GATE EC 2014 Question Paper (16-Feb-2014) (Shift 2)

An N-type semiconductor having uniform doping is biased as shown in the figure.



If E${}_C$ is the lowest energy level of the conduction band, E${}_V$ is the highest energy level of the valance band and E${}_F$ is the Fermi level, which one of the following represents the energy band diagram for the biased N-type semiconductor?

Consider the common-collector amplifier in the figure (bias circuitry ensures that the transistor operates in forward active region, but has been omitted for simplicity). Let I${}_C$ be the collector current, V${}_{BE}$ be the base-emitter voltage and V${}_T$ by the thermal voltage. Also, 𝑔${}_{\text{m}}$ and 𝑟${}_{\text{o}}$ are the small-signal transconductance and output resistance of the transistor, respectively. Which one of the following conditions ensures a nearly constant small-signal voltage gain for a wide range of values of R${}_E$?

A BJT in a common-base configuration is used to amplify a signal received by a 50 Ω antenna. Assume kT/q = 25 mV. The value of the collector bias current (in mA) required to match the input impedance of the amplifier to the impedance of the antenna is________.

For the common collector amplifier shown in the figure, the BJT has high β, negligible V${}_{CE(sat)}$, and V${}_{BE}$ = 0.7 V. The maximum undistorted peak-to-peak output voltage V₀ (in Volts) is _______.

An $8-\mathrm{to}-1$ multiplexer is used to implement a logical function $\mathrm{Y}$ as shown in the figure. Then the output $\mathrm{Y}$ is given by