1. Is a hole a kind of carrier? Does the hole move electrons when it conducts electricity? A: No, a hole is not a physical particle but rather a concept used to describe the absence of an electron in a semiconductor. When current flows, it's actually the movement of electrons in the opposite direction that contributes to conduction. 2. What ratio is generally doped in the intrinsic semiconductor when preparing an impurity semiconductor? A: Typically, impurities are added in a ratio of about one part per million (ppm) to create an extrinsic semiconductor. 3. What is an N-type semiconductor? What is a P-type semiconductor? What happens when two semiconductors are fabricated together? A: An N-type semiconductor has free electrons as its majority carriers, while a P-type semiconductor has holes as its majority carriers. When combined, they form a PN junction. 4. What are the main physical characteristics of the PN junction? A: The PN junction exhibits unidirectional conductivity and is highly sensitive to temperature changes. 5. What are the characteristics of semiconductor device manufacturing electronic devices compared with traditional vacuum electronic devices? A: Semiconductor devices offer better frequency response, smaller size, lower power consumption, and easier integration. They also have higher reliability and seismic resistance. However, they may have higher distortion and less stability compared to vacuum tubes. 6. What are intrinsic semiconductors and impurity semiconductors? A: Intrinsic semiconductors are pure materials like silicon or germanium. Impurity semiconductors are created by doping them with small amounts of other elements to alter their electrical properties. 7. What are the names of PN knots? A: Common terms include the space charge region, depletion layer, and barrier layer. 8. Is the voltage and current applied to the PN junction linear? Why does it have unidirectional conductivity? A: No, the relationship between voltage and current is non-linear. Under forward bias, the barrier layer thins, allowing current to flow exponentially. Under reverse bias, the barrier thickens, blocking most current. This gives the PN junction its unidirectional behavior. 9. Is there really no current when the reverse voltage is applied to the PN junction? A: There is a very small reverse leakage current due to minority carriers, but it is negligible under normal conditions. 10. What are the most basic technical parameters of a diode? A: Key parameters include maximum rectified current, reverse breakdown voltage, and forward voltage drop. 11. What are the main uses of diodes? A: Diodes are used for rectification, detection, voltage regulation, and switching applications. 12. How does the transistor control the collector current? A: The transistor controls the collector current through the base-emitter current, which modulates the flow of charge carriers between the emitter and collector. 13. Can I use two diodes to reverse each other to form a triode? Why? A: No, because a transistor has a specific structure with three regions (emitter, base, collector), whereas two diodes cannot replicate this configuration. 14. What is the penetration current of the triode? What effect does it have on the amplifier? A: Penetration current, or leakage current, occurs when the base is open. It is temperature-sensitive and can cause instability in the amplifier if not controlled. 15. What is the gate voltage of the triode? A: For a silicon transistor, the base-emitter voltage is typically around 0.7 volts, while for a germanium transistor, it is about 0.3 volts. 16. Does the amplification circuit amplify the electrical signal and the magnifying glass amplifies the object with the same meaning? A: No, the amplification circuit increases the amplitude of a signal, while a magnifying glass increases the apparent size of an object. 17. What are the basic bias conditions in an amplifier consisting of a triode? A: The emitter junction must be forward-biased, and the collector junction must be reverse-biased. 18. What areas is the triode input and output characteristic curve generally divided into? A: The curve is typically divided into active (amplification), saturation, and cutoff regions. 19. What are the basic configurations of the amplifier circuit? What are they? A: The common-emitter, common-base, and common-collector configurations are the three basic types. 20. In the common emitter amplifying circuit, what kinds of bias circuits are generally available? A: Common biasing methods include fixed bias, voltage divider bias, and emitter bias. 21. What is the significance of the determination of the static working point for the amplifier? A: A properly set Q-point ensures minimal distortion and optimal performance of the amplifier. 22. Where should the static working point of the amplifier normally be located on the triode input and output characteristic curve? A: It should be centered in the active region to allow maximum undistorted signal swing. 23. Should I treat the power supply and capacitors when drawing the DC path of the amplifier? A: Capacitors are treated as open circuits, and the power supply is considered an ideal voltage source. 24. Which amplifiers are suitable for the diagram of the amplifier? A: The diagram is commonly used for single-transistor amplifiers and push-pull power amplifiers. 25. What is the significance of the DC load line and AC load line in the schematic method of the amplifier? A: The DC load line helps determine the quiescent point, while the AC load line shows how the signal will behave under varying conditions. 26. How to evaluate the performance of the amplifier circuit? What are the main indicators? A: Key indicators include gain, input and output impedance, bandwidth, distortion, and signal-to-noise ratio. 27. Why is the unit of the voltage gain of the amplifier often used in decibels? What is the relationship between it and the multiple? A: Decibels simplify calculations and make large values more manageable. The relationship is: dB = 20 log(Vout/Vin). 28. Is the passband of the amplifier as wide as possible? Why? A: Not necessarily. The passband depends on the application; some circuits require narrow bands for filtering, while others need wider bands for broader signals. 29. What is the effect of the amplifier’s input and output resistance on the amplifier? A: High input resistance minimizes signal loss, and low output resistance maximizes signal delivery to the load. 30. When designing an amplifier, what is the value principle for the input and output resistors? A: Input resistance should be high, and output resistance should be low. 31. What are the general categories of distortion in the amplifier? A: Saturation, cutoff, nonlinear, and crossover distortion are common types. 32. What type of distortion occurs when the amplifier’s working point is too high? Too low? A: Too high causes saturation distortion; too low causes cutoff distortion. 33. What are the causes of nonlinear distortion of the amplifier? A: Nonlinear distortion occurs when the operating point is in the nonlinear region of the transistor’s characteristics. 34. What is the difference between the micro-variable equivalent circuit analysis method and the graphical method in the analysis of the amplifier? A: The micro-variable method provides precise calculations, while the graphical method offers intuitive insight into the operating point and distortion. 35. What are the general steps for analyzing the amplifier circuit using the micro-variable equivalent circuit analysis method? A: Calculate the Q-point, draw the AC equivalent circuit, and compute the gain, input, and output resistance. 36. What is the scope of application of the micro-variable equivalent circuit analysis method? A: It is suitable for any linear circuit where the components operate within their linear range. 37. What are the limitations of the micro-variable equivalent circuit analysis method? A: It only handles AC signals, cannot calculate the Q-point, and cannot analyze nonlinear distortion or maximum output. 38. What are the main factors affecting the stability of the working point of the amplifier? A: Temperature drift, power supply fluctuations, and component aging are the main causes. 39. What method is generally used to stabilize the working point in the common emitter amplifying circuit? A: Current series negative feedback is commonly used. 40. Why can't a single-tube amplifier circuit meet the requirements of multi-faceted performance? A: It lacks sufficient gain, and its input/output impedance is not optimized for different stages. 41. What is the basic purpose of the coupling circuit? A: To allow AC signals to pass between stages while isolating DC voltages. 42. How many ways do inter-stage coupling of multi-stage amplifier circuits? A: RC coupling, transformer coupling, and direct coupling are the main methods. 43. What is the total voltage gain of the multistage amplifier circuit? A: It is the product of the gains at each stage. 44. What is the input and output resistance of a multi-stage amplifier circuit? A: The input resistance of the first stage is the overall input, and the output resistance of the last stage is the overall output. 45. What are the special problems of direct coupled amplifier circuits? How to solve them? A: Zero drift is the main issue. Differential amplifiers are used to reduce this problem. 46. Why is the amplification circuit the most common in three levels? A: Three stages provide a good balance between gain and stability, avoiding excessive complexity. 47. What is zero drift? What are the main reasons for this? What is the most fundamental one? A: Zero drift is a slow change in output when no signal is present. It is mainly caused by temperature changes, which affect the Q-point. 48. What is feedback? What is DC feedback and AC feedback? What are positive feedback and negative feedback? A: Feedback is the process of returning a portion of the output to the input. DC feedback affects the Q-point, while AC feedback affects the signal. Positive feedback increases gain, while negative feedback reduces distortion and stabilizes the circuit. 49. Why should we introduce feedback? A: Feedback improves performance by increasing gain, reducing distortion, and improving stability. 50. What are the four configurations of AC negative feedback? A: Current series, current parallel, voltage series, and voltage parallel. 51. What is the general expression of the AC negative feedback amplifier circuit? A: The closed-loop gain is given by A/(1 + βA), where A is the open-loop gain and β is the feedback factor. 52. What effect will it have on performance after introducing current series negative feedback in the amplifier circuit? A: It reduces gain, increases input resistance, and decreases output resistance. 53. What effect will it have on performance after introducing voltage series negative feedback in the amplifier circuit? A: It reduces gain, increases input resistance, and decreases output resistance. 54. What effect will it have on performance after introducing current parallel and negative feedback in the amplifier circuit? A: It reduces gain, decreases input resistance, and increases output resistance. 55. What is the impact on performance after introducing voltage parallel negative feedback in the amplifier circuit? A: It reduces gain, lowers input resistance, and decreases output resistance. 56. What is deep negative feedback? How to estimate the magnification under deep negative feedback? A: Deep negative feedback occurs when the loop gain is much greater than 1. The closed-loop gain is approximately 1/β. 57. The deeper the negative feedback, the better? What is self-oscillation? What kind of feedback amplifier circuit is prone to self-oscillation? How to eliminate self-oscillation? A: No, too much feedback can cause oscillation. Self-oscillation occurs when the phase shift reaches 180°. It can be eliminated by adding compensation capacitors or adjusting the frequency response. 58. Can only introduce negative feedback in the amplifier circuit? Does the amplifier circuit introduce positive feedback to improve performance? A: No, positive feedback can be used to increase input resistance or enhance certain characteristics, such as in bootstrap circuits. 59. What is the configuration of the voltage follower? Can it amplify the input voltage signal? A: A voltage follower is a voltage series feedback circuit. It does not amplify the input voltage but follows it closely. 60. What type of feedback amplifier does the voltage follower belong to? A: It is a voltage series feedback amplifier. 61. Where is the main purpose of the voltage follower? A: It is used to buffer signals between stages, ensuring that the input and output impedances match. 62. What are the input and output characteristics of the voltage follower? A: It has high input resistance and low output resistance. 63. Generally speaking, power amplifiers are divided into several categories? A: They are classified based on conduction angle (Class A, B, AB, C, D) and circuit structure (transformer-coupled, OTL, OCL, BTL). 64. What are the characteristics of Class A and Class B power amplifiers? A: Class A amplifiers have low distortion but high power consumption. Class B amplifiers are more efficient but have higher distortion. 65. Why does Class B power amplifier generate crossover distortion? How to overcome it? A: Crossover distortion occurs due to the dead zone between transistors. It can be reduced by biasing the transistors slightly into conduction. 66. Why do you have to consider power supply, tube consumption, and efficiency when designing a power amplifier? A: These factors determine the maximum power output and overall efficiency of the amplifier. 67. From the perspective of signal feedback, what type of circuit does the oscillator belong to? A: An oscillator is a positive feedback amplifier. 68. What is the starting condition for generating sine wave oscillation? A: The loop gain must be greater than or equal to 1, and the phase shift must be zero. 69. How to form a sine wave oscillation circuit? What parts must it include? A: It requires an amplifier, a frequency-selective network, a positive feedback network, and a stabilization mechanism. 70. How to judge whether the circuit can start up in the sine wave oscillator with transformer coupling? A: Use the instantaneous polarity method to check for positive feedback. 71. How to judge whether the circuit can start up in the three-point sine wave oscillator? A: Check if the feedback is in phase with the input signal. 72. What is the frequency characteristic (or frequency response) of the amplifier circuit? A: It refers to how the gain of the amplifier varies with frequency. 73. Classification of frequency characteristics. A: Frequency characteristics are categorized into amplitude and phase responses. 74. What is the amplitude-frequency characteristic? A: It describes how the magnitude of the gain changes with frequency. 75. What is the phase frequency characteristic? A: It describes how the phase shift between input and output signals changes with frequency. 76. What is Potter? A: A Bode plot is a logarithmic representation of frequency response. 77. Why use Bode plot to represent frequency characteristics? A: Bode plots make it easier to visualize wide ranges of frequencies and gains. 78. What is the upper cutoff frequency of the amplifier circuit? A: It is the frequency at which the gain drops to 0.707 times the mid-band value. 79. What is the lower cutoff frequency of the amplifier circuit? A: It is the frequency at which the gain also drops to 0.707 times the mid-band value. 80. What is a half power point? A: It is the frequency where the output power is half of the maximum, corresponding to a -3dB drop in gain. 81. What is the passband of the amplifier circuit? A: It is the range of frequencies between the lower and upper cutoff frequencies. 82. What is the hazard of the frequency characteristics of the amplifier circuit? A: Poor frequency response can cause waveform distortion, including amplitude and phase distortion. 83. What are the factors that affect the frequency characteristics of the low-frequency amplifier circuit? A: Number of stages, feedback, and coupling capacitors all influence the frequency response. 84. What are the characteristics of the high-frequency circuit frequency characteristics? A: High-frequency circuits may show a decrease in gain and a leading phase shift. 85. What are the characteristics of the low-pass circuit frequency characteristics? A: Low-pass circuits attenuate high frequencies and produce a lagging phase shift. 86. For the amplifying circuit, is the wider the passband, the better? A: Yes, a wider passband allows for more accurate reproduction of complex signals. 87. What is a power amplifier circuit? A: A power amplifier delivers enough power to drive a load, typically located at the final stage of an amplifier. 88. What are the requirements for the main technical performance of the power amplifier circuit? A: It should have high output power, high efficiency, low distortion, and reliable operation. 89. What method is used to analyze the power amplifier circuit? A: Large signal models or graphical methods are commonly used. 90. What is the Class A working state of the triode? A: In Class A, the transistor is conducting throughout the entire signal cycle. 91. What is the Class B working condition of the triode? A: In Class B, the transistor conducts for only half of the signal cycle. 92. What is the working condition of Class A and Class B of the triode? A: Class AB operates between Class A and Class B, conducting for more than half a cycle. 93. What is a transformer coupled power amplifier circuit? A: It uses transformers for coupling between stages, allowing impedance matching. 94. What are the advantages and disadvantages of the transformer-coupled power amplifier circuit? A: It offers good impedance matching but is bulky and has poor frequency response. 95. What is an OCL circuit? A: OCL stands for Output Coupling Less, meaning no output capacitor is used. 96. What are the advantages and disadvantages of OCL circuits? A: It is compact and has good frequency response, but requires dual power supplies. 97. What is an OTL circuit? A: OTL stands for Output Transformer Less, meaning no output transformer is used. 98. What are the advantages and disadvantages of the OTL circuit? A: It needs only one power supply, but has poor low-frequency response. 99. What is a BTL circuit? A: BTL is a bridge push-pull amplifier that uses a single power supply without a transformer or capacitor. 100. What are the advantages and disadvantages of the BTL circuit? A: It has high output power and no need for transformers or capacitors, but uses more transistors and has lower efficiency.
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