Unit 3 - Practice Quiz

1 What does the term 'Bipolar' in Bipolar Junction Transistor (BJT) signify?

2 How many PN junctions are present in a standard Bipolar Junction Transistor?

3 Which region of a BJT is the most heavily doped?

4 For a BJT to operate in the active region, what must be the biasing conditions of its junctions?

5 Which physical region of a BJT is designed to be the largest in size?

6 What is the standard relationship between the emitter current (), base current (), and collector current () in a BJT?

7 Which current component is typically the smallest in a normally operating BJT?

8 The ratio of dc collector current () to dc emitter current () is denoted by which symbol?

9 In the Common Emitter (CE) configuration, which terminal is common to both the input and output circuits?

10 Which BJT configuration is widely known as an 'emitter follower'?

11 What is the common-emitter current gain commonly denoted by?

12 Which BJT configuration is most commonly used for voltage and power amplification due to its high voltage and current gains?

13 Which transistor configuration is mainly used for impedance matching due to its high input impedance and low output impedance?

14 For a BJT to operate faithfully as a linear amplifier, in which region must it be biased?

15 What is the phase shift between the input signal and the output signal in a Common Emitter (CE) amplifier?

16 When a BJT acts as a closed switch (ON state), in which region is it primarily operating?

17 When a BJT is used as an open switch (OFF state), in which region is it operating?

18 In the cut-off region, what is the biasing status of the BJT junctions?

19 What is the term for the time required for the collector current to rise from 10% to 90% of its final maximum value during switching?

20 Which switching time parameter describes the time required for the minority carriers in the base to be cleared out before the transistor can turn OFF?

21 In a bipolar junction transistor, why is the emitter region heavily doped while the base is kept thin and lightly doped?

22 An NPN transistor is biased in the active region. How does the Early effect (Base-width modulation) impact the effective base width () when the reverse bias voltage is increased?

23 A BJT has a common-emitter current gain . If the emitter current is , what is the approximate value of the collector current ?

24 In a BJT, the reverse leakage current is . If the transistor has an of $0.98$, what is the common-emitter leakage current ?

25 In the Common Emitter (CE) configuration, the output characteristics show a slight upward slope in the active region instead of being perfectly horizontal. Which phenomenon is responsible for this?

26 Why is the Common Collector (CC) configuration frequently used as a buffer amplifier?

27 Compare the phase relationships between the input and output voltages for the three BJT configurations. Which of the following statements is true?

28 Which BJT amplifier configuration is most suitable if a circuit requires both significant voltage gain and significant current gain simultaneously?

29 For a BJT operating as a linear amplifier, the quiescent (Q) point must be stabilized. If the Q-point moves too close to the saturation region due to a temperature increase, what distortion will occur to a large AC input signal?

30 A simple CE amplifier has a collector resistance and operates at a quiescent collector current of . Assuming thermal voltage , what is the approximate magnitude of the intrinsic voltage gain () if the Early effect is ignored?

31 When a BJT is used as a switch, it is driven between the cut-off and saturation regions. Which biasing conditions correctly describe a BJT in deep saturation?

32 To ensure a BJT turns on quickly and enters deep saturation, the base current provided () is often made much larger than the minimum base current required for saturation (). What is the main disadvantage of this 'overdrive' technique?

33 The total turn-on time () of a transistor switch is defined as the sum of two time intervals. Which are they?

34 During the turn-off transient of a saturated BJT, the collector current remains constant at its maximum value for a short period after the base drive is removed. What causes this delay?

35 What is 'punch-through' (or reach-through) in a BJT?

36 A Common Base (CB) amplifier is often used in high-frequency applications. Which characteristic of the CB configuration primarily makes it suitable for this?

37 Which of the following configurations acts as a current buffer, having a low input impedance, high output impedance, and a current gain approximately equal to 1?

38 How can the storage time () of a BJT switch be minimized in practical switching circuits?

39 In standard BJT manufacturing, NPN transistors are generally preferred over PNP transistors for high-speed switching and high-frequency applications. What is the fundamental physical reason for this?

40 The emitter injection efficiency () is a critical parameter for a BJT. How is defined in an NPN transistor?

41 In an NPN BJT operating in the active region, increasing the collector-base reverse bias while keeping constant causes the Early effect. How does this specifically affect the recombination base current and the emitter injection current ?

42 Consider a BJT operating at high collector voltages where avalanche multiplication occurs in the collector-base junction, denoted by a multiplication factor . What is the modified expression for the collector-to-emitter leakage current in terms of the common-base current gain and the collector-base reverse saturation current ?

43 Using the exact h-parameter conversion formulas, which of the following expressions correctly relates the common-emitter input impedance to the common-base h-parameters?

44 In the charge-control model of a BJT, the storage time during the turn-off transient is determined by the time required to remove excess base charge. If a transistor is driven into saturation with a base current and turned off using a reverse base current , what is the mathematical expression for ?

45 Punch-through (or reach-through) in a BJT occurs when the collector-base depletion region extends completely through the base to the emitter-base junction. Which of the following physical configurations significantly lowers the punch-through voltage ?

46 A designer needs to cascade two amplifier stages to connect a very high-impedance source to a very low-impedance load while achieving the maximum possible overall power gain without signal phase inversion. Which combination of configurations is most appropriate?

47 An NPN transistor is utilized as a switch. If the transistor is driven into deep saturation, the forced beta () is defined as . How does relate to the natural active-region current gain , and what is the impact on the turn-off storage time ?

48 In the small-signal hybrid- model of a BJT at high frequencies, the Miller effect significantly impacts the input capacitance. If the amplifier has an unloaded midband voltage gain , the effective input capacitance is approximately:

49 According to the Ebers-Moll equations for a BJT, the emitter current and collector current are defined in terms of the forward and reverse transport factors (, ) and the saturation currents (, ). Which fundamentally required reciprocity relationship must hold for the Ebers-Moll model to be physically valid?

50 The base transport factor of a BJT is limited by carrier recombination in the base, while the emitter injection efficiency is limited by reverse injection from the base into the emitter. If a BJT is designed with a very short base width () but with an equal doping concentration in both the emitter and the base (), what is the expected limiting value of the common-base current gain ?

51 In the Common Base (CB) configuration, the output characteristics ( vs ) show a slight upward slope in the active region. Which h-parameter strictly models this non-ideal slope, and what physical phenomenon causes it?

52 A BJT CE amplifier is biased with a fixed collector current at room temperature (). If the temperature increases to while the biasing circuit perfectly maintains at , what happens to the small-signal transconductance ?

53 When a BJT operates in the reverse active mode (emitter and collector roles swapped), it generally exhibits a very low current gain () and a low breakdown voltage. What is the fundamental physical reason for the low breakdown voltage in this mode?

54 For a given source resistance and load resistance , it is observed that a Common Emitter (CE) amplifier provides both voltage and current gain. If the same transistor is reconfigured into a Common Collector (CC) amplifier, how does the voltage gain mathematically approach its theoretical upper limit?

55 During the turn-on transient of a BJT switch, the delay time is the time elapsed before the collector current reaches 10% of its maximum saturation value. Which of the following physical processes is the PRIMARY contributor to ?

56 In a basic CE amplifier circuit with a collector resistor and Early voltage , the intrinsic voltage gain (assuming an ideal infinite load and source) is limited by the transistor's output resistance . What is the theoretical maximum intrinsic voltage gain ?

57 For a BJT in the Common Emitter (CE) configuration, the short-circuit forward current gain exhibits a strong frequency dependence. If the transition frequency is and the low-frequency gain is , at what frequency does the magnitude of drop by 3 dB, and what is the exact relationship between and ?

58 A given BJT has a common-base current gain that is highly sensitive to temperature. If increases from $0.990$ to $0.995$ due to internal heating, what is the corresponding percentage change in the common-emitter current gain ?

59 To prevent thermal runaway in a BJT power amplifier, a stability factor is defined as . For a standard voltage-divider bias circuit with emitter degradation (resistors , , , and ), what is the exact expression for , and how is stability optimized?

60 In the derivation of minority carrier distributions in a PNP transistor's base region, the base transport factor deviates from unity due to bulk recombination. If the base width is and the minority carrier diffusion length in the base is , the fraction of injected holes surviving recombination is approximated by evaluating the hyperbolic cosine solution of the continuity equation. What is the standard approximation for when ?