This set of Microelectronics Multiple Choice Questions & Answers (MCQs) focuses on “I/V Characteristics a Diode”.
1. Which assumptions regarding the electron and hole current are considered while formulating the ideal characteristics of a diode?
a) The electron and hole current are discontinuous at the junction in the space charge region
b) The electron current is discontinuous at the junction
c) The hole current is discontinuous at the junction
d) The electron and hole current are continuous at the junction in the space charge region
View Answer
Explanation: The electron and hole current are continuous at the junction in the space charge region. This allows us to add the two currents and obtain the total current due to the contribution of electrons and holes.
2. Select the appropriate attribute for the I/V characteristics of a PN junction diode.
a) Unilateral
b) Linear
c) Even
d) Odd
View Answer
Explanation: The ideal I/V characteristics of a PN junction diode is non-linear and unilateral. It is unilateral because it doesn’t show the same response if the polarity and direction of current is reversed. It is non-linear because it shows and exponential relationship between the current and the voltage.
3. How would the I/V characteristics of the diode change if the bulk resistance reduces from 2 Ohms to 1 Ohm?
a) It is parallel to y axis
b) It shifted further from the origin
c) It is bent towards the y axis
d) It is bent towards the x axis
View Answer
Explanation: If the bulk resistance decreases, the total resistance offered by the diode decreases. The slope of the I/V curve gives the conductance, which in this case increases, and it would bend towards the y axis to signify more slope and less resistance.
4. Which of the following properties are present in the I/V characteristics of a diode?
a) Shifts right with increase in temperature
b) Shifts left with increase in temperature
c) Shifts left with decrease in temperature
d) Independent of temperature
View Answer
Explanation: The I/V characteristics show the effect of increasing temperature in a PN Junction. If we increasing the temperature, the space charge width decreases and the threshold voltage decreases. This shifts the I/V characteristics leftwards.
5. If the ideal I/V characteristics is a line parallel to y-axis, what does it neglect?
a) Bulk resistance
b) Static resistance
c) Dynamic resistance
d) Threshold resistance
View Answer
Explanation: The bulk resistance is a sum of the p and the n regions which behave as Ohmic regions. This leads to the I/V characteristics being perpendicular to the V axis at Vth. None of the other resistances are neglected as they are fundamental attributes of the diode.
6. Ignoring the Zener resistance, what will be the impact of the Zener diode on the circuit?
a) Resistance decreases in reverse bias
b) Resistance increases in reverse bias
c) Ideal voltage regulator
d) Draws maximum current for minimum voltage
View Answer
Explanation: An ideal voltage regulator gives a constant voltage independent of the current through it. The Zenner Diode behaves as an ideal voltage regulator in the breakdown region. It’s resistance decreases to allow current but it maintains the voltage until it gets destroyed due to very high currents.
7. What happens to the I/V characteristics of a Zenner Diode when temperature increases?
a) VBR shifts towards origin
b) VBR shifts away from origin
c) VBR shifts towards origin for large temperature change
d) VBR shifts away from origin for large temperature change
View Answer
Explanation: The breakdown voltage decreases with an increase in temperature. By the increase is usually in the order of mV per degree and hence we find that Zener diodes offer operation over a wide range of temperature.
8. What happens to the Zener diode in absence of a current limiting resistor?
a) It can get destroyed
b) Its voltage shifts largely
c) Nothing would happen
d) Diode won’t turn on
View Answer
Explanation: The Zener diode allows a maximum current before getting completely destroyed. The current flowing into it is checked up by a current limiting resistor. This prevents the Zener diode from any harm.
9. We have brought a certain change in a voltage regulator circuit which made the Zener diode off. Which of the following is the change?
a) Heavy loading
b) Low series resistance
c) High input voltage
d) Low loading
View Answer
Explanation: In cases of heavy loading, the load current increases significantly. This leads to very less Zener current which can make the diode turn off. A high series resistance or a low input voltage can also turn the diode off.
10. Which phenomenon allows us to approximate the majority carrier concentration with the doping concentration?
a) Complete Ionization
b) Complete recombination
c) Reduction in threshold voltage
d) Reduction in temperature
View Answer
Explanation: Complete ionization implies all the donor atoms have contributed a charge carrier in the semiconductor region. This amount is so big than the thermal equilibrium majority charge concentration that we can approximate the total number of charge carriers to be equal to the donor concentration.
11. How does the I/V characteristics get affected for the resistance offered by the p and n region?
a) More voltage for same current
b) More current for same voltage
c) Threshold voltage increases
d) Threshold voltage decreases.
View Answer
Explanation: The threshold voltage isn’t affected by the series resistance. The diode would require more voltage, than it would have, while drawing the same current in absence of the series resistance. It is usually negligible but does become significant in certain diodes.
12. The incremental conductance as obtained from the I/V characteristics is denoted as g. Which of the following would be g?
a) ID/VTH
b) IDQ/V
d) IDQ/VT
View Answer
Explanation: The incremental conductance is observed from the I/V curve of the diode. It is the slope of the curve at the quintessential point or q-point. ‘g’ is equal to IDQ/VT where IDQ is the diode current at q-point and can be obtained from the diode equation.
13. What happens to the diffusion resistance with an increase in temperature?
a) Increases linearly
b) Increases non-linearly
c) Increases parabolically
d) Doesn’t get affected
View Answer
Explanation: The diffusion resistance increases with an increase in temperature. It increases non-linearly with temperature and the relation is obtained from the fact that r=VT/IDQ. IDQ is exponentially dependent on temperature while VT is linearly dependent on temperature.
14. The forward bias current is more sensitive to temperature than the reverse biased current.
a) True
b) False
View Answer
Explanation: The forward biased current is exponentially dependent on temperature while the reverse bias current increases 4 times for every 10°C rise in temperature.
15. The electric field inside the diode is 0 as we go away from the junction.
a) True
b) False
View Answer
Explanation: When we are very far away from the depletion space charge width, we encounter a high density of majority charge carriers in the semiconductor region. This electric field is much less in magnitude than the electric field at the junction but it is non-zero due to the drift of majority carriers.
Sanfoundry Global Education & Learning Series – Microelectronics.
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