List of top Electronics and Communication Engineering Questions

In an extrinsic semiconductor, the hole concentration is given to be $1.5n_i$ where $n_i$ is the intrinsic carrier concentration of $1 \times 10^{10}$ $\text{cm}^{-3}$. The ratio of electron to hole mobility for equal hole and electron drift current is given as _____________ (rounded off to two decimal places).

The following circuit(s) representing a lumped element equivalent of an infinitesimal section of a transmission line is/are

The electric field of a plane electromagnetic wave is \[ E = \mathbf{a_x}\,C_{1x}\cos(\omega t - \beta z) + \mathbf{a_y}\,C_{1y}\cos(\omega t - \beta z + \theta)\ \text{V/m}. \] Which of the following combination(s) will give rise to a left handed elliptically polarized (LHEP) wave?

The standing wave ratio on a $50\ \Omega$ lossless transmission line terminated in an unknown load impedance is found to be $2.0$. The distance between successive voltage minima is $30\ \text{cm}$ and the first minimum is located at $10\ \text{cm}$ from the load. $Z_L$ can be replaced by an equivalent length $l_m$ and terminating resistance $R_m$ of the same line. The value of $R_m$ and $l_m$, respectively, are _____________

The S-parameters of a two port network is given as \[ [S] = \begin{bmatrix} S_{11} & S_{12} \\[2pt] S_{21} & S_{22} \end{bmatrix} \] with reference to $Z_0$. Two lossless transmission line sections of electrical lengths $\theta_1 = \beta l_1$ and $\theta_2 = \beta l_2$ are added to the input and output ports for measurement purposes, respectively. The S-parameters $[S']$ of the resultant two port network is

Let $x_1(t)$ and $x_2(t)$ be two band-limited signals having bandwidth $B = 4\pi \times 10^{3}$ rad/s each. In the figure below, the Nyquist sampling frequency, in rad/s, required to sample $y(t)$, is _____________

Let $x(t) = 10\cos(10.5Wt)$ be passed through an LTI system having impulse response \[ h(t) = \pi\left(\dfrac{\sin(Wt)}{\pi t}\right)^2 \cos(10Wt). \] The output of the system is _____________

Consider a discrete-time periodic signal with period $N=5$. Let the discrete-time Fourier series (DTFS) representation be \[ x[n] = \sum_{k=0}^{4} a_k e^{j\frac{2\pi kn}{5}}, \] where $a_0 = 1$, $a_1 = 3j$, $a_2 = 2j$, $a_3 = -2j$, and $a_4 = -3j$. The value of the sum \[ \sum_{n=0}^{4} x[n] \sin\left(\frac{4\pi n}{5}\right) \] is _____________

The h-parameters of a two port network are shown below. The condition for the maximum small signal voltage gain $\dfrac{V_{out}}{V_s}$ is _____________

Let a frequency modulated (FM) signal \[ x(t) = A \cos\left(\omega_c t + k_f \int_{-\infty}^{t} m(\lambda) \, d\lambda \right), \] where $m(t)$ is a message signal of bandwidth $W$. It is passed through a non-linear system with output \[ y(t) = 2x(t) + 5(x(t))^2. \] Let $B_T$ denote the FM bandwidth. The minimum value of $\omega_c$ required to recover $x(t)$ from $y(t)$ is _____________

The switch $S_1$ was closed and $S_2$ was open for a long time. At $t=0$, switch $S_1$ is opened and $S_2$ is closed, simultaneously. The value of $i_c(0^+)$, in amperes, is _____________

In the following block diagram, R(s) and D(s) are two inputs. The output Y(s) is expressed as Y(s) = G$_1$(s)R(s) + G$_2$(s)D(s).
G$_1$(s) and G$_2$(s) are given by

A closed loop system is shown in the figure where $k > 0$ and $\alpha > 0$. The steady state error due to a ramp input $(R(s)=\alpha/s^{2})$ is _____________

In the circuit shown below, $D_1$ and $D_2$ are silicon diodes with cut-in voltage of 0.7 V. $V_{IN}$ and $V_{OUT}$ are input and output voltages in volts. The transfer characteristic is _____________

The $\dfrac{V_{OUT}}{V_{IN}}$ of the circuit shown below is _____________

In the circuit shown below, switch S was closed for a long time. If the switch is opened at $t=0$, the maximum magnitude of the voltage $V_R$, in volts, is _____________ (rounded off to the nearest integer).

For the circuit shown below, the propagation delay of each NAND gate is 1 ns. The critical path delay, in ns, is ___________ (rounded off to the nearest integer).

For the two port network shown below, the [Y]-parameters is given as [Y] = (1/100) * [[2 -1], [-1 4/3]] S. The value of load impedance Z_L, in ohms, for maximum power transfer will be _____________ (rounded off to the nearest integer).

In the circuit shown below, the current $i$ flowing through $200\,\Omega$ resistor is ________ mA (rounded off to two decimal places).

In the table shown below, match the signal type with its spectral characteristics.

\[ \begin{array}{|l|l|} \hline \text{Signal type} & \text{Spectral characteristics} \\ \hline (i) \; \text{Continuous, aperiodic} & (a) \; \text{Continuous, aperiodic} \\ \hline (ii) \; \text{Continuous, periodic} & (b) \; \text{Continuous, periodic} \\ \hline (iii) \; \text{Discrete, aperiodic} & (c) \; \text{Discrete, aperiodic} \\ \hline (iv) \; \text{Discrete, periodic} & (d) \; \text{Discrete, periodic} \\ \hline \end{array} \]

The Fourier transform $X(\omega)$ of $x(t)=e^{-t^{2}}$ is \[ X(\omega)=\sqrt{\pi}\,e^{-\tfrac{\omega^{2}}{4}}. \]

Consider a system with input x(t) and output y(t) = x(e^t). The system is

Let $m(t)$ be a strictly band-limited signal with bandwidth $B$ and energy $E$. Assuming $\omega_0=10B$, the energy in the signal $m(t)\cos \omega_0 t$ is

The synchronous sequential circuit shown below works at a clock frequency of 1 GHz. The throughput, in Mbits/s, and the latency, in ns, respectively, are

In the circuit shown below, P and Q are the inputs. The logical function realized by the circuit shown below is