GATE EC Electronic Devices questions

Consider an $n$-channel MOSFET having width $W$, length $L$, electron mobility in the channel $\mu _{n}$ and oxide capacitance per unit area $C_{ox}$. If gate-to-source $V_{GS}=0.7$ V, drain-to-source voltage $V_{DS}=0.1 V$, $\mu _{n}C_{ox}=100 \mu A/V^{2}$, threshold voltage $V_{TH}=0.3V$ and $(W/L)=50$, then the transconductance …

In the figure, $D1$ is a real silicon $pn$ junction diode with a drop of $0.7V$ under forward bias condition and $D2$ is a Zener diode breakdown voltage of $-6.8V$. The input $V_{in}(t)$ is a periodic square wave of period $T$, whose one period is shown in the figure. Assuming $10 \tau < < T$, where $\tau$ is the time constant of the …

The switch in the circuit, shown in the figure, was open for a long time and is closed at $t=0$. The current $i(t)$ (in ampere) at $t=0.5$ seconds is ____________

A MOS capacitor is fabricated on $p$-type Si (Silicon) where the metal work function is $4.1$ eV and electron affinity of Si is $4.0$ eV. $E_C-E_F=0.9$ eV, where $E_C$ and $E_F$ are the conduction band minimum and the Fermi energy levels of Si, respectively. Oxide $\epsilon _r=3.9$, $\epsilon _o=8.85\times 10^{-14}$ F/cm, oxide thickness …

An abrupt $pn$ junction (located at $x=0$) is uniformly doped on both $p$ and $n$ sides. The width of the depletion region is $W$ and the electric field variation in the $x$-direction is $E(x)$. Which of the following figures represents the electric field profile near the $pn$ junction?

An electron $(q_1)$ is moving in free space with velocity $10^5$ m/s towards a stationary electron $(q_2)$ far away. The closest distance that this moving electron gets to the stationary electron before the repulsive force diverts its path is ____________$\times 10^{-8}$ m. [Given, mass of electron $m=9.11\times 10^{-31}$ kg, charge of electron …

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

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 $n$-side. No external voltage is applied to the diode. Given: $kT/q = 26 \: mV$, $n_i = 1.5 \times 10^{10} cm^{-3}$ , $\epsilon_{Si} = 12 \varepsilon_0$, …

Consider an $n$-channel metal oxide semiconductor field effect transistor (MOSFET) with a gate-to-source voltage of $1.8$ V. Assume that $\frac{W}{L}=4$, $\mu_NC_{ox}= 70 \times 10^{-6} AV^{-2}$, the threshold voltage is $0.3$V, and the channel length modulation parameter is $0.09 \: V^{-1}$. In the saturation region, the drain conductance (in …

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 _________

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 off at $t=0$. Assume low-level injection to be valid and ignore surface effects. …

A $p-i-n$ photodiode of responsivity $0.8 \: A/W$ is connected to the inverting input of an ideal opamp as shown in the figure, $+V_{CC}= 15 V, \: – V_{CC} = – 15 V$, Load resistor $R_L=10k\Omega$. If $10 \mu W$ of power is incident on the photodiode, then the value of the photocurrent(in $\mu A$) through the load is _________

Identify the circuit below.

The current density in a medium is given by $${\overrightarrow J= \frac{400 \sin\theta}{2\pi(r^2+4)} \hat {a}_r \: Am^{-2}}$$ The total current and the average current density flowing through the portion of a spherical surface $r = 0.8 \: m$, $\frac{\pi}{12} \leq \theta \leq \frac{\pi}{4}$, $0 \leq \phi \leq 2\pi$ are given, respectively, by

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 _________

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 voltage $KT/q$ is $26$ $mV$. The value of $R_{2}$ (in $\Omega)$ for …

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 technology, so that its worst case charge and discharge times while driving the same capacitor are similar. The channel …

In the given circuit, each resistor has a value equal to $1\Omega$. What is the equivalent resistance across the terminals $a$ and $b$?

In the circuit shown in the figure, the magnitude of the current (in amperes) through $R_{2}$ is ____

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 inversion carrier density is $4\times10^{11} cm^{-2}.$ What is the value of …