Therefore, it must be pointed out that this course is a technical basic course, focusing on the word "technical". On the basis of qualitative analysis and understanding of concepts, quantitative estimation is carried out. Due to the dispersion of semiconductor device parameters, there are large deviations, and components such as resistors and capacitors generally have errors of more than ±5%, and some are even larger. Therefore, blind pursuit of rigorous calculations is of little significance. Therefore, in this course, special attention should be paid to the training of approximate calculations and methods for dealing with engineering problems. In addition, this course is a more practical course. Therefore, it is necessary to emphasize the importance of the experimental class. It is necessary to closely combine theory with practice and strengthen the cultivation of electronic technology practice ability and experimental research ability.
First, the amplification circuit foundation
As 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 approximation analysis of electronic circuits. It is not only used here in the analysis of high-frequency characteristics, but also derives the term Miller capacitance 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 amplifier
The 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, the formula calculation method can be emphasized when analyzing the operating point of the expression. When analyzing the index such as its magnification, the micro-variable equivalent circuit method is used.
Third, the frequency characteristics and multi-stage amplifier
1. In this part of the content, we must first study the actual background, purpose, significance of the frequency characteristics of the amplifier, and explain the basic concepts, so that students can understand the influence of the DC blocking capacitor and the emitter bypass capacitor on the low-frequency characteristics of the circuit from the physical concept. The effect of the capacitance (the general term for the diffusion capacitance and the barrier capacitance) and the 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.
Line array sound is a speaker system, and its technology and manufacturing have been developing steadily for many years. Recently, the situation has changed, and linear array speaker systems have appeared at many major sports events and large performances in the world.Linear array is a group of radiating elements arranged in a straight line and closely spaced, and has the same amplitude and phase. Through linear transmission, the transmission distance is increased and the attenuation during sound transmission is reduced.The advantages of linear array sound reinforcement systems are obvious.
(1) Due to the characteristics of the linear array, the directivity in the vertical plane of the main axis is a narrow beam, and the energy superposition can be radiated at a long distance. The lower end of the curved part of the linear column covers the near area, forming a coverage from near to far.(2) The improvement of the linear array amplifier is more in line with the requirements of technology, process and installation. The middle high-frequency part is more special, 2 (JBL) or 3 (V) tweeter outlets are connected together fJ2j, JBL company called it a sound wave generator, E-V company called it a plane wave generator. According to the analysis with MAPP software, the directivity of the linear array becomes more and more uniform with the increase of frequency. When a certain frequency is reached, such as 1000Hz, the directivity is radial, that is, the flap appears in the directivity map. At this time, the acoustic waveformer composed of the tweeter comes into play, so that the high-frequency directivity is superimposed. (3) Linear arrays cannot ignore mutual interference, and linear arrays themselves do not improve sound quality.
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