Electronic Devices and Circuits MCQ

Silicon is mostly used to construct electronic circuits because silicon has a much higher PIV (Peak Inverse Voltage) than the other semiconductors. It is also very cheap.

Zener diode is a heavily doped diode. It is used in reverse bias. It has Zener breakdown. It is used in voltage regulators because it passes an excess amount of current in breakdown mode by maintaining constant voltage across the load.

Solar cell is a photovoltaic cell. No external voltage is applied and solar cell responsivity is directly proportional to the wavelength of the incident light. It doesn’t produce dark current.

LEDs need compound type semiconductors because they have direct band gap. In direct band gap, photons are easily generated when electrons release energy during recombination.

 Degenerative N-type and degenerative p-type semiconductors are used in tunnel diodes. Tunnel diodes are used in microwave electronic devices and circuits.

Mass action law is related to the concentration of electrons and holes in a semiconductor. Degenerative type semiconductors show similar behavior to metal. So, Mass action law is not valid for them.

With a very high amount of doping in degenerative type semiconductors, atoms come closer. For this reason, the interatomic interaction cannot be neglected. So, the effective band gap becomes narrow.

At T = 0K, conductivity will be zero because donar level ionization is zero, so no free electron is there in the conduction band. Conductivity is measured when free electrons are present in the conduction band for conduction

Recombination rate decreases when temperature increases because the electrons that are going to combine with holes in the valence bond are re-excited.

Electronic devices like MOSFET have the lowest turn-off times (nanoseconds). BJT has turn-off times in between nanoseconds to microseconds. IGBT and SCR have turn-off times of about 1 and 5 microseconds respectively.

 Electron-hole pairs can be generated by increasing temperature or ionization or photo excitation. Impurity injection is done for doping of semiconductors. This process doesn’t generate electron-hole pairs.

Due to tunneling, a large number of electrons penetrate through the junction, so a large amount of current is produced. And as we are considering a special diode, we can control its I-V characteristics to improve the switching speed.

Band pass filter depends upon the value of the resistance and capacitance. In varactor diode, we can obtain capacitance by varying the input voltage. As capacitance becomes adjustable, it can be considered as an adjustable band pass filter.

In the saturation region, the emitter-base junction is forward biased, the collector-base junction is also forward biased. This is the operating mode when no current flows through BJT.

When the depletion layer starts moving into the channel, due to the reverse bias of drain and substrate voltage, the inverted charge in the channel decreases from source to drain.

MOSFET is preferred in digital and analog electronic circuits because it is faster than all other transistors. Also, it has a very high input impedance.