Technical requirements: voltage gain is greater than 100 times (1280), maximum undistorted voltage output amplitude is greater than 1.5v, bandwidth is 30Hz-20kHz, input impedance is greater than 1kω( 1.7kω), and output impedance is less than.
Contents of this project:
First, the coupling mode of multistage amplifier circuit
Direct-coupled amplifier circuit has the problem of temperature drift, but it is widely used because of its good low-frequency characteristics, which can amplify slowly varying signals and facilitate integration.
Resistance-capacitance coupling amplifier circuit uses coupling capacitor to isolate DC and pass AC, but its low frequency characteristics are poor and it is not convenient to integrate, so it is only used when the cost of discrete component circuit is not feasible.
Second, the dynamic parameters of multistage amplifier circuit
The voltage amplification of a multipole amplifier circuit is equal to the product of the voltage amplification of the circuits at all levels that make up it. Its input resistance is the input resistance of the first stage and its output resistance is the output resistance of the last stage. When solving the voltage amplification of a certain stage, the input resistance of the latter stage should be taken as the load.
Firstly, the frequency response describes the adaptability of the amplifier circuit to different frequency signals. The loop where the coupling capacitor and the bypass capacitor are located is a Qualcomm circuit, which reduces the amplification factor of the low frequency band and produces a leading phase shift. The loop where the inter-electrode capacitor is located is a low-pass circuit, which reduces the value of the amplification factor in the high frequency band and produces a lagging phase shift.
Secondly, when studying the frequency response, the high-frequency equivalent model of the amplifier tube should be adopted. In the high-frequency equivalent model of transistor, the capacitance between electrodes is equivalent to C'.
Thirdly, the upper limit frequency and lower limit frequency of the amplifier circuit depend on the time constant of the loop where the capacitor is located. The passband is equal to the difference between high frequency and low frequency.
4. Under some conditions, the gain bandwidth is approximately constant. In order to have high frequency characteristics, we should first choose the lamp with high cutoff frequency, and then choose the parameters reasonably to make the equivalent resistance of C' in the loop as small as possible. In order to have good low frequency characteristics, direct coupling should be adopted.
5. The Porter diagram of multistage amplifier circuit is the algebraic sum of Porter diagrams of all levels considering the interaction between the front and back stages.
The key points are:
High frequency, low frequency and passband. Voltage peak-to-peak, gain bandwidth product.
Design block diagram:
Because the AC voltage source (VSIN) has internal resistance objectively, in order to make full use of the voltage source, the internal resistance should be reduced, so the input resistance should be as large as possible. The resistance value of that output resistor is as small as possible.
Multi-stage amplification circuit frequency should be adopted.
Because low-pass circuit and Qualcomm circuit are involved, inter-electrode capacitance, even sum capacitance and bypass capacitance should be considered in the circuit block diagram design.
Because it involves the static working point, the circuit diagram should have DC power supply (VDC).
Circuit diagram of audio voltage amplifier
The simulation parameters are set as follows
Simulation results:
Voltage at each node
Current of each branch
voltage gain
As shown in the figure, the upper cutoff frequency is 38.3 12K and the lower cutoff frequency is 23.8 15.
So its passband is 38.312k-23.5438+0538.288k.
Output voltage V(7)
Input impedance Ri=2.752k
Analog circuit diagram when calculating output impedance
The voltage of each node after simulation
Current of each branch after simulation
Output impedance R0=967.660
The simulation results show that
Due to the reverse voltage applied to the collector junction, the drift motion of balanced minority carriers forms ICBO, and the thermal motion intensifies when the temperature rises, and the minority carrier concentration increases obviously. Therefore, the number of minority carriers participating in the drift motion increases, which is the increase of ICBO from the outside. Because ICEO=( 1+ )ICBO, the increase of ICBO is less than the simulation value when the temperature rises.
Experience and harvest of curriculum design
This semester, we set up the course Analog Circuit, which belongs to the category of electronic circuits and is closely related to our major, and both of them are theoretical guidance. As the saying goes, "it's too shallow to talk on paper. If you know it, you have to do it." It is not enough to learn anything theoretically without practice and exploration, so at the end of this semester, the teacher arranged an electronic course design for us. Curriculum design is an important link to cultivate students' comprehensive use of the knowledge they have learned to discover, put forward and solve practical problems and exercise their practical ability. This will not only deepen our understanding of electronic circuits, but also timely and truly apply what we have learned.
The intense and hard three-week course design is over. When I was about to finish the task assigned by my teacher, I seemed to have climbed the mountain and climbed the top once. I feel relaxed and refreshed, and my eyes are suddenly enlightened. ...
Looking back on the design of this course, I feel a lot. From theory to practice, these three weeks can be said to be more bitter than sweet, but I have also learned a lot from it, not only consolidating the knowledge I learned in books before, but also learning a lot of things that are not in books, and at the same time improving my hands-on operation ability and scientific and rigorous design attitude. Of course, in the process of design, I encountered many problems. First, I don't know how to choose a topic. Later, under the guidance of the teacher, I chose the topic according to the learning situation of the theory class. Then there are many obstacles in the simulation process, such as the simulation of voltage gain, the calculation of input impedance and output impedance ... the calculated value is very different from the simulation result, and I spent a long time modifying the circuit. Later, I read a lot of books and checked the information, and finally found the relevant chapters in the book and referred to them. Finally, the theoretical value is consistent with the simulation results.
Through the course design, I deeply realized that everything must be patient and meticulous. In the process of curriculum design, many calculations are sometimes inevitable; This made me feel a little uneasy: I made two mistakes because of carelessness, so I had to reluctantly start over. But when I think of my teachers' patient teaching, the social responsibility I will bear in the future, and the extremely shocking things caused by some small mistakes in the world, I can't help but remind myself at all times that I must develop a good habit of being highly responsible and meticulous. This course design gave me a rare exercise in my work style.
After just three weeks of course design, I found that my knowledge is really so poor and my ability to comprehensively use my professional knowledge is so insufficient. After studying so many courses for several years, I realized that I couldn't use it this year. I am really impatient at the thought of this, but the teacher told me that this shows that the curriculum design really makes you gain something, and the teacher's kind encouragement is injected into my mind like spring rain, which makes me full of confidence.
Finally, I want to sincerely thank my teacher. Your harsh criticism awakened me, your professionalism touched me, your teachings inspired me, and your ardent expectations inspired me. Thank the teacher for giving me a pair of strong wings today.