1.6. AMPLIFIERS
CLASSIFICATION OF OUTPUT STAGES
1. In amplifier circuits, what is the primary function of the output stage?
A. Voltage amplification
B. Current amplification
C. Frequency modulation
D. Phase shifting
Answer: B. Current amplification
Explanation:
The output stage in amplifier circuits is primarily responsible for providing current amplification to drive the load, such as a speaker or another device.
2. Which of the following is a characteristic of a Class A amplifier output stage?
A. High efficiency
B. Low distortion
C. Limited current flow during the entire cycle
D. Suitable for battery-operated devices
Answer: B. Low distortion
Explanation:
Class A amplifiers are known for low distortion but are less efficient due to continuous current flow throughout the entire input cycle.
3. In a Class B amplifier output stage, how is the conduction angle divided between two transistors to improve efficiency?
A. 360 degrees for each transistor
B. 180 degrees for each transistor
C. 120 degrees for each transistor
D. 90 degrees for each transistor
Answer: D. 90 degrees for each transistor
Explanation:
In a Class B amplifier output stage, each transistor conducts for 180 degrees, and the combination of two transistors achieves a total conduction angle of 360 degrees, improving efficiency.
4. What is the primary disadvantage of a Class B amplifier output stage?
A. Low efficiency
B. High distortion
C. Limited voltage gain
D. Continuous power dissipation
Answer: B. High distortion
Explanation:
Class B amplifiers suffer from high distortion, especially at the crossover point where one transistor hands over to the other.
5. In a Class AB amplifier output stage, what is the key improvement over Class B in terms of conduction angle?
A. Full conduction angle
B. 180 degrees conduction angle
C. 120 degrees conduction angle
D. 90 degrees conduction angle
Answer: A. Full conduction angle
Explanation:
Class AB amplifiers offer a full conduction angle, which is an improvement over Class B, resulting in reduced distortion compared to pure Class B designs.
6. Which Class of amplifier output stage combines the efficiency of Class B and the low distortion of Class A?
A. Class A
B. Class B
C. Class AB
D. Class C
Answer: C. Class AB
Explanation:
Class AB amplifiers combine the efficiency of Class B and the low distortion of Class A, making them suitable for a wide range of applications.
7. What is the primary advantage of a Class D amplifier output stage?
A. High efficiency
B. Low distortion
C. Linear operation
D. Low power dissipation
Answer: A. High efficiency
Explanation:
Class D amplifiers achieve high efficiency by rapidly switching the output transistors between fully on and fully off states.
8. In a Class C amplifier output stage, what is a common application due to its inherent non-linear operation?
A. Audio amplification
B. Radio frequency amplification
C. Power supply regulation
D. Instrumentation amplification
Answer: B. Radio frequency amplification
Explanation:
Class C amplifiers, with their non-linear operation, are commonly used in radio frequency amplification where efficiency is crucial.
9. What is a characteristic of a Class H amplifier output stage?
A. Low efficiency
B. Fixed supply voltage
C. Variable supply voltage
D. Low distortion
Answer: C. Variable supply voltage
Explanation:
Class H amplifiers use a variable supply voltage to improve efficiency by adjusting the voltage based on the input signal, reducing power dissipation.
10. In a bridged amplifier configuration, how are the load and power distributed between two amplifiers?
A. Load is shared, and power is combined
B. Load is combined, and power is shared
C. Load and power are both shared
D. Load and power are both combined
Answer: B. Load is combined, and power is shared
Explanation:
In a bridged amplifier configuration, the load is combined, resulting in higher efficiency, and power is shared between the two amplifiers.
CLASS A OUTPUT STAGE
1. What is the primary characteristic of a Class A amplifier output stage?
A. High efficiency
B. Low distortion
C. Limited conduction angle
D. Reduced power dissipation
Answer: B. Low distortion
Explanation:
Class A amplifiers are known for low distortion due to their full conduction angle and continuous current flow throughout the entire input cycle.
2. In a Class A amplifier output stage, what percentage of the input cycle does each transistor conduct?
A. 25%
B. 50%
C. 75%
D. 100%
Answer: D. 100%
Explanation:
In a Class A amplifier output stage, each transistor conducts for the entire input cycle, providing a full 360 degrees conduction angle.
3. What is a significant drawback of Class A amplifiers in terms of efficiency?
A. High power dissipation
B. Limited voltage gain
C. High distortion
D. Limited bandwidth
Answer: A. High power dissipation
Explanation:
Class A amplifiers are known for high power dissipation as they continuously draw current, making them less efficient compared to other classes.
4. What is the primary advantage of using a Class A amplifier in audio applications?
A. High efficiency
B. Low power dissipation
C. Low distortion
D. Wide bandwidth
Answer: C. Low distortion
Explanation:
Class A amplifiers are favored in audio applications due to their low distortion, providing clean and accurate signal reproduction.
5. In a Class A push-pull amplifier configuration, how are the output transistors biased?
A. One transistor is biased for Class A, and the other for Class B.
B. Both transistors are biased for Class A operation.
C. Both transistors are biased for Class B operation.
D. One transistor is biased for Class B, and the other for Class A.
Answer: B. Both transistors are biased for Class A operation.
Explanation:
In a Class A push-pull configuration, both output transistors are biased for Class A operation to eliminate crossover distortion.
6. What is the primary role of the biasing arrangement in a Class A amplifier output stage?
A. To maximize efficiency
B. To minimize distortion
C. To control voltage gain
D. To limit power dissipation
Answer: D. To limit power dissipation
Explanation:
The biasing arrangement in a Class A amplifier output stage is designed to limit power dissipation by keeping the transistors in the active region.
7. How does the power supply voltage affect the efficiency of a Class A amplifier?
A. Higher power supply voltage increases efficiency.
B. Lower power supply voltage increases efficiency.
C. Power supply voltage has no impact on efficiency.
D. Efficiency remains constant regardless of power supply voltage.
Answer: B. Lower power supply voltage increases efficiency.
Explanation:
Lowering the power supply voltage in a Class A amplifier can increase efficiency by reducing power dissipation.
8. What is a common application of Class A amplifiers in addition to audio amplification?
A. Radio frequency amplification
B. Power supply regulation
C. Instrumentation amplification
D. Digital signal processing
Answer: C. Instrumentation amplification
Explanation:
Class A amplifiers are commonly used in instrumentation applications where low distortion and precision amplification are crucial.
9. Why are Class A amplifiers less commonly used in high-power applications?
A. High distortion
B. Limited voltage gain
C. High power dissipation
D. Limited bandwidth
Answer: C. High power dissipation
Explanation:
Class A amplifiers are less commonly used in high-power applications due to their high power dissipation, which can result in excessive heat.
10. What is the impact of temperature variations on a Class A amplifier's biasing arrangement?
A. Temperature has no impact on biasing.
B. Higher temperatures decrease biasing stability.
C. Higher temperatures increase biasing stability.
D. Lower temperatures decrease biasing stability.
Answer: B. Higher temperatures decrease biasing stability.
Explanation:
Higher temperatures can decrease the stability of the biasing arrangement in a Class A amplifier, potentially leading to changes in operating conditions and performance.
CLASS B OUTPUT STAGE
1. What is a key characteristic of a Class B amplifier output stage?
A. High efficiency
B. Low distortion
C. Continuous current flow
D. Full conduction angle
Answer: A. High efficiency
Explanation:
Class B amplifiers are known for high efficiency as each transistor conducts only for half of the input cycle, reducing power dissipation.
2. In a Class B amplifier output stage, how is the conduction angle distributed between two transistors to cover the entire cycle?
A. 180 degrees for each transistor
B. 90 degrees for each transistor
C. 120 degrees for each transistor
D. 360 degrees for each transistor
Answer: A. 180 degrees for each transistor
Explanation:
In a Class B amplifier, each transistor conducts for 180 degrees, and the combination of two transistors covers the entire 360-degree input cycle.
3. What is the main disadvantage of a Class B amplifier in terms of distortion?
A. High distortion at crossover points
B. Low distortion throughout the cycle
C. No distortion
D. Distortion is frequency-dependent
Answer: A. High distortion at crossover points
Explanation:
Class B amplifiers suffer from high distortion, especially at the crossover points where one transistor hands over to the other, causing a momentary gap in conduction.
4. What is a common application of Class B amplifiers due to their efficiency?
A. Audio amplification
B. Radio frequency amplification
C. Instrumentation amplification
D. Power supply regulation
Answer: B. Radio frequency amplification
Explanation:
Class B amplifiers are commonly used in radio frequency amplification applications where high efficiency is crucial.
5. In a Class B push-pull amplifier configuration, how are the transistors biased to eliminate crossover distortion?
A. One transistor is biased for Class A, and the other for Class B.
B. Both transistors are biased for Class A operation.
C. Both transistors are biased for Class B operation.
D. One transistor is biased for Class B, and the other for Class A.
Answer: B. Both transistors are biased for Class A operation.
Explanation:
In a Class B push-pull configuration, both output transistors are biased for Class A operation to eliminate crossover distortion.
6. What is the efficiency of a Class B amplifier in theory?
A. 25%
B. 50%
C. 75%
D. 100%
Answer: B. 50%
Explanation:
Theoretical maximum efficiency of a Class B amplifier is 50%, as each transistor conducts for half of the input cycle.
7. Why is a small amount of Class A biasing sometimes added to Class B amplifiers?
A. To increase efficiency
B. To decrease efficiency
C. To eliminate crossover distortion
D. To increase power dissipation
Answer: C. To eliminate crossover distortion
Explanation:
A small amount of Class A biasing is added to Class B amplifiers to eliminate crossover distortion and improve overall linearity.
8. What is a disadvantage of Class B amplifiers in terms of power dissipation during no-signal periods?
A. High power dissipation
B. Low power dissipation
C. No power dissipation
D. Variable power dissipation
Answer: C. No power dissipation
Explanation:
Class B amplifiers experience no power dissipation during no-signal periods due to the cutoff of both transistors, contributing to their high efficiency.
9. In a Class B amplifier, what is the output waveform like when there is no input signal?
A. Distorted sine wave
B. Triangular wave
C. Square wave
D. No output
Answer: D. No output
Explanation:
In a Class B amplifier with no input signal, both transistors are cutoff, resulting in no output.
10. What is a typical application of Class B amplifiers in audio systems?
A. High-fidelity audio amplification
B. Low-power headphone amplification
C. Public address systems
D. Instrumentation amplification
Answer: C. Public address systems
Explanation:
Class B amplifiers are commonly used in public address systems where efficiency is important, and the occasional crossover distortion may be tolerable.
CLASS AB OUTPUT STAGE
1. What is a key characteristic of a Class AB amplifier output stage?
A. High efficiency
B. Low distortion
C. Continuous current flow
D. Full conduction angle
Answer: B. Low distortion
Explanation:
Class AB amplifiers aim to combine the low distortion of Class A amplifiers with the higher efficiency of Class B amplifiers.
2. In a Class AB amplifier output stage, how is the conduction angle distributed between two transistors?
A. 180 degrees for each transistor
B. 90 degrees for each transistor
C. 120 degrees for each transistor
D. 360 degrees for each transistor
Answer: C. 120 degrees for each transistor
Explanation:
In a Class AB amplifier, each transistor conducts for a portion of the input cycle, typically around 120 degrees, resulting in reduced crossover distortion.
3. Why is a Class AB amplifier considered more efficient than a pure Class A amplifier?
A. Continuous current flow
B. Lower power dissipation
C. Reduced crossover distortion
D. Full conduction angle
Answer: B. Lower power dissipation
Explanation:
Class AB amplifiers achieve higher efficiency compared to pure Class A amplifiers by reducing power dissipation through partial cutoff of the output transistors.
4. What is the primary advantage of using a Class AB amplifier in audio applications?
A. High efficiency
B. Low power dissipation
C. Low distortion
D. Wide bandwidth
Answer: D. Wide bandwidth
Explanation:
Class AB amplifiers are favored in audio applications due to their wide bandwidth, making them suitable for reproducing a broad range of frequencies.
5. In a Class AB push-pull amplifier configuration, how are the transistors biased to reduce crossover distortion?
A. One transistor is biased for Class A, and the other for Class B.
B. Both transistors are biased for Class A operation.
C. Both transistors are biased for Class B operation.
D. One transistor is biased for Class B, and the other for Class A.
Answer: B. Both transistors are biased for Class A operation.
Explanation:
In a Class AB push-pull configuration, both output transistors are biased for Class A operation to minimize crossover distortion.
6. How does the biasing arrangement in a Class AB amplifier differ from that in a pure Class B amplifier?
A. Class AB uses no biasing.
B. Class AB uses fixed biasing.
C. Class AB uses variable biasing.
D. Class AB uses dynamic biasing.
Answer: C. Class AB uses variable biasing.
Explanation:
Class AB amplifiers use variable biasing, where a small amount of bias is applied to ensure one transistor conducts slightly even when the signal is small, reducing crossover distortion.
7. What happens to the efficiency of a Class AB amplifier as the biasing increases?
A. Efficiency decreases.
B. Efficiency remains constant.
C. Efficiency increases.
D. Efficiency becomes unpredictable.
Answer: A. Efficiency decreases.
Explanation:
As the biasing increases in a Class AB amplifier, the efficiency decreases because more power is dissipated in the output transistors.
8. What is a common application of Class AB amplifiers in addition to audio amplification?
A. Radio frequency amplification
B. Power supply regulation
C. Instrumentation amplification
D. Digital signal processing
Answer: A. Radio frequency amplification
Explanation:
Class AB amplifiers find applications in radio frequency amplification where a balance between efficiency and distortion is important.
9. Why are Class AB amplifiers more suitable for high-power applications compared to Class A amplifiers?
A. Lower distortion
B. Higher efficiency
C. Reduced power dissipation
D. Wide bandwidth
Answer: B. Higher efficiency
Explanation:
Class AB amplifiers are more suitable for high-power applications due to their higher efficiency, which results in less power dissipation and reduced heat generation.
10. What is the impact of temperature variations on a Class AB amplifier's biasing arrangement?
A. Temperature has no impact on biasing.
B. Higher temperatures decrease biasing stability.
C. Higher temperatures increase biasing stability.
D. Lower temperatures decrease biasing stability.
Answer: B. Higher temperatures decrease biasing stability.
Explanation:
Higher temperatures can decrease the stability of the biasing arrangement in a Class AB amplifier, potentially leading to changes in operating conditions and performance.
BIASING THE CLASS AB STAGES
1. What is the primary purpose of biasing in a Class AB amplifier stage?
A. To maximize efficiency
B. To minimize distortion
C. To control voltage gain
D. To limit power dissipation
Answer: B. To minimize distortion
Explanation:
Biasing in a Class AB amplifier stage is essential to minimize crossover distortion and achieve low distortion in the output signal.
2. Which biasing method is commonly used in Class AB amplifiers to ensure a small quiescent current flows through the transistors even when there is no input signal?
A. Fixed bias
B. Collector-to-base bias
C. Emitter bias
D. Voltage-divider bias
Answer: C. Emitter bias
Explanation:
Emitter bias is commonly used in Class AB amplifiers to establish a small quiescent current, ensuring both transistors remain in the active region.
3. What is the advantage of using a biasing arrangement that provides a small quiescent current in a Class AB amplifier?
A. Increased efficiency
B. Lower power dissipation
C. Reduced crossover distortion
D. Greater voltage gain
Answer: C. Reduced crossover distortion
Explanation:
A small quiescent current in the biasing arrangement helps reduce crossover distortion in Class AB amplifiers, improving overall linearity.
4. What happens to the quiescent current in a Class AB amplifier if the biasing is too high?
A. Quiescent current increases.
B. Quiescent current decreases.
C. Quiescent current remains constant.
D. Quiescent current becomes unpredictable.
Answer: A. Quiescent current increases.
Explanation:
If the biasing is too high in a Class AB amplifier, the quiescent current increases, leading to higher power dissipation and reduced efficiency.
5. Why is it important to set the biasing point in the active region for both transistors in a Class AB amplifier?
A. To maximize efficiency
B. To minimize distortion
C. To control voltage gain
D. To limit power dissipation
Answer: B. To minimize distortion
Explanation:
Setting the biasing point in the active region for both transistors helps minimize distortion, especially at the crossover points where the signal transitions between transistors.
6. What is the risk of setting the biasing too close to the cutoff region in a Class AB amplifier?
A. Higher efficiency
B. Lower distortion
C. Increased crossover distortion
D. Greater voltage gain
Answer: C. Increased crossover distortion
Explanation:
Setting the biasing too close to the cutoff region can lead to increased crossover distortion in a Class AB amplifier, impacting the linearity of the output signal.
7. Which biasing method provides stability in the quiescent point for a Class AB amplifier, compensating for temperature variations?
A. Fixed bias
B. Collector-to-base bias
C. Emitter bias
D. Voltage-divider bias
Answer: D. Voltage-divider bias
Explanation:
Voltage-divider bias is known for providing stability in the quiescent point, compensating for temperature variations in a Class AB amplifier.
8. How does temperature variation impact the stability of a fixed bias arrangement in a Class AB amplifier?
A. Temperature has no impact on bias stability.
B. Higher temperatures decrease bias stability.
C. Higher temperatures increase bias stability.
D. Lower temperatures decrease bias stability.
Answer: B. Higher temperatures decrease bias stability.
Explanation:
In a fixed bias arrangement, higher temperatures can decrease the stability of the bias point in a Class AB amplifier, affecting its performance.
9. What is the function of a thermal compensation circuit in a Class AB amplifier?
A. To maximize efficiency
B. To minimize distortion
C. To control voltage gain
D. To compensate for temperature variations
Answer: D. To compensate for temperature variations
Explanation:
A thermal compensation circuit in a Class AB amplifier helps maintain stability and compensate for variations in bias due to changes in temperature.
10. In a Class AB amplifier, why is it crucial to consider the trade-off between biasing and power dissipation?
A. To maximize efficiency
B. To minimize distortion
C. To control voltage gain
D. To balance efficiency and heat generation
Answer: D. To balance efficiency and heat generation
Explanation:
Balancing biasing and power dissipation is crucial in a Class AB amplifier to achieve a trade-off between efficiency and heat generation, ensuring reliable operation.
POWER BJTs
1. What is the primary purpose of using Power Bipolar Junction Transistors (BJTs) in electronic circuits?
A. Voltage amplification
B. Current amplification
C. Frequency modulation
D. Phase shifting
Answer: B. Current amplification
Explanation:
Power BJTs are commonly used for their ability to provide current amplification, making them suitable for power amplifier applications.
2. What distinguishes Power BJTs from small-signal BJTs?
A. Higher power dissipation
B. Lower voltage gain
C. Reduced current carrying capacity
D. Smaller physical size
Answer: A. Higher power dissipation
Explanation:
Power BJTs are designed to handle higher power dissipation compared to small-signal BJTs, allowing them to handle larger currents and voltages.
3. In a Power BJT, what is the significance of the breakdown voltage rating?
A. Maximum voltage across the collector
B. Maximum voltage across the base
C. Maximum voltage across the emitter
D. Maximum voltage across the collector-base junction
Answer: A. Maximum voltage across the collector
Explanation:
The breakdown voltage rating of a Power BJT indicates the maximum voltage that can be applied across the collector without causing a breakdown.
4. What is the typical range of collector currents for Power BJTs in power amplifier applications?
A. Microamperes
B. Milliamperes
C. Amperes
D. Kilamperes
Answer: C. Amperes
Explanation:
Power BJTs are capable of handling collector currents in the range of amperes, making them suitable for high-power applications.
5. Why is thermal management crucial in Power BJT applications?
A. To increase voltage gain
B. To minimize distortion
C. To prevent overheating
D. To reduce current flow
Answer: C. To prevent overheating
Explanation:
Power BJTs can generate significant heat during operation, and proper thermal management is essential to prevent overheating and ensure reliable performance.
6. What is the role of the heat sink in Power BJT circuits?
A. To amplify the signal
B. To provide thermal insulation
C. To increase breakdown voltage
D. To dissipate heat
Answer: D. To dissipate heat
Explanation:
The heat sink in Power BJT circuits is designed to dissipate heat generated during operation, preventing overheating and ensuring stable performance.
7. What does the Safe Operating Area (SOA) of a Power BJT represent?
A. Maximum temperature limit
B. Maximum current-voltage combinations
C. Minimum breakdown voltage
D. Minimum power dissipation
Answer: B. Maximum current-voltage combinations
Explanation:
The Safe Operating Area (SOA) of a Power BJT defines the safe combinations of collector current and collector-emitter voltage to prevent device damage.
8. In a Power BJT, what is the purpose of the base drive circuit?
A. To control voltage gain
B. To minimize distortion
C. To amplify the signal
D. To provide proper biasing
Answer: D. To provide proper biasing
Explanation:
The base drive circuit in a Power BJT is responsible for providing the proper biasing to ensure the transistor operates in its active region.
9. How does the current gain (β) of a Power BJT differ from that of a small-signal BJT?
A. Power BJTs have higher β values.
B. Power BJTs have lower β values.
C. β values are the same for both.
D. β values depend on temperature.
Answer: B. Power BJTs have lower β values.
Explanation:
Power BJTs typically have lower current gain (β) values compared to small-signal BJTs.
10. What is a common application of Power BJTs in electronic systems?
A. Low-power audio amplification
B. RF signal processing
C. High-power audio amplification
D. Digital signal processing
Answer: C. High-power audio amplification
Explanation:
Power BJTs are commonly used in high-power audio amplifiers to deliver significant current and voltage for driving speakers and other loads in audio systems.
TRANSFORMER COUPLED PUSH -PULL STAGES
1. What is the primary advantage of using a transformer-coupled push-pull stage in amplifier circuits?
A. Voltage amplification
B. Current amplification
C. Phase modulation
D. Frequency shifting
Answer: B. Current amplification
Explanation:
The primary advantage of a transformer-coupled push-pull stage is current amplification, which makes it suitable for power amplifier applications.
2. In a transformer-coupled push-pull amplifier, how are the two output transistors biased to reduce crossover distortion?
A. One transistor is biased for Class A, and the other for Class B.
B. Both transistors are biased for Class A operation.
C. Both transistors are biased for Class B operation.
D. One transistor is biased for Class B, and the other for Class A.
Answer: B. Both transistors are biased for Class A operation.
Explanation:
In a transformer-coupled push-pull configuration, both output transistors are biased for Class A operation to minimize crossover distortion.
3. What is the role of the transformer in a transformer-coupled push-pull stage?
A. To block DC components
B. To provide voltage amplification
C. To enhance impedance matching
D. To amplify the signal
Answer: C. To enhance impedance matching
Explanation:
The transformer in a transformer-coupled push-pull stage helps enhance impedance matching between the amplifier and the load.
4. How does the center-tapped primary winding of the transformer assist in push-pull operation?
A. It provides voltage amplification.
B. It blocks DC components.
C. It balances the push-pull operation.
D. It enhances power dissipation.
Answer: C. It balances the push-pull operation.
Explanation:
The center-tapped primary winding helps balance the push-pull operation, ensuring equal and opposite currents flow through the two halves of the winding.
5. What happens if there is an imbalance in the push-pull operation of a transformer-coupled amplifier stage?
A. Increased efficiency
B. Decreased efficiency
C. Higher power dissipation
D. Lower power dissipation
Answer: C. Higher power dissipation
Explanation:
An imbalance in the push-pull operation can lead to higher power dissipation and reduced efficiency in a transformer-coupled amplifier stage.
6. How does the turns ratio of the transformer affect voltage gain in a transformer-coupled push-pull amplifier?
A. Higher turns ratio results in higher voltage gain.
B. Lower turns ratio results in higher voltage gain.
C. Turns ratio has no impact on voltage gain.
D. Variable turns ratio results in variable voltage gain.
Answer: A. Higher turns ratio results in higher voltage gain.
Explanation:
A higher turns ratio in the transformer increases voltage gain in a transformer-coupled push-pull amplifier.
7. What is the primary drawback of using transformers in amplifier circuits?
A. Low cost
B. Heavy weight
C. Limited voltage gain
D. Increased efficiency
Answer: B. Heavy weight
Explanation:
The primary drawback of using transformers is their relatively heavy weight, which can impact portability and practicality in certain applications.
8. In a transformer-coupled push-pull stage, why is thermal management crucial?
A. To increase voltage gain
B. To minimize distortion
C. To prevent overheating
D. To reduce current flow
Answer: C. To prevent overheating
Explanation:
Proper thermal management is crucial to prevent overheating in a transformer-coupled push-pull stage and ensure stable performance.
9. What is the function of the transformer's secondary winding in a transformer-coupled push-pull amplifier?
A. To balance the push-pull operation
B. To block DC components
C. To enhance impedance matching
D. To amplify the signal
Answer: B. To block DC components
Explanation:
The secondary winding of the transformer blocks DC components, allowing only the AC component to be transferred to the load.
10. In a transformer-coupled push-pull amplifier, how does the transformer assist in impedance matching between the amplifier and the load?
A. By blocking DC components
B. By providing a center-tapped winding
C. By adjusting the turns ratio
D. By enhancing power transfer
Answer: C. By adjusting the turns ratio
Explanation:
The turns ratio of the transformer can be adjusted to optimize impedance matching between the amplifier and the load in a transformer-coupled push-pull stage.
TUNED AMPLIFIER
1. What is the primary function of a tuned amplifier in electronic circuits?
A. Voltage amplification
B. Frequency selection
C. Phase modulation
D. Current amplification
Answer: B. Frequency selection
Explanation:
The primary function of a tuned amplifier is to select and amplify signals at a specific resonant frequency.
2. What type of circuit is commonly used for tuning in tuned amplifiers?
A. Capacitive circuit
B. Inductive circuit
C. Resistive circuit
D. LC circuit
Answer: D. LC circuit
Explanation:
LC circuits, consisting of inductance (L) and capacitance (C), are commonly used for tuning in tuned amplifiers.
3. In a tuned amplifier, what is the significance of the resonant frequency?
A. Maximum voltage gain
B. Minimum distortion
C. Maximum current flow
D. Frequency at which amplification occurs
Answer: D. Frequency at which amplification occurs
Explanation:
The resonant frequency in a tuned amplifier is the frequency at which maximum amplification occurs.
4. How does a tuned amplifier enhance the selectivity of signals?
A. By increasing bandwidth
B. By decreasing bandwidth
C. By amplifying all frequencies equally
D. By amplifying a specific range of frequencies
Answer: D. By amplifying a specific range of frequencies
Explanation:
A tuned amplifier selectively amplifies signals within a specific frequency range, enhancing selectivity.
5. What is the typical configuration of a tuned amplifier circuit for audio applications?
A. Parallel-tuned amplifier
B. Series-tuned amplifier
C. Double-tuned amplifier
D. Triple-tuned amplifier
Answer: C. Double-tuned amplifier
Explanation:
Double-tuned amplifiers are commonly used in audio applications to achieve narrow bandpass characteristics.
6. What is the purpose of coupling capacitors in tuned amplifier circuits?
A. To block DC components
B. To increase resonant frequency
C. To provide voltage amplification
D. To decrease selectivity
Answer: A. To block DC components
Explanation:
Coupling capacitors in tuned amplifier circuits block DC components, allowing only the AC signals to pass through.
7. In a tuned amplifier, what is the role of the bandwidth?
A. To determine the resonant frequency
B. To limit the frequency range
C. To maximize distortion
D. To minimize voltage gain
Answer: B. To limit the frequency range
Explanation:
The bandwidth in a tuned amplifier determines the range of frequencies over which amplification occurs and contributes to the selectivity of the circuit.
8. What is the primary disadvantage of a narrow bandwidth in a tuned amplifier?
A. Reduced selectivity
B. Increased distortion
C. Higher efficiency
D. Greater voltage gain
Answer: A. Reduced selectivity
Explanation:
A narrow bandwidth may reduce selectivity in a tuned amplifier, making it less effective in filtering out unwanted frequencies.
9. How does the quality factor (Q) of a tuned amplifier relate to its selectivity?
A. Higher Q results in higher selectivity.
B. Higher Q results in lower selectivity.
C. Q has no impact on selectivity.
D. Q determines bandwidth, not selectivity.
Answer: A. Higher Q results in higher selectivity.
Explanation:
A higher quality factor (Q) in a tuned amplifier results in higher selectivity, as it narrows the bandwidth.
10. In a tuned amplifier circuit, how does the addition of more tuned circuits affect selectivity and bandwidth?
A. Increases selectivity, decreases bandwidth
B. Decreases selectivity, increases bandwidth
C. Has no impact on selectivity and bandwidth
D. Simultaneously increases selectivity and bandwidth
Answer: A. Increases selectivity, decreases bandwidth
Explanation:
Adding more tuned circuits in a series tends to increase selectivity and decrease bandwidth in a tuned amplifier.
OP-AMPS
1. What does the term "OP AMP" stand for in electronics?
A. Operational Amplifier
B. Output Power Amplifier
C. Oscillating Phase Amplifier
D. Optimal Performance Amplifier
Answer: A. Operational Amplifier
Explanation:
OP AMP stands for Operational Amplifier, which is a versatile and widely used electronic component.
2. What is the typical input impedance of an ideal operational amplifier (OP AMP)?
A. Infinite
B. Zero
C. Variable
D. One
Answer: A. Infinite
Explanation:
An ideal OP AMP has infinite input impedance, meaning it draws negligible current from the input source.
3. In an ideal OP AMP, what is the relationship between the inverting and non-inverting input terminals?
A. Inverting input is at a higher voltage
B. Non-inverting input is at a higher voltage
C. Inverting and non-inverting inputs are at the same voltage
D. The relationship depends on the power supply voltage
Answer: C. Inverting and non-inverting inputs are at the same voltage
Explanation:
In an ideal OP AMP, the inputs draw negligible current, and the inverting and non-inverting inputs are assumed to be at the same voltage.
4. What is the primary function of the differential amplifier stage in an OP AMP?
A. Voltage amplification
B. Current amplification
C. Frequency modulation
D. Phase shifting
Answer: A. Voltage amplification
Explanation:
The differential amplifier stage in an OP AMP provides voltage amplification by amplifying the difference between the inverting and non-inverting inputs.
5. What is the purpose of the compensation capacitor in the internal circuitry of an OP AMP?
A. To block DC components
B. To provide voltage amplification
C. To stabilize the frequency response
D. To increase power dissipation
Answer: C. To stabilize the frequency response
Explanation:
The compensation capacitor is used to stabilize the frequency response of an OP AMP and ensure proper performance across a range of frequencies.
6. What is the open-loop gain of an OP AMP under ideal conditions?
A. Infinite
B. Zero
C. Variable
D. One
Answer: A. Infinite
Explanation:
Under ideal conditions, an OP AMP has infinite open-loop gain, meaning it can amplify input signals by an extremely large factor.
7. In a negative feedback configuration, how does it affect the characteristics of an OP AMP?
A. Increases stability and reduces gain
B. Increases gain and reduces stability
C. Has no impact on stability or gain
D. Reduces both stability and gain
Answer: A. Increases stability and reduces gain
Explanation:
Negative feedback in an OP AMP increases stability and reduces gain, making the amplifier more predictable and controllable.
8. What is the purpose of the offset voltage adjustment in some OP AMPs?
A. To increase input impedance
B. To balance the inverting and non-inverting inputs
C. To compensate for input offset voltage
D. To increase power supply voltage
Answer: C. To compensate for input offset voltage
Explanation:
The offset voltage adjustment in some OP AMPs is used to compensate for any voltage difference between the inverting and non-inverting inputs.
9. In an OP AMP circuit, what is the significance of the common-mode rejection ratio (CMRR)?
A. Determines bandwidth
B. Indicates voltage gain
C. Measures stability
D. Represents the ability to reject common-mode signals
Answer: D. Represents the ability to reject common-mode signals
Explanation:
The CMRR of an OP AMP indicates its ability to reject common-mode signals, which are signals that appear on both the inverting and non-inverting inputs.
10. What is the output voltage of an inverting amplifier configuration when a positive voltage is applied to the inverting input?
A. Positive and equal to the input voltage
B. Positive and amplified
C. Negative and equal to the input voltage
D. Negative and inverted
Answer: D. Negative and inverted
Explanation:
In an inverting amplifier configuration, a positive voltage applied to the inverting input results in a negative and inverted output voltage.