).

Arjun asked in Electronic Devices Feb 12, 2019

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14

GATE ECE 2019 | Question: 49
In an ideal $pn$ junction with an ideality factor of $1$ at $T=300\:K,$ the magnitude of the reverse-bias voltage required to reach $75\%$ of its reverse saturation current, rounded off to $2$ decimal places, is ______ $mV.$ $[k=1.38 \times 10^{-23} JK^{-1}, h=6.625 \times 10^{-34} J-s, q=1.602 \times 10^{-19}C]$

Arjun asked in Electronic Devices Feb 12, 2019

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15

GATE ECE 2019 | Question: 50
Consider a long-channel MOSFET with a channel length $1\:\mu m$ and width $10\: \mu m.$ The device parameters are acceptor concentration $N_{A}=5 \times 10^{16}\: cm^{-3},$ electron mobility $\mu_{n}=800\: cm^{2}/V-s,$ ... _______ $mA$ (rounded off to two decimal places.). $[\varepsilon_{0}=8.854 \times 10^{-14}F/cm, \varepsilon_{si} =11.9]$

Arjun asked in Electronic Devices Feb 12, 2019

by Arjun

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16

GATE ECE 2019 | Question: 52
In the circuit shown. $V_{s}$ is a $10\:V$ square wave of period, $T=4\: ms$ with $R=500\: \Omega$ and $C= 10\:\mu F.$ The capacitor is initially uncharged at $t=0,$ and the diode is assumed to be ideal. The voltage across the capacitor $(V_{c})$ at $3\:ms$ is equal to _____ volts (rounded off to one decimal place)

Arjun asked in Electronic Devices Feb 12, 2019

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17

GATE ECE 2019 | Question: 53
A CMOS inverter, designed to have a mid-point voltage $V_{1}$ equal to half of $V_{dd}.$ as shown in the figure, has the following parameters: $V_{dd}=3V$ $\mu_{n} C_{ox}=100\: \mu A/V^{2}; V_{tn}=0.7\:V $ for $\text{nMOS}$ ... of $\left(\frac{W}{L}\right)_{n}$ to $\left(\frac{W}{L}\right)_{p}$ is equal to _______ (rounded off to $3$ decimal places).

Arjun asked in Electronic Devices Feb 12, 2019

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18

GATE ECE 2019 | Question: 54
In the circuit shown, the threshold voltages of the $pMOS\:\: (|V_{tp}|)$ and $nMOS\:\: (V_{tn})$ transistors are both equal to $1\:V.$ All the transistors have the same output resistance $r_{ds}$ of $6\:M\Omega.$ The other ... area. Ignoring the effect of channel length modulation and body bias, the gain of the circuit is ______ (rounded off to $1$ decimal place).

Arjun asked in Electronic Devices Feb 12, 2019

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19

GATE ECE 2016 Set 3 | Question: 11
The figure shows the band diagram of a Metal Oxide Semiconductor (MOS). The surface region of this MOS is in inversion accumulation depletion flat band

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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20

GATE ECE 2016 Set 3 | Question: 12
The figure shows the $I-V$ characteristics of a solar cell illuminated uniformly with solar light of power $100\ mW/cm^2$. The solar cell has an area of $3\ cm^2$ and a fill factor of $0.7$. The maximum efficiency (in $\%$) of the device is _______

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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21

GATE ECE 2016 Set 3 | Question: 33
In the figure shown, the current $i$ (in ampere) is _________

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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22

GATE ECE 2016 Set 3 | Question: 38
Figures I and II show two MOS capacitors of unit area. The capacitor in Figure I has insulator materials $X$ (of thickness $t_1 = 1$ nm and dielectric constant $\varepsilon_1=4$) and $Y$ (of thickness $t_2 = 3$ ... of thickness $t_{Eq}$. If the capacitors are of equal capacitance, then the value of $t_{Eq}$ (in nm) is _________

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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23

GATE ECE 2016 Set 3 | Question: 39
The $I-V$ characteristics of the zener diodes $D1\:\text{and}\:D2$ are shown in Figure I. These diodes are used in the circuit given in Figure II. If the supply voltage is varied from $0$ to $100$ V,then breakdown occurs in $D1$ only $D2$ only both $D1$ and $D2$ none of $D1$ and $D2$

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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24

GATE ECE 2016 Set 3 | Question: 40
For the circuit shown in the figure, $R_1=R_2=R_3=1\;\Omega,\;L=1\:\mu H$ and $C=1\:\mu F$. If the input $V_{in}=\cos(10^6t)$, then the overall voltage gain $(V_{out}/V_{in})$ of the circuit is _________

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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25

GATE ECE 2016 Set 2 | Question: 13
Assume that the diode in the figure has $V_{on}=0.7 \:V$, but it otherwise ideal. The magnitude of the current $i_{2}$ in mA) is equal to _________

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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26

GATE ECE 2016 Set 2 | Question: 14
Resistor $R_{1}$ in the circuit below has been adjusted so that $I_{1}=1$ $mA$. The bipolar transistors $Q1$ and $Q2$ are perfectly matched and have very high current gain, so their base currents are negligible. The supply voltage $V_{cc}$ is $6$ $V$. The thermal ... $KT/q$ is $26$ $mV$. The value of $R_{2}$ (in $\Omega)$ for which $I_{2}=100\mu A$ is _________

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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27

GATE ECE 2016 Set 2 | Question: 16
Transistor geometries in a $CMOS$ inverter have been adjusted to meet the requirement for worst case charge and discharge times for driving a load capacitor $C$. This design is to be converted to that of a $NOR$ circuit in the same ... should not be changed. Widths of $PMOS$ transistors should be unchanged, while widths of $NMOS$ transistors should be halved.

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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28

GATE ECE 2016 Set 2 | Question: 30
In the given circuit, each resistor has a value equal to $1\Omega$. What is the equivalent resistance across the terminals $a$ and $b$? $1/6 \: \Omega$ $1/3 \: \Omega$ $9/20 \: \Omega$ $8/15 \: \Omega$

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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29

GATE ECE 2016 Set 2 | Question: 31
In the circuit shown in the figure, the magnitude of the current (in amperes) through $R_{2}$ is ____

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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30

GATE ECE 2016 Set 2 | Question: 35
A voltage $V_{G}$ is applied across a $MOS$ capacitor with metal gate and $p$-type silicon substrate at $T=300$ $K$. The inversion carrier density (in number of carriers per unit area) for $V_{G}= 0.8$ $V$ is $2\times 10^{11} cm^{-2}.$ For $V_{G}= 1.3$ $V$, the ... $6.0\times 10^{11}cm^{-2}$ $7.2\times 10^{11}cm^{-2}$ $8.4\times 10^{11}cm^{-2}$

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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31

GATE ECE 2016 Set 2 | Question: 36
Consider avalanche breakdown in a silicon $p^{+}n$ junction. The $n$-region is uniformly doped with a donor density $N_{D}.$ ... $N_{D}\times {V_{BR}}= \text{constant}$ $N_{D}/{V_{BR}}= \text{constant}$

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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32

GATE ECE 2016 Set 2 | Question: 37
Consider a region of silicon devoid of electrons and holes, with an ionized donor density of $N_{d}^{+}=10^{17} cm^{-3}.$ The electric field at $x = 0$ is $0\: V/cm$ and the electric field at $x=L$ is $50$ $kV/cm$ in the positive $x$ direction, ... $\epsilon _{r}=11.7$ for silicon, the value of $L$ in $nm$ is ___________

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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33

GATE ECE 2016 Set 2 | Question: 39
The figure shows a half-wave rectifier with a $475 \: \mu F$ filter capacitor. The load draws a constant current $I_{o}= 1 \: A$ from the rectifier. The figure also shows the input voltage $V_{i}$, the output voltage $V_{C}$ and the peak-to-peak voltage ... an amplitude of $10 \: V$ and a period of $1 \: ms$. The value of the ripple $u$ (in volts) is _________

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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34

GATE ECE 2016 Set 2 | Question: 40
In the opamp circuit shown, the Zener diodes $Z1$ and $Z2$ clamp the output voltage $V_{0}$ to $+5V$ or $-5 V$. The switch $S$ is initially closed and is opened at time $t=0$. The time $t=t_{1}$ (in seconds) at which $V_{0}$ changes state is ________

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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35

GATE ECE 2016 Set 2 | Question: 52
The parallel-plate capacitor shown in the figure has movable plates. The capacitor is charged so that the energy stored in it is $E$ when the plate separation is $d$. The capacitor is then isolated electrically and the plate are moved such that the plate ... , what is the energy stored in the capacitor, neglecting fringing effects? $2E$ $\sqrt{2}E$ $E$ $E/2$

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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36

GATE ECE 2016 Set 1 | Question: 13
Consider the constant current source shown in the figure below. Let $\beta$ represent the current gain of the transistor. The load current $I_0$ through $R_L$ is $I_0 = \bigg( \frac{\beta+1}{\beta} \bigg) \frac{V_{ref}}{R}$ ... $I_0 = \bigg (\frac{\beta}{\beta+1} \bigg) \frac{V_{ref}}{2R}$

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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37

GATE ECE 2016 Set 1 | Question: 36
Consider a silicon $p-n$ junction with a uniform acceptor doping concentration of $10^{17} cm^{-3}$ on the $p$-side and a uniform donor doping concentration of $10^{16}cm^{-3}$ on the $n$ ... $nC \: cm^{-2}$) in the depletion region on the $p$-side is _________

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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38

GATE ECE 2016 Set 1 | Question: 37
Consider an $n$-channel metal oxide semiconductor field effect transistor (MOSFET) with a gate-to-source voltage of $1.8$ V. Assume that $\frac{W}{L}=4$, $\mu_NC_{ox}= 70 \times 10^{-6} AV^{-2}$ ... channel length modulation parameter is $0.09 \: V^{-1}$. In the saturation region, the drain conductance (in micro siemens) is _________

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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39

GATE ECE 2016 Set 1 | Question: 38
The figure below shows the doping distribution in a $p$-type semiconductor in log scale. The magnitude of the electric field (in $kV/cm$) in the semiconductor due to non uniform doping is _________

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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40

GATE ECE 2016 Set 1 | Question: 39
Consider a silicon sample at $T = 300 \: K$, with a uniform donor density $N_d = 5 \times 10 ^{16} cm^{-3}$ , illuminated uniformly such that the optical generation rate is $G_{opt}=1.5 \times 10^{20} cm^{-3}s^{-1}$ throughout the sample. The incident radiation is turned ... $3.73 \times 10^{11}cm^{-3}$ $7.5 \times 10^{13}cm^{-3}$ and $4.12 \times 10^{11}cm^{-3}$

Milicevic3306 asked in Electronic Devices Mar 28, 2018

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