Analog Electronics MCQ Questions & Answers | ECE

Option A: Current controlled Current source
A current-controlled current source (CCCS) means the output current is proportional to the input current. However, the operation of a JFET does not involve control of current by another current. Therefore, this option is incorrect.

Option B: Current controlled Voltage source
A current-controlled voltage source (CCVS) implies the output voltage is controlled by the input current. Since the JFET is voltage-controlled, its output voltage is not directly dependent on the current. Hence, this option is incorrect.

Option C: Voltage controlled Voltage source
A voltage-controlled voltage source (VCVS) suggests that the output voltage is influenced by the input voltage. Although the JFET is voltage-controlled, its output behavior is better described as controlling current, not voltage. Thus, this option is also incorrect.

Option D: Voltage controlled Current source
A voltage-controlled current source (VCCS) means the output current is controlled by the input voltage. In a JFET, the gate-to-source voltage controls the current flowing through the drain-source channel. This aligns with the operation of the JFET, making this option correct.

Conclusion:
The action of a JFET in its equivalent circuit can best be represented as a Voltage controlled Current source (Option D).

Option A: 99%
An efficiency of 99% is highly unlikely for a Common Base (CB) amplifier. Such a high efficiency is typically not achievable in practical amplifier circuits due to inherent losses in the components and design. Therefore, this option is incorrect.

Option B: 85%
An efficiency of 85% is possible for certain types of amplifiers like Class C amplifiers, which are specifically designed for high efficiency. However, the CB amplifier operates in Class A mode, which inherently limits its maximum efficiency. Hence, this option is incorrect.

Option C: 50%
For a CB amplifier operating in Class A mode, the theoretical maximum efficiency is 50%. This is due to the symmetrical operation of the circuit, where half the power is dissipated as heat in the transistor. Therefore, this option is correct.

Option D: 25%
An efficiency of 25% is too low for a CB amplifier operating in Class A mode. While practical losses can reduce efficiency, it typically does not drop this low under normal operating conditions. Hence, this option is incorrect.

Conclusion:
The maximum efficiency of a CB amplifier could be 50% (Option C).

Option A: The edge of the depletion region on the p-side
At the edge of the depletion region on the p-side, the electric field is not maximum. The field strength gradually reduces as you move away from the junction towards the edges of the depletion region. Therefore, this option is incorrect.

Option B: The edge of the depletion region on the n-side
Similarly, at the edge of the depletion region on the n-side, the electric field is not at its peak. The field strength diminishes as you approach the edges of the depletion region. Thus, this option is incorrect.

Option C: The p⁺n junction
In a p⁺n junction diode under reverse bias, the electric field is maximum at the junction itself. This is because the maximum charge separation occurs at the junction, resulting in the highest electric field strength. Hence, this option is correct.

Option D: The center of the depletion region on the n-side
The center of the depletion region on the n-side does not experience the maximum electric field. As you move away from the junction, the electric field strength decreases, making this option incorrect.

Conclusion:
In a p⁺n junction diode under reverse bias, the magnitude of the electric field is maximum at the p⁺n junction (Option C).

Option A: Resistor between source and load
A resistor between the source and load allows both AC and DC components of the signal to pass. It does not block the DC component, which is not suitable when the goal is to prevent DC return. Therefore, this option is incorrect.

Option B: Inductor between source and load
An inductor primarily opposes changes in current and allows DC to pass through while blocking high-frequency AC signals. Since it does not block DC, it cannot prevent a DC return. Hence, this option is incorrect.

Option C: Capacitor between source and load
A capacitor blocks DC components and allows AC signals to pass through due to its property of impedance, which is inversely proportional to frequency. This makes it the ideal component to prevent DC return between the source and load. Therefore, this option is correct.

Option D: Either A or B
Neither a resistor nor an inductor can effectively prevent DC return as they allow DC to pass through. Thus, this option is incorrect.

Conclusion:
To prevent a DC return between the source and load, it is necessary to use a capacitor (Option C).

A constant current signal across a parallel RLC circuit gives an output of 1.4v at the signal frequencies of 3.89kHz and 4.1kHz. This indicates that the circuit is operating near its resonant frequency.

At resonance, the impedance of the parallel RLC circuit is maximum, leading to a maximum voltage across it for a given current. In this case, the output voltage is 1.4v at frequencies close to resonance.

As we move further away from the resonant frequency, the impedance decreases, and consequently, the output voltage also decreases.

Therefore, at 4kHz, which is closer to the resonant frequency than 3.89kHz or 4.1kHz, the output voltage will be **slightly higher** than 1.4v.

Among the given options, Option B: 2v is the closest to this expected value.

$$\eqalign{ & {I_{\text{C}}} = \frac{{{I_{{\text{CO}}}}}}{{1 - \alpha }} + \frac{\alpha }{{1 - \alpha }} \times {I_\beta } \cr & = \frac{6}{{1 - 0.98}} + \frac{{0.98}}{{1 - 0.98}} \times 100 \cr & = 5.2\,{\text{mA}} \cr} $$

Explanation of each option:

Option A: Junction capacitance is associated with a p-n junction. This capacitance arises due to the separation of charge carriers across the junction, creating an electric field that contributes to capacitance.

Option B: Charge storage capacitance is also associated with a p-n junction. It refers to the capacitance that stores charge at the junction when it is forward biased, as the charge carriers accumulate at the junction.

Option C: Depletion capacitance is related to a p-n junction as well. It occurs due to the depletion region that forms at the junction when it is reverse biased, and this region acts like a capacitor.

Option D: Channel length modulation is not associated with a p-n junction. This phenomenon is related to field-effect transistors (FETs), where the effective length of the channel is modulated by the drain-to-source voltage, and does not occur in p-n junctions.

Conclusion: The correct answer is Option D: Channel length modulation because it is not associated with a p-n junction.

Explanation of each option:

Option A: CC-CB is incorrect because this configuration consists of a common collector (CC) stage followed by a common base (CB) stage. While this can be used in some amplifiers, it is not a typical configuration for a cascade amplifier.

Option B: CE-CB is incorrect because this configuration consists of a common emitter (CE) stage followed by a common base (CB) stage. While this may be used in certain applications, it is not the standard configuration for a cascade amplifier.

Option C: CB-CC is incorrect because this configuration starts with a common base (CB) stage followed by a common collector (CC) stage. This is also not a common arrangement for cascade amplifiers.

Option D: CE-CC is correct because the typical cascade amplifier configuration uses a common emitter (CE) stage followed by a common collector (CC) stage. The CE stage provides high voltage gain, while the CC stage provides current gain and impedance matching, making this a common choice for multistage amplifiers.

Conclusion: The correct answer is Option D: CE-CC because this is the standard multistage configuration for cascade amplifiers.

Option A: Reduces gain is correct because negative feedback in an amplifier reduces the overall gain of the system. This reduction in gain, however, leads to improved linearity, reduced distortion, and better stability in the amplifier's operation.

Option B: Increase frequency & phase distortion is incorrect because negative feedback actually helps reduce both frequency and phase distortion. It enhances the fidelity of the amplifier by minimizing these distortions.

Option C: Reduces bandwidth is incorrect because negative feedback typically increases the bandwidth of an amplifier. It makes the amplifier more stable across a wider range of frequencies.

Option D: Increases noise is incorrect because negative feedback reduces the overall noise in an amplifier. By stabilizing the gain and reducing distortion, it typically lowers the noise figure of the amplifier.

Conclusion: The correct answer is Option A: Reduces gain because negative feedback decreases the amplifier's gain but improves its overall performance in terms of linearity, stability, and distortion reduction.