Analog electronic technology is a technology that must be mastered by students majoring in electrical engineering and automation. This course plays a decisive role in professional training programs. Young children are old and old. Today, we may be at work. You will be exposed to this knowledge. Here are some explanations for the difficulties in analog electronic technology.
First, the amplification circuit foundationAs the basis of this course, as the course is just getting started, there are many concepts, and it is necessary to initially develop analysis and calculation skills. Therefore, it is necessary to slow down the progress and ensure sufficient hours.
Regarding the physical basis of semiconductors, it has been said in the two courses "Physics" and "Chemistry". This course does not have to be repeated, and it can be said from the covalent bond structure of crystals. The PN junction is the key content, and it is required to use the physical concept to explain the unidirectional conductivity of the PN junction, the current distribution and amplification principle of the triode. Focus on the characteristics and main parameters of diodes and transistors.
1. In the three basic configurations of amplifiers (co-spray, common-base, and common), the composition and working principle of the common-emitter and common-collector circuits should be emphasized.
2, the graphical analysis of the amplifier, mainly used to determine the static working point and analyze the dynamic working process, does not require it to calculate the magnification.
3. The micro-variable equivalent circuit analysis method is an important tool for analyzing amplifiers. The derivation of H parameters, the establishment of equivalent circuits, the concept of controlled power supply, etc., should be firmly mastered by students. To enable students to calculate the voltage amplification factor, input resistance and output resistance of the device with the h-parameter equivalent. It is necessary to apply the above analysis tools to a level of proficiency through various teaching links.
4. In the characteristic analysis of the operating point stabilization circuit of the amplifier, the emitter bias circuit is mainly used. But for the collector-base bias circuit, you can simply introduce the physical process of its stable working point, and you can also organize students to learn. As for the use of Miller's theorem to analyze this circuit, it can be introduced in the exercises, or guide students to read. Miller's theorem has certain practical value in the approximate analysis of electronic circuits, not only used here.
In the high-frequency characteristic analysis, the term Miller capacitance is derived due to the Miller effect. In the integral and differential circuits composed of integrated operational amplifiers, Miller's theorem can also be used to explain the expansion and reduction of circuit time constants.
5. After introducing the emitter bias circuit, the constant current source can be taken out by the way. As a circuit component, it is not only common in discrete component circuits, but also more commonly used in analog integrated circuits.
6, for the common collector circuit, in addition to the basic circuit, it is best to introduce the concept of composite bootstrap follower, composite tube, used in power amplifiers and power supplies; the concept of bootstrap is also often used in many practical circuits .
Second, FET amplifierThe FET is a unipolar device. This part can be re-examined with the knot-type FET and its amplifying circuit. The insulated gate tube and its amplifying circuit can be compared with the FET and its amplifying circuit.
The junction field effect transistor is a field effect device based on a PN junction. Be familiar with its simple structure and working principle, characteristic curves, main parameters and points of use.
For FET amplifiers, the main purpose of the bias circuit and its AC amplification (input voltage to output current control) is explained. Due to the dispersion of device characteristics, when analyzing the operating point of the expression, the formula can be biased
Calculation method. When analyzing the index such as its magnification, the micro-variable equivalent circuit method is used.
Third, the frequency characteristics and multi-stage amplifier1. This part of the content, first of all, must clearly study the actual background, purpose, significance of the frequency characteristics of the amplifier, and explain the basic concepts, so that students understand from the physical concept of the DC capacitor and the emitter bypass capacitor to the circuit low frequency
Sexual effects, junction capacitance (general name of diffusion capacitance and barrier capacitance) and the effect of wiring capacitance on the high frequency characteristics of the circuit.
2, for the sake of simplicity, the RC high-pass and RC low-pass circuits can be used to discuss the approximate analysis method of frequency characteristics - Bode plot method. Then, the RC-coupled amplifier is simplified to a high-pass circuit and a low-pass circuit for analysis.
3. When discussing the low-frequency characteristics of the common-emitter circuit, the influence on the low-frequency characteristics can be affected by the output (the emitter bypass capacitor basically has no conversion problem in the output loop, and the emitter bypass capacitor is generally much larger than the output coupling capacitor, so the emission The effect of the pole bypass capacitor on the low-frequency characteristics of the output loop is negligible. The time constant of the input loop is determined. (As for the effect of the emitter bypass capacitor on the low-frequency characteristics, the emitter bypass capacitor can be folded into the base circuit for processing. Determined by the time constant of the input loop), if the lower limit cutoff determined by the input loop and the output loop is more than four times different from each other, the larger one is used as the lower limit frequency of the amplifier.
4. When discussing the high-frequency characteristics of the circuit, focus on the high-frequency parameters of the hybrid ç‰æ•ˆ-type equivalent circuit and the triode.
5. The transient characteristics of a single-stage amplifier may not be required.
6. The RC-coupled multi-stage amplifier mainly calculates its voltage amplification factor. In the calculation process, it is necessary to pay attention to the mutual influence between the stages. It is necessary for the students to grasp an important relationship, that is, the output resistance of the pre-stage is the internal resistance of the post-stage signal source. The input resistance of the latter stage is the load of the previous stage. For the frequency response of the multi-stage amplifier, it is possible to qualitatively understand that the more the number of stages, the narrower the frequency band is.
Fourth, feedback amplifier and sine wave oscillatorFeedback is the focus and difficulty of electronic technology.
1. First, establish the concept of feedback through the emitter bias amplification circuit (in fact, when the working point is stabilized in Chapter 1, the concept of feedback is introduced), and then abstract from this special case into a general block diagram.
This leads to the general expression of the magnification. The instantaneous polarity method can be used to distinguish between positive and negative feedback and four types of feedback circuits and their characteristics, which can explain the influence of negative feedback on the performance of the amplifier.
2. Due to the fact that the negative feedback amplifier usually satisfies the deep negative feedback condition in the engineering practice, the quantitative analysis of the amplification factor of the negative feedback amplifier is mainly based on the approximate estimation under the condition of deep negative feedback.
3, the block diagram analysis method of the negative feedback amplifier, generally as a deepening and widening content, this part can not be said.
4. Regarding the stability problem of the negative feedback amplifier, we first introduce the cause of self-excitation, the condition of self-oscillation, and then introduce the method of eliminating self-excited oscillation with a qualitative concept. For example, the inter-stage base-to-ground of the amplifier or the small capacitor C or the RC series circuit is connected between the collector and the base of the triode, which is mainly explained by the destruction of the oscillation condition. This part of the content can also be treated as self-study.
5, sine wave oscillator to clarify the principle of generating oscillation, focusing on the phase balance and amplitude balance conditions of the oscillator. For RC and LC oscillators, an alternative (such as RC bridge circuit) is the focus, and other types can be described briefly. This part mainly requires students to understand the composition of the circuit, master the method of correctly judging positive feedback and the calculation of the oscillation frequency.
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