Why can't a single-tube amplifier circuit meet the requirements of multiple performance aspects?

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Why can't a single-tube amplifier circuit meet the requirements of multiple performance aspects? [Copy link]

Answer: The amplification capacity is limited; the input and output resistances cannot simultaneously take into account the good matching of the amplifier and the outside world.

41. What is the basic purpose of the coupling circuit?

Answer: Let the useful AC signal pass smoothly between the front and rear amplifiers, and at the same time play a good isolation in static terms.

42. How many ways are there for inter-stage coupling in multi-stage amplifier circuits?

Answer: Generally there are several ways: RC coupling, transformer coupling and direct coupling.

43. What is the total voltage gain of a multi-stage amplifier circuit?

Answer: It is equal to the product of the gains of each stage.

44. What are the input and output resistances of a multi-stage amplifier circuit equal to?

Answer: They are equal to the input resistance of the first stage and the output resistance of the last stage respectively.

45. What are the special problems of direct-coupled amplifier circuits? How to solve them?

Answer: Zero drift is the biggest problem of direct-coupled amplifier circuits. The most fundamental solution is to use a differential amplifier.

46. Why is the three-stage amplifier circuit the most common?

Answer: Too few stages will result in insufficient amplification, while too many stages will make it difficult to solve problems such as zero drift.

47. What is zero drift? What are the main causes of it? What is the most fundamental one?

Answer: When the input signal of the amplifier is zero, its output end still has the phenomenon of slow and irregular output signal. The main reason for this phenomenon is that the parameters of circuit components fluctuate due to the influence of temperature, which leads to the instability of Q point. In multi-stage amplifiers, due to the direct coupling method, the fluctuation of Q point will be transmitted and amplified step by step.

48. What is feedback? What is DC feedback and AC feedback? What is positive feedback and negative feedback?

Answer: The phenomenon that the output signal is sent back to the input end through a certain path and reprocessed by the amplifier is called feedback. If the signal is DC, it is called DC feedback; if it is AC, it is called AC feedback. After reprocessing, if the final output of the amplifier is larger than before the introduction of feedback, it is called positive feedback. On the contrary, if the final output of the amplifier is smaller than before the introduction of feedback, it is called negative feedback.

49. Why do we need to introduce feedback?

Answer: Generally speaking, it is to improve the performance of the amplifier. The introduction of positive feedback is to enhance the amplifier's sensitivity to weak signals or increase the gain; while the introduction of negative feedback is to improve the amplifier's gain stability and operating point stability, reduce distortion, improve input and output resistance, widen the passband, and so on.

[p=24, null, leftleft]50. What are the four configurations of AC negative feedback?

Answer: They are current series, current parallel, voltage series and voltage parallel.

51. What is the general expression of an AC negative feedback amplifier circuit?

Answer: .

52. What effect will the introduction of current series negative feedback have on the performance of the amplifier circuit?

Answer: It will weaken the voltage gain, improve its gain stability, reduce distortion, increase input resistance, and increase output resistance.

53. What effect will the introduction of voltage series negative feedback have on the performance of the amplifier circuit?

Answer: It can weaken the voltage gain, improve its gain stability, reduce distortion, reduce input resistance, and reduce output resistance.

54. What effect will the introduction of current parallel negative feedback have on the performance of the amplifier circuit?

Answer: It can weaken the voltage gain, improve its gain stability, reduce distortion, reduce input resistance, and increase low output resistance.

55. What effect will the introduction of voltage parallel negative feedback have on the performance of the amplifier circuit?

Answer: It can weaken the voltage gain, improve its gain stability, reduce distortion, reduce input resistance, and reduce low output resistance.

56. What is deep negative feedback? Under deep negative feedback conditions, how to estimate the amplification factor?

Answer: In a feedback amplifier, if 1, then the amplifier that meets this condition is called a deep negative feedback amplifier. At this time, the closed-loop gain of the amplifier is completely determined by the feedback coefficient.

null, left]54. What effect will the introduction of current parallel negative feedback have on the performance of the amplifier circuit?