Chapter 5: Power Amplifiers Quiz
48 Questions
3 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the conduction angle for a Class A power amplifier?

  • Less than 180°
  • 360° (correct)
  • 90°
  • 180°

    • What is the maximum efficiency of a Class A power amplifier?

  • 100%
  • 50%
  • 25% (correct)
  • 78.5%

    • What characteristic of a Class A amplifier allows it to conduct over the entire input signal cycle?

  • It operates with a conduction angle of 90°.
  • It only conducts during positive cycles.
  • It is biased at half of the supply voltage. (correct)
  • It has high maximum efficiency.

    • What is the maximum efficiency of a Class A amplifier?

    <p>25%</p> Signup and view all the answers

    Which class of amplifier has an output wave that is 180° out of phase with the input?

    <p>Class A</p> Signup and view all the answers

    In which amplifier class does the transistor conduct over only half of the input signal cycle?

    <p>Class B</p> Signup and view all the answers

    What is the operating cycle for a Class B amplifier?

    <p>180°</p> Signup and view all the answers

    What is the relationship between the load line and the Q-point in a Class A amplifier?

    <p>The Q-point must be centered on the load line</p> Signup and view all the answers

    What is the primary basis for classifying amplifiers into different classes?

    <p>Construction and operating characteristics</p> Signup and view all the answers

    What conduction angle does a Class B amplifier operate at?

    <p>180°</p> Signup and view all the answers

    Which class of amplifier typically has a power efficiency greater than 90%?

    <p>Class C</p> Signup and view all the answers

    In terms of power efficiency, which amplifier class falls between 25% and 78.5%?

    <p>Class AB</p> Signup and view all the answers

    Which statement accurately describes a Class A amplifier?

    <p>It transmits both positive and negative cycles equally.</p> Signup and view all the answers

    What is the conduction angle of a Class C amplifier?

    <p>Less than 180°</p> Signup and view all the answers

    How does the Q-point relate to Class A amplifiers?

    <p>It is biased to ensure $I_{CQ} &gt; I_{s max}$.</p> Signup and view all the answers

    What is a key benefit of Class B amplifiers compared to Class A amplifiers?

    <p>Higher power efficiency.</p> Signup and view all the answers

    What is the purpose of biasing a transistor in a series-fed Class A amplifier?

    <p>To allow for maximum output voltage swing</p> Signup and view all the answers

    What does the collector current in a Class A amplifier depend on?

    <p>Base-bias current and the transistor's beta</p> Signup and view all the answers

    In a Class A amplifier, what is the relationship between collector-emitter voltage (VCE) and collector current (IC)?

    <p>VCE decreases as IC increases</p> Signup and view all the answers

    What is the overall efficiency of a Class A amplifier compared to other classes of amplifiers?

    <p>Generally lower than other amplifier classes</p> Signup and view all the answers

    Why is it important to allow the output to vary through a full VCC volts peak-to-peak in a Class A amplifier?

    <p>To allow for a full cycle of input sine wave operation</p> Signup and view all the answers

    What formula represents the DC base-bias current in a Class A amplifier?

    <p>$I_B = V_{CC} - 0.7 ΤR_B$</p> Signup and view all the answers

    What does the power drawn from the supply in a Class A amplifier represent?

    <p>Active power consumed by the amplifier</p> Signup and view all the answers

    What impact does a larger collector resistor (RC) have on a Class A amplifier's performance?

    <p>Results in lower output power</p> Signup and view all the answers

    What type of transistors are used in a Class B push-pull amplifier?

    <p>One npn and one pnp transistor</p> Signup and view all the answers

    What issue does crossover distortion cause in a Class B amplifier?

    <p>Distortion in the output waveform</p> Signup and view all the answers

    How is a Class AB amplifier biased compared to a Class B amplifier?

    <p>Slightly above cutoff</p> Signup and view all the answers

    What is a primary advantage of Class AB amplifiers over Class B amplifiers?

    <p>Elimination of crossover distortion</p> Signup and view all the answers

    What happens when the DC base voltage is zero in a Class B amplifier?

    <p>Both transistors are off</p> Signup and view all the answers

    What is the effect of adjusting the biasing in a Class AB amplifier?

    <p>Allows slight conduction even with no input</p> Signup and view all the answers

    In a Class B push-pull configuration, what is meant by 'transformer coupling'?

    <p>Using transformers to connect the stages</p> Signup and view all the answers

    What defines the operation of complementary symmetry transistors in a Class B amplifier?

    <p>They conduct on opposite alternations of the input cycle</p> Signup and view all the answers

    What is the primary characteristic of Class C amplifiers regarding conduction?

    <p>Conduction occurs for much less than 180 degrees.</p> Signup and view all the answers

    Why are Class C amplifiers not suitable for linear amplification?

    <p>Their output amplitude is a nonlinear function of the input.</p> Signup and view all the answers

    What type of load is a Class C amplifier typically operated with?

    <p>Resonant circuit load</p> Signup and view all the answers

    During which event does the transistor in a Class C amplifier turn on?

    <p>When the peak value exceeds the barrier potential.</p> Signup and view all the answers

    What does the power dissipation equation for a Class C amplifier represent in terms of operation?

    <p>The average power dissipation during the entire cycle.</p> Signup and view all the answers

    In tuned Class C operation, how is the collector voltage characterized?

    <p>It is not a replica of the input signal.</p> Signup and view all the answers

    How does the efficiency of Class C amplifiers compare to Class A, B, or AB amplifiers?

    <p>It is more efficient than all classes.</p> Signup and view all the answers

    For what purpose is the resistive load used in a Class C amplifier's operation?

    <p>To illustrate the operational concept.</p> Signup and view all the answers

    What is the primary function of using equal values of R1 and R2 in the voltage-divider arrangement?

    <p>To force the voltage at point A to equal 0 V</p> Signup and view all the answers

    In a Class B amplifier, what happens to the transistors when there is no input signal?

    <p>They have only a very small current</p> Signup and view all the answers

    How does the Q-point of a Class A amplifier differ from that of a Class B amplifier?

    <p>It is near the middle of the output characteristics</p> Signup and view all the answers

    What is the ideal maximum peak output voltage estimated to be in a Class B amplifier?

    <p>$V_{CC}$</p> Signup and view all the answers

    What condition allows the current in the diodes D1 and D2 to match the current in the transistor BE junctions?

    <p>Having closely matched diode characteristics</p> Signup and view all the answers

    What does the ac saturation current ($I_{c(sat)}$) expression imply in a class B amplifier?

    <p>$I_{c(sat)} = C imes R_L$</p> Signup and view all the answers

    What is a significant advantage of a Class B amplifier compared to a Class A amplifier?

    <p>Higher efficiency</p> Signup and view all the answers

    Which voltage represents the threshold for ac cutoff in a Class B amplifier?

    <p>$V_{CC}$</p> Signup and view all the answers

    Study Notes

    Chapter 5: Power Amplifiers

    • Power amplifiers are used in the final stage of communication receivers or transmitters to deliver signal power to devices like speakers or antennas.
    • Bipolar Junction Transistors (BJTs) are used to illustrate power amplifier principles.
    • Efficiency is a critical factor in power amplifiers to prevent excessive junction temperature or prolong battery life. Optimizing temperature range typically is 150-200°C for silicon junctions.
    • Linearity (or Total Harmonic Distortion (THD)) is important to maintain signal quality.
    • Amplifiers are classified by frequency capabilities (audio or radio frequency) and coupling methods (R-C, transformer, direct).
    • Voltage amplifiers primarily increase the input voltage with minimal current output.
    • Power amplifiers increase the input power with minimal change in voltage, used in applications requiring high power delivery (e.g. audio and radio frequency).
    • Power amplifiers and voltage amplifiers differ in current gain, voltage gain, heat dissipation, cooling, transistor size, base width and beta. (refer to relevant tables).
    • Large-signal amplifiers (power amplifiers) feature high efficiency, high power handling capability and proper impedance matching with output devices.
    • Amplifier classes represent the amount the output signal varies over one cycle of operation for a full cycle of input signal (class A, AB, B, C).
    • Class A amplifier operates in the linear region of the transistor's characteristic curves throughout the input cycle, with an efficiency of 25% to 50%. The output is 180° out of phase with the input.
    • Class B amplifier conducts for only half the input cycle.  The efficiency is up to 78.5%.
    • Class AB amplifier is biased slightly above cutoff and operates in the linear region for slightly more than 180° of the input cycle.  It eliminates crossover distortion found in pure class B amplifiers.
    • Class C amplifier is biased for operation at less than 180° of the input signal cycle, usually with a tuned (resonant) circuit, for high efficiency (greater than 90%).

    Transformer-Coupled Class-A Power Amplifiers

    • Voltage transformation: V₂/V₁ = N₂/N₁

    • Current transformation: I₂/I₁ = N₁/N₂

    • Impedance transformation: R₁/R₂ = (N₁/N₂)² = α²

    • The reflected impedance (R₁) is directly related to the square of the turns ratio (N₁/N₂).

    • Efficiency depends on both the load resistance (RL) and the collector resistance (Rc).

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    RF and Power Amplifier PDF

    Description

    Test your knowledge on power amplifiers as discussed in Chapter 5. This quiz covers the principles of power amplifiers using BJTs, their efficiency, linearity, and classification by frequency capabilities. Understand the distinctions between power and voltage amplifiers in communication systems.

    More Like This

    Electromechanical Energy Converters: Power Amplifiers and Motors
    22 questions

    Electromechanical Energy Converters: Power Amplifiers and Motors

    EruditeHolly avatar
    EruditeHolly
    Transistor Power Amplifiers Quiz
    38 questions

    Transistor Power Amplifiers Quiz

    TenaciousFeynman9892 avatar
    TenaciousFeynman9892
    Power Amplifiers Overview
    33 questions

    Power Amplifiers Overview

    ResponsiveKazoo9793 avatar
    ResponsiveKazoo9793
    Communication Systems Quiz
    43 questions

    Communication Systems Quiz

    BeneficialLimeTree avatar
    BeneficialLimeTree
    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser