"Electronic Technology Foundation" is an important technical basic course for electronics majors. The analog circuit is a course that is difficult for students to learn and difficult for teachers to teach. Amplifier is the basic foundation for analog circuits, and it is also the focus and difficulty of "Electronic Technology Foundation". Only by solving this problem can we enter the field of electronic technology. Through teaching practice, the author gradually formed the main contradiction between nonlinear devices, linear devices and linear amplification, with linear nonlinear linearity as the main line, and analysis and ideas of amplifiers with DC analysis and AC analysis as the main content. It solved the transition from "Circuit" to "Electronic Technology" and solved the problem of difficult entry of electronic technology.
1 from linear to nonlinear
An electronic circuit is a branch of a circuit that is a circuit that contains electronic components, and the electronic device is a nonlinear device, so the electronic circuit is a nonlinear circuit. "Circuit" generally includes a chapter on nonlinear circuits, but the content is small, but it is simply introduced, and it has not attracted enough attention from students. Therefore, the beginning of the "Electronic Technology Foundation" class should start from the linear circuit to the nonlinear circuit.
The "Electronic Technology Foundation" begins with a PN junction, which is the basis of semiconductor devices. After discussing the working principle of the PN junction and obtaining the volt-ampere characteristics of the PN junction, it enters the nonlinearity: its volt-ampere characteristic curve is a nonlinear function. First, we must give the definition of linear resistance, and draw the concept of DC (static) resistance and AC (dynamic) resistance. Compare the linear resistance (the volt-ampere characteristic curve is a straight line passing through the origin, and its DC resistance and AC resistance are equal and A constant) can lead to the following important conclusions:
(1) The direct current resistance and the alternating current resistance of the nonlinear element at any point on the volt-ampere characteristic curve are generally not equal.
(2) The DC resistance and AC resistance of the nonlinear component are not constant, but vary with the static operating point.
The forward resistance of the PN junction is small, and the reverse resistance is large. Therefore, his nonlinearity is often summarized as unidirectional conductivity. The diode is a PN junction. The triode is composed of two PN junctions. When it is in the amplified state, the input characteristics are equivalent to the forward characteristics of the PN junction, and the output characteristics are equivalent to the PN junction of the base region injected under minority carrier control. Reverse characteristics.
The above is the nonlinearity of the electronic device. With the nonlinear characteristics of the electronic device, the difference between the electronic circuit and the general linear circuit can be understood, and the working principle of the amplifier, the setting of the static working point, and the difference between the DC analysis and the AC analysis can be understood.
2 Characteristics of the amplified line brought by nonlinearity
Nonlinear components tend to generate new frequency components, which are nonlinear distortions. This is the primary issue that must be considered in electronic circuits. If the AC signal is directly applied to the emitter junction of the transistor (ie, no static bias is applied), the unidirectional conductivity of the emitter junction can be severe even if the nonlinearity of its dead-band voltage and forward characteristics is neglected. The nonlinear distortion is such that only the positive half cycle is turned on, and the negative half cycle is cut off (the class B working state). Only when the center position of the AC signal is translated along the voltage axis, that is, the forward junction is applied to the emitter junction, and the forward bias value is greater than the amplitude value of the AC signal, so that the PN junction can be positive and negative half of the AC signal. All are turned on (Class A working state), in order to get undistorted amplification, which leads to two conclusions:
(1) In order to overcome the nonlinear distortion caused by the unidirectional conductivity of the PN junction, the amplifier must add a DC bias signal before adding the AC signal.
(2) There are both DC signals and AC signals in the amplifier circuit; the flow loops of the two signals may be different, that is, there are both DC and AC paths; the voltage and current in the amplifier have both DC components and The AC component, ie the instantaneous amount is equal to the DC amount plus the AC amount, which determines the analysis of the amplifier including DC analysis and AC analysis. The DC analysis is to determine the DC operating point of the amplifier. The AC analysis is to calculate the amplification factor, the input and output resistance. Performance indicators such as output power and efficiency as well as frequency response. The path of the DC signal is different from that of the AC signal. In particular, the nonlinear device exhibits different performances for DC signals and AC signals (DC resistance and AC resistance), so DC analysis and AC analysis use different circuit networks and parameters. These are often ignored by some students and should be particularly focused.
3 Linear equivalent circuit analysis of micro-variable signals
In the analysis method of the micro-variation signal in the amplifier, it becomes the analysis problem of the linear circuit, thus completing the whole process of linear---linear---linearity. But this is not going back to the original place, but a qualitative leap and improvement. Although the AC analysis of the amplified line is also a linear analysis, the AC parameters of the nonlinear device at a given quiescent operating point must be used. The nonlinear characteristics still play a role here. In many electronic circuits, the DC of the electronic device is utilized. The resistance and the AC resistance are different. Use this concept to understand and explain how many circuits work. For example, an active load uses this feature to obtain a large AC equivalent resistance in the case of a lower DC supply voltage or a larger quiescent operating current. In the differential amplifier circuit, the long tail is passed. The analysis of the emitter resistance function of the differential amplifier knows that he can effectively reduce the common mode amplification without any influence on the differential mode signal, so the bigger he is, the better. If a linear resistor is used, it is selected under a certain operating current. Large resistors must be limited by the emitter DC supply voltage. This makes it natural to use an active load with a large AC resistance and a small DC resistance.
4 Conclusion
In the circuit circuit course, the general linear circuit analysis, to the nonlinearity of the electronic device, to the linear analysis of the AC signal in the amplified circuit, the task of analyzing the amplified circuit is basically completed, because the circuit is composed of circuit components. The circuit, the analysis circuit is to replace the components with the model of the circuit component, and use the basic law of the circuit and the basic analysis method to solve the network composed of the model of the circuit component. The only difference between the electronic circuit and the general circuit is that it contains the electron. Device. Now, when the electronic device is replaced by his circuit model, the electronic circuit becomes a general circuit, and the analysis becomes an analysis of the general circuit. In this way, it is for the students to understand that the electronic circuit is a circuit. A branch of Electronic Technology is the continuation and extension of Circuits. The basic laws and analysis methods are the same, thus establishing a unified and complete concept of circuit analysis.
1 from linear to nonlinear
An electronic circuit is a branch of a circuit that is a circuit that contains electronic components, and the electronic device is a nonlinear device, so the electronic circuit is a nonlinear circuit. "Circuit" generally includes a chapter on nonlinear circuits, but the content is small, but it is simply introduced, and it has not attracted enough attention from students. Therefore, the beginning of the "Electronic Technology Foundation" class should start from the linear circuit to the nonlinear circuit.
The "Electronic Technology Foundation" begins with a PN junction, which is the basis of semiconductor devices. After discussing the working principle of the PN junction and obtaining the volt-ampere characteristics of the PN junction, it enters the nonlinearity: its volt-ampere characteristic curve is a nonlinear function. First, we must give the definition of linear resistance, and draw the concept of DC (static) resistance and AC (dynamic) resistance. Compare the linear resistance (the volt-ampere characteristic curve is a straight line passing through the origin, and its DC resistance and AC resistance are equal and A constant) can lead to the following important conclusions:
(1) The direct current resistance and the alternating current resistance of the nonlinear element at any point on the volt-ampere characteristic curve are generally not equal.
(2) The DC resistance and AC resistance of the nonlinear component are not constant, but vary with the static operating point.
The forward resistance of the PN junction is small, and the reverse resistance is large. Therefore, his nonlinearity is often summarized as unidirectional conductivity. The diode is a PN junction. The triode is composed of two PN junctions. When it is in the amplified state, the input characteristics are equivalent to the forward characteristics of the PN junction, and the output characteristics are equivalent to the PN junction of the base region injected under minority carrier control. Reverse characteristics.
The above is the nonlinearity of the electronic device. With the nonlinear characteristics of the electronic device, the difference between the electronic circuit and the general linear circuit can be understood, and the working principle of the amplifier, the setting of the static working point, and the difference between the DC analysis and the AC analysis can be understood.
2 Characteristics of the amplified line brought by nonlinearity
Nonlinear components tend to generate new frequency components, which are nonlinear distortions. This is the primary issue that must be considered in electronic circuits. If the AC signal is directly applied to the emitter junction of the transistor (ie, no static bias is applied), the unidirectional conductivity of the emitter junction can be severe even if the nonlinearity of its dead-band voltage and forward characteristics is neglected. The nonlinear distortion is such that only the positive half cycle is turned on, and the negative half cycle is cut off (the class B working state). Only when the center position of the AC signal is translated along the voltage axis, that is, the forward junction is applied to the emitter junction, and the forward bias value is greater than the amplitude value of the AC signal, so that the PN junction can be positive and negative half of the AC signal. All are turned on (Class A working state), in order to get undistorted amplification, which leads to two conclusions:
(1) In order to overcome the nonlinear distortion caused by the unidirectional conductivity of the PN junction, the amplifier must add a DC bias signal before adding the AC signal.
(2) There are both DC signals and AC signals in the amplifier circuit; the flow loops of the two signals may be different, that is, there are both DC and AC paths; the voltage and current in the amplifier have both DC components and The AC component, ie the instantaneous amount is equal to the DC amount plus the AC amount, which determines the analysis of the amplifier including DC analysis and AC analysis. The DC analysis is to determine the DC operating point of the amplifier. The AC analysis is to calculate the amplification factor, the input and output resistance. Performance indicators such as output power and efficiency as well as frequency response. The path of the DC signal is different from that of the AC signal. In particular, the nonlinear device exhibits different performances for DC signals and AC signals (DC resistance and AC resistance), so DC analysis and AC analysis use different circuit networks and parameters. These are often ignored by some students and should be particularly focused.
3 Linear equivalent circuit analysis of micro-variable signals
In the analysis method of the micro-variation signal in the amplifier, it becomes the analysis problem of the linear circuit, thus completing the whole process of linear---linear---linearity. But this is not going back to the original place, but a qualitative leap and improvement. Although the AC analysis of the amplified line is also a linear analysis, the AC parameters of the nonlinear device at a given quiescent operating point must be used. The nonlinear characteristics still play a role here. In many electronic circuits, the DC of the electronic device is utilized. The resistance and the AC resistance are different. Use this concept to understand and explain how many circuits work. For example, an active load uses this feature to obtain a large AC equivalent resistance in the case of a lower DC supply voltage or a larger quiescent operating current. In the differential amplifier circuit, the long tail is passed. The analysis of the emitter resistance function of the differential amplifier knows that he can effectively reduce the common mode amplification without any influence on the differential mode signal, so the bigger he is, the better. If a linear resistor is used, it is selected under a certain operating current. Large resistors must be limited by the emitter DC supply voltage. This makes it natural to use an active load with a large AC resistance and a small DC resistance.
4 Conclusion
In the circuit circuit course, the general linear circuit analysis, to the nonlinearity of the electronic device, to the linear analysis of the AC signal in the amplified circuit, the task of analyzing the amplified circuit is basically completed, because the circuit is composed of circuit components. The circuit, the analysis circuit is to replace the components with the model of the circuit component, and use the basic law of the circuit and the basic analysis method to solve the network composed of the model of the circuit component. The only difference between the electronic circuit and the general circuit is that it contains the electron. Device. Now, when the electronic device is replaced by his circuit model, the electronic circuit becomes a general circuit, and the analysis becomes an analysis of the general circuit. In this way, it is for the students to understand that the electronic circuit is a circuit. A branch of Electronic Technology is the continuation and extension of Circuits. The basic laws and analysis methods are the same, thus establishing a unified and complete concept of circuit analysis.
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