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1. Is a hole a kind of carrier? Does the hole move electrons when it conducts electricity?
A: No, but in its movement it can be equivalent to a carrier. When the hole is conductive, the electrons of the same amount move in the opposite direction.
2. What ratio is generally doped in the intrinsic semiconductor when preparing an impurity semiconductor?
A: Incorporate in a ratio of one-millionth.
3. What is an N-type semiconductor? What is a P-type semiconductor? What happens when two semiconductors are fabricated together?
A: Most semiconductors whose carriers are free electrons are called N-type semiconductors. Conversely, a semiconductor in which most carriers are holes is called a P-type semiconductor. When the P-type semiconductor is bonded to the N-type semiconductor, a PN junction is formed.
4. What are the main physical characteristics of the PN junction?
A: Unidirectional conductivity and more sensitive temperature characteristics.
5. What are the characteristics of semiconductor device manufacturing electronic devices compared with traditional vacuum electronic devices?
Answer: The frequency characteristics are good, the volume is small, the power consumption is small, and the integrated products of the circuit are easy to be pocketed. In addition, it is particularly prominent in terms of strong seismic resistance and reliability; however, it is inferior to vacuum devices in terms of distortion and stability.
6. What are intrinsic semiconductors and impurity semiconductors?
A: Pure semiconductors are intrinsic semiconductors, and they are generally medium-priced elements in the periodic table. An impurity semiconductor is obtained by incorporating a high monovalent or low monovalent impurity element in an intrinsic semiconductor in a very small ratio.
7. What are the names of PN knots?
A: Space charge zone, barrier layer, depletion layer, etc.
8. Is the voltage and current applied to the PN junction linear? Why does it have unidirectional conductivity?
Answer: It is not linear. When the forward voltage is applied, the holes in the P region and the electrons in the N region attract each other under the electric field established by the forward voltage to produce a composite phenomenon, resulting in a thinning of the barrier layer and a forward current with voltage. The growth grows exponentially, and the conduction state is macroscopically. When the reverse voltage is applied, the situation is opposite to the above. The barrier layer becomes thicker, the current is almost completely zero, and the cutoff state is macroscopically. This is the unidirectional conduction characteristic of the PN junction.
9. Is there really no current when the reverse voltage is applied to the PN junction?
A: There is no current at all, and minority carriers generate very little reverse leakage current under the action of reverse voltage.
10. What are the most basic technical parameters of a diode?
A: Maximum rectified current
11. What are the main uses of diodes?
Answer: Rectification, detection, voltage regulation, etc.
12. How does the transistor control the collector current?
A: Through the current distribution relationship.
13. Can I use two diodes to reverse each other to form a triode? Why?
Answer: No; the two diodes are connected to each other through the metal electrode, and there is no base area required for the triode.
14. What is the penetration current of the triode? What effect does it have on the amplifier?
Answer: When the base is open, the current between the collector and the emitter is the through current: where is the collector-base reverse leakage current, and both are generated by the movement of minority carriers, so The temperature is very sensitive and both will increase dramatically as the temperature rises. This has an adverse effect on the amplifier. Therefore, in actual work, they are required to be as small as possible.
15. What is the gate voltage of the triode?
A: The silicon tube is generally 0.5 volts. The bismuth tube is about 0.2 volts.
16. Does the amplification circuit amplify the electrical signal and the magnifying glass amplifies the object with the same meaning?
A: Not the same.
17. What are the basic bias conditions in an amplifier consisting of a triode?
Answer: The emitter junction is positively biased; the collector junction is reverse biased.
18, triode input and output characteristic curve is generally divided into several areas?
A: Generally divided into enlarged area, saturated area and cut-off area.
19. What are the basic configurations of the amplifier circuit? What are they?
Answer: Three types are common emitter, common base and common collector.
20. In the common emitter amplifying circuit, what kinds of bias circuits are generally available?
A: There are upper base, partial pressure and set-base feedback.
21. What is the significance of the determination of the static working point for the amplifier?
A: Correctly determining the quiescent operating point allows the amplifier to have minimal cut-off distortion and saturation distortion, while also achieving maximum dynamic range and improved efficiency of the triode.
22. What is the static working point of the amplifier that should normally be in the input and output characteristic curve of the triode?
A: It should normally be in the center of the amplification area of ​​the triode input and output characteristic curve.
23. Should I treat the power supply and capacitors when drawing the DC path of the amplifier?
A: The capacitor should be considered an open circuit and the power supply is considered an ideal power source.
24. Which amplifiers are suitable for the diagram of the amplifier?
Answer: It is generally suitable for common-emitter base-based single-tube 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 determines the DC path parameters when it is static. The meaning of the AC load line is to analyze the maximum effective amplitude and waveform distortion of the amplifier output when there is an AC signal.
26. How to evaluate the performance of the amplifier circuit? What are the main indicators?
Answer: The performance of the amplifier circuit is generally determined by the following indicators: gain, input and output resistance, passband, 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?
Answer: The unit of voltage gain of the amplifier is often used in decibels: (1) The value becomes smaller and the reading and writing is convenient. (2) Convenient operation. (3) It is in line with the sense of hearing and is easy to estimate. The relationship between the two is:
28. Is the passband of the amplifier as wide as possible? Why?
A: No! The width of the amplifier passband is not as wide as possible. The key is to see if the amplifier has any special requirements on the frequency of the signal being processed! For example, the frequency-selective amplifier requires a narrow passband, and the general audio amplifier The passband is wider.
29. What is the effect of the amplifier's input and output resistance on the amplifier?
A: The higher the input resistance of the amplifier should be, the better the output of the input source can be, and the effective signal consumed by the internal resistance of the source can be reduced to a minimum. The output resistance should be as low as possible, which increases the effective output signal ratio on the load.
30. When designing an amplifier, what is the value principle for the input and output resistors?
A: High in and out.
31, the distortion of the amplifier is generally divided into several categories?
Answer: Single-tube AC ​​small-signal amplifiers generally have three types of saturation distortion, cut-off distortion and nonlinear distortion. Push-pull power amplifiers may also have crossover distortion.
32. What kind of distortion will the amplifier's working point be too high? Is the working point too low?
A: saturation distortion, cutoff distortion
33. What are the causes of nonlinear distortion of the amplifier?
A: The working point falls in the nonlinear region of the input characteristic curve, and the minimum value of the input signal is not zero, which causes nonlinear distortion.
34. What is the difference between the micro-variable equivalent circuit analysis method and the graphical method in the analysis of the amplifier?
A: It is convenient and accurate to calculate the input and output resistance, voltage gain, etc. of the amplifier. The graphical rule can more intuitively analyze whether the working point of the amplifier is set properly, whether it will produce distortion and dynamic range.
35. What are the general steps for analyzing the amplifier circuit using the micro-variable equivalent circuit analysis method?
Answer: 1) Calculate the Q point; 2) Calculate the triode according to the formula. 3) Draw the AC path of the amplifier with a micro-variable equivalent circuit. 4) Calculate the input and output resistance, voltage gain, etc. of the amplifier according to 3) and the corresponding formula.
36. What is the scope of application of the micro-variable equivalent circuit analysis method?
A: Suitable for analyzing any simple or complex circuit. As long as the amplifier components therein operate substantially in the linear range.
37. What are the limitations of the micro-variable equivalent circuit analysis method?
A: It can only solve the calculation problem of AC component. It can't be used to determine Q point, nor can it be used to analyze nonlinear distortion and maximum output amplitude.
38. What are the main factors affecting the stability of the working point of the amplifier?
Answer: Temperature drift of component parameters, power supply fluctuations, etc.
39. What method is generally used to stabilize the working point in the common emitter amplifying circuit?
A: Introduce current series negative feedback.
40. Why can't a single-tube amplifier circuit meet the requirements of multi-faceted performance?
A: The amplification capability is limited; in terms of input and output resistance, it is not possible to take into account both the amplifier and the outside world.
41. What is the basic purpose of the coupling circuit?
A: Let the useful AC signal pass smoothly between the front and rear amplifiers, while being well isolated in terms of static.
42. How many ways do inter-stage coupling of multi-stage amplifier circuits?
Answer: There are generally several ways of RC coupling, transformer coupling and direct coupling.
43. What is the total voltage gain of the multistage amplifier circuit?
A: Equal to the product of the gains at each level.
44. What is the input and output resistance of a multi-stage amplifier circuit?
Answer: The input resistance of the first stage is equal to the output resistance of the final stage.
45. What are the special problems of direct coupled amplifier circuits? How to solve them?
A: Zero drift is the biggest problem with direct coupled amplifier circuits. The most fundamental solution is to use a differential amplifier.
46. ​​Why is the amplification circuit the most common in three levels?
A: The number of stages is too small, the amplification ability is insufficient, and too many problems are difficult to solve the zero drift.
47. What is the zero drift? What are the main reasons for this? What is the most fundamental one?
A: When the input signal of the amplifier is zero, the output still has a slow and irregular output signal. The main reason for this phenomenon is that the parameters of the circuit components are fluctuated due to the temperature, which leads to the instability of the Q point. In the multi-stage amplifier, the direct coupling method is adopted, which causes the fluctuation of the Q point to be transmitted and amplified step by step.
48. What is feedback? What is DC feedback and AC feedback? What are positive feedback and negative feedback?
Answer: The phenomenon that the output signal is sent back to the input terminal and reprocessed by the amplifier through a certain way is called feedback. If the signal is DC, it is called DC feedback; if it is AC, it is called AC feedback. After reprocessing, making the final output of the amplifier larger than before introducing feedback is called positive feedback. Otherwise, if the final output of the amplifier is before the feedback is introduced. Smaller, it is called negative feedback.
49. Why should we introduce feedback?
A: In general, to improve the performance of the amplifier, positive feedback is introduced to enhance the sensitivity of the amplifier to weak signals or to increase the gain. Negative feedback is introduced to improve the gain stability of the amplifier and the stability and reduction of the operating point. Small distortion, improved input and output resistance, widened passband, and more.
50. What are the four configurations of AC negative feedback?
Answer: There are four configurations of current series, current parallel, voltage series, and voltage parallel.
51. What is the general expression of the AC negative feedback amplifier circuit?
answer: .
52. What effect will it have on performance after introducing current series negative feedback in the amplifier circuit?
A: It has a weakening effect on voltage gain, improving its gain stability, reducing distortion, increasing input resistance, and improving output resistance.
53. What effect will it have on performance after introducing voltage series negative feedback in the amplifier circuit?
A: It has a weakening effect on voltage gain, can improve its gain stability, reduce distortion, reduce input resistance, and reduce output resistance.
54. What effect will it have on performance after introducing current parallel and negative feedback in the amplifier circuit?
A: It has a weakening effect on voltage gain, can improve its gain stability, reduce distortion, reduce input resistance, and improve low output resistance.
55. What is the impact on performance after introducing voltage parallel negative feedback in the amplifier circuit?
A: It has a weakening effect on voltage gain, can improve its gain stability, reduce distortion, reduce input resistance, and reduce low output resistance.
56. What is deep negative feedback? How to estimate the magnification under deep negative feedback?
A: In the feedback amplifier, such as medium-1, the amplifier that satisfies this condition is called the deep negative feedback amplifier. The closed-loop gain of the amplifier at this time is completely determined by the feedback coefficient.
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. When the closed-loop gain of the negative feedback amplifier circuit is =0, it means that the circuit has an output when the input amount is 0, and the circuit is said to have self-oscillation. When the signal frequency enters the low frequency or high frequency band, the negative feedback amplifying circuit is prone to self-oscillation due to the generation of the additional phase shift. To eliminate self-oscillation, it is necessary to destroy the conditions that generate oscillations and change the frequency characteristics of AF.
58. Can only introduce negative feedback in the amplifier circuit? Does the amplifier circuit introduce positive feedback to improve performance?
A: No. Energy, such as the bootstrap circuit, introduces appropriate positive feedback to introduce input feedback to increase the input resistance.
59. What is the configuration of the voltage follower? Can it amplify the input voltage signal?
A: The voltage follower is a voltage series amplifier. It cannot amplify the input voltage signal.
60. What type of feedback amplifier does the voltage follower belong to?
A: The voltage follower is a voltage series feedback amplifier.
61. Where is the main purpose of the voltage follower?
Answer: The main purpose of voltage follower: generally used in the input stage and output stage of multi-stage amplifier circuit, it can also connect two circuits to play the buffering role.
62. What is the input and output characteristics of the voltage follower?
Answer: The input and output characteristics of the voltage follower: high input resistance and low output resistance.
63. Generally speaking, power amplifiers are divided into several categories?
Answer: According to the difference of the conduction angle of the transistor in the whole cycle, it can be divided into Class A, Class B, Class A, Class C, and Class D. According to different circuit structure, it can be divided into transformer coupling, no output transformer OTL, no output capacitor OCL, bridge push-pull power amplifier circuit BTL.
64. What are the characteristics of Class A and Class B power amplifiers?
Answer: The characteristics of Class A power amplifier: The transistor is turned on during the whole period of the signal, and the power consumption is large and the distortion is small. The characteristics of the class B power amplifier are: the transistor is turned on only in the half cycle of the signal, and the power consumption is small. The distortion is large.
65. Why does Class B power amplifier generate crossover distortion? How to overcome it?
A: Because the turn-on voltage between the transistors be Uon, when the input voltage value |ui|[ u]
66. Why do you have to consider power supply, tube consumption, and efficiency when designing a power amplifier?
Answer: Because the power amplifier circuit outputs the power as much as possible when the power supply voltage is determined.
67. From the perspective of signal feedback, what type of circuit does the oscillator belong to?
A: From the perspective of signal feedback, the oscillator is a positive feedback amplifier circuit.
68. What is the starting condition for generating sine wave oscillation?
A: The starting condition for generating sinusoidal oscillation is.
69. How to form a sine wave oscillation circuit? What parts must it include?
Answer: The composition of the sine wave circuit: amplifying circuit, frequency selective network, positive feedback network, and stable link.
70. How to judge whether the circuit can start up in the sine wave oscillator with transformer coupling?
Answer: A method for judging whether a circuit can start in a transformer-coupled sine wave oscillator: instantaneous polarity method.
71. How to judge whether the circuit can start up in the three-point sine wave oscillator?
Answer: In the three-point sine wave oscillator, it is judged whether the circuit can start to vibrate: the same base is reversed.
72. What is the frequency characteristic (or frequency response) of the amplifier circuit?
A: The performance of the amplifying circuit (which mainly refers to the voltage amplification factor Au) to the sinusoidal input of different frequencies is called the frequency characteristic of the amplifying circuit.
73. Classification of frequency characteristics.
A: The frequency characteristics are divided into amplitude frequency characteristics and phase frequency characteristics.
74. What is the amplitude-frequency characteristic?
A: The amplitude-frequency characteristic refers to the characteristic of the magnitude of the amplification (ie, the ratio of the amplitude of the input and output sinusoidal voltages) as a function of frequency.
75. What is the phase frequency characteristic?
Answer: The phase-frequency characteristic refers to the phase difference between the output voltage and the input voltage (that is, the phase shift of the amplifier circuit to the signal voltage) as a function of frequency.
76. What is Potter?
A: When the frequency characteristic curve adopts logarithmic coordinates, it is called Bode plot.
77. Why use Bode plot to represent frequency characteristics?
A: Because the frequency response of the input signal is often set in the range of a few Hz to millions of megahertz when studying the frequency response of the amplifying circuit; the amplification factor of the amplifying circuit can be several times to several million times; in order to be in the same coordinate system Represents such a wide range of variation, so logarithmic coordinates, ie Bode plots, are used.
78. What is the upper cutoff frequency of the amplifier circuit?
A: The signal frequency rises to a certain extent, and the value of the amplification factor will also decrease, so that the amplification factor value is equal to 0.707 times | The frequency of Am| is called the upper limit cutoff frequency fH.
79. What is the lower cutoff frequency of the amplifier circuit?
A: The signal frequency drops to a certain extent, and the magnification value will also decrease, so that the amplification factor is equal to 0.707 times |Am| is called the lower cutoff frequency fL.
80. What is a half power point?
Answer: When the signal frequency is the upper limit cutoff frequency fH or the lower limit cutoff frequency fL, the output voltage amplification factor |Am| drops to 0.707 times |Am|, that is, the corresponding output power also drops to half of the amplitude, so fH or fL also Called a half power point.
81. What is the passband of the amplifier circuit?
A: The frequency band formed between fH and fL is called the passband BW of the amplifier circuit and can be expressed as BW = fH-fL.
82. What is the hazard of the frequency characteristics of the amplifier circuit?
A: If the frequency characteristic of the amplifier circuit is not good, when the input signal is non-sinusoidal, the output signal waveform will be different from the input waveform, that is, the waveform distortion will be generated. This distortion is called frequency distortion. The frequency distortion caused by the difference in the amplitude-frequency characteristics, that is, the magnitude of the different frequency amplification factors, is called amplitude distortion; because the phase-frequency characteristic is not good, that is, the phase distortion is not proportional to the frequency, and the frequency distortion is called phase distortion. .
83. What are the factors that affect the frequency characteristics of the low-frequency amplifier circuit?
Answer: The frequency characteristics of the low-frequency amplifier circuit are mainly affected by the following factors: (1) The more the number of stages of the amplifier circuit, the narrower the passband and the worse the frequency characteristics. (2) Introducing negative feedback in the circuit, which can broaden the passband and improve the frequency characteristics. (3) The coupling capacitor, the output resistance of the preamplifier circuit, and the input resistance of the post amplifier circuit also have an effect on the frequency characteristics.
84. What are the characteristics of the high-frequency circuit frequency characteristics?
A: The Qualcomm circuit drops in the low-frequency amplification factor and produces a leading phase shift.
85. What are the characteristics of the low-pass circuit frequency characteristics?
Answer: The low-pass circuit decreases in the high-frequency amplification factor and produces a lagging phase shift.
86. For the amplifying circuit, is the wider the passband, the better?
A: For the amplifier circuit, the wider the passband, the better.
87. What is a power amplifier circuit?
A: A power amplifier circuit is an amplifier circuit that can output enough power to drive the load. Because it is generally located at the last stage of a multi-stage amplifier circuit, it is often referred to as a final stage amplifier circuit.
88. What are the requirements for the main technical performance of the power amplifier circuit?
Answer: The power amplifier circuit is a large signal amplifier circuit. The main technical performance requirements are: (1) the output power should be large enough; (2) the conversion efficiency should be high; (3) the power consumption of the triode should be small; (4) the nonlinear distortion should be small; (5) the work of the triode Be safe and reliable.
89. What method is used to analyze the power amplifier circuit?
Answer: Since the power amplifier circuit works under large signal conditions, it is not suitable to use the small signal equivalent circuit analysis method. It is usually analyzed by large signal model or graphic method. The most used method is the graphic method.
90. What is the Class A working state of the triode?
Answer: In the amplifying circuit, when the input signal is sinusoidal, if the triode is conducting during the entire period of the signal (ie, the conduction angle θ=360°), it is said to work in the class A state.
91. What is the Class B working condition of the triode?
Answer: In the amplifying circuit, when the input signal is a sine wave, if the transistor is only turned on in the positive half cycle or the negative half cycle of the signal (ie, the conduction angle θ=180°), it is said to work in the class B state.
92. What is the working condition of Class A and Class B of the triode?
Answer: In the amplifying circuit, when the input signal is sinusoidal, if the conduction time of the triode is greater than half a cycle and less than the period (ie, the conduction angle θ=180°~360°), it is said to work in A and B. Class status.
93. What is a transformer coupled power amplifier circuit?
Answer: The power amplifier circuit with both input coupling transformer and output coupling transformer is called transformer coupled power amplifier circuit.
94. What are the advantages and disadvantages of the transformer-coupled power amplifier circuit?
Answer: The advantage of transformer-coupled power amplifier circuit is that impedance transformation can be realized. The disadvantage is that it is bulky, bulky, consumes non-ferrous metals, and has low frequency, and low frequency and high frequency characteristics are poor.
95. What is an OCL circuit?
Answer: OCL circuit refers to the power amplifier circuit without output coupling capacitor.
96, What are the advantages and disadvantages of OCL circuits?
Answer: The OCL circuit has the advantages of small size, light weight, low cost and good frequency characteristics. But it requires two sets of symmetric positive and negative power supplies, which is not convenient enough in many cases. 97. What is an OTL circuit? A: The OTL circuit is a power amplifier circuit that does not have an output coupling transformer.
98. What are the advantages and disadvantages of the OTL circuit?
A: The advantage of the OTL circuit is that only one set of power supplies is required. The disadvantage is that it needs to be able to turn a group of power supplies into two sets of symmetrical positive and negative power supplies; the low frequency characteristics are poor.
99. What is a BTL circuit? A: In order to achieve single-supply power supply, and without a transformer and a large capacitor, a bridge push-pull power amplifier circuit, referred to as a BTL circuit, can be used.
100. What are the advantages and disadvantages of the BTL circuit? A: The advantages of the BTL circuit are that only a single power supply is required, and the transformer and the large capacitor are not required, and the output power is high. The disadvantage is that the number of tubes used is large, it is difficult to achieve ideal symmetry of the tube characteristics, and the total loss of the tube is large, and the conversion efficiency is low.
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