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In the previous course, we had a general understanding of the composition of CPU, what is the structure of the arithmetic unit and controller of CPU, and what is the main function, so in section 8, we will see how the arithmetic unit and control of CPU are realized through electronic components, or how electronic components build cpu chips.

8.1 from Triode to computer

Through the picture below, we can get a general idea of how the transistor builds our computer step by step.

(1) Triode

Because the internal working principle of the transistor is simulated, the transistor belongs to the content of this part of the course "Analog Circuits".

(2) Gate circuit, sequential circuit, trigger, combinational circuit

These are digital circuits constructed by transistors, and how these circuits work is part of the course Digital Circuits.

(3) Integrated circuit

The main research of microelectronics is how to integrate gate circuits, sequential circuits, flip-flops, combinational circuits and other digital circuits into the chip.

(4) computer

Design the schematic diagram, draw the PCB board, through the PCB board, connect all kinds of integrated chips, such as CPU, memory particles, graphics card, etc., as well as various resistors, capacitors, inductors, etc., to form the computer circuit board, which belongs to electronic content.

Of course, in addition to the above, there is also the design of the computer shell, which belongs to the product structure engineer to do.

8.2 Triode

8.2.1 symbols and physical drawings

As we have mentioned in the part of basic hardware knowledge, transistors belong to semiconductor electronic components.

8.2.2 functions of Triode

(1) the basic functions of the three-stage tube

1) basic functions

(a) by inputting a small current to the 1 end

It can be turned on and off between 2 and 3.

After the conduction between 2 and 3, the current at the 2 and 3 terminals is larger than the 1 terminal current, which is equivalent to a section of current being magnified, and this is magnified by a certain multiple.

In fact, the small current input at the 1 terminal will also enter the 3 terminal, that is to say, the current at the 3 terminal = 1 terminal small current + 2 terminal current, but because the input current at the 1 terminal is too small to be ignored, we think that the 2 terminal current is the same as the 3 terminal current.

(B) examples that are similar to the operating principle of the transistor:

The above schematic diagram of the small flow controlling the large water flow is very similar to the logic of the transistor, the small flow size will control the switch amplitude of the large water flow tube through the lever, thus realizing the small space, which also has two functions: one is to control the opening and closing of the large water pipe, and the other is that the water flow can be magnified.

2) Triode is used in two directions.

1) focus on the use of current amplification

2) it focuses on the use of its switching function (that is, for the design of binary digital circuits).

(2) current amplification function

1) focus on the amplification of current

When using the current amplification function, it is not that the transistor does not have the switching function, but the user is mainly concerned about the current amplification.

When using the current amplification function, the focus is on the amplification of the input current at the 1 end after 2 and 3 conduction (the current cannot be amplified indefinitely). If the input current at the 1 terminal increases or decreases, then the current between 2 and 3 will increase or decrease synchronously according to a certain multiple. As for the magnification, you need to check the contents of the book Analog Circuits.

2) the use of current amplification

(a) purpose: to drive and increase the operation of equipment that requires high current

When we want to use a certain current to control the work of the electronic device, but this controlled current is generally emitted by the chip, the current is generally so small that it is impossible to drive the device to work properly. At this time, you can use this amplification function to let the amplified current drive the external equipment to work.

(B) example: example of driving buzzer

For example, in this picture, the output current of the IO port of the chip is too small to drive the buzzer. At this time, by controlling a transistor, after the transistor is turned on, a voltage of 5V is added to both ends of the buzzer, which will generate a much larger current. This current can drive the buzzer.

(3) switch function

1) the key points of switch function: on and off

The function of the switch is to focus on the turn-on and off between 2 and 3 (that is, on and off). Although the current is still amplified, it does not care how much the input current between 2 and 3 is magnified, the focus is only on and off of the transistor.

In the figure above, a resistor R1 is connected between the 5V power supply and the 2 terminal, and a resistor R2 is connected between the 3 terminal and the ground, so that the output voltage of the 3 terminal can be controlled and the output of high and low level can be provided. Used to represent the binary requirement of 1max 0.

(a) turn on the Triode

After the transistor is opened through the 1 terminal, the transistor is treated as a wire between 2 and 3 (in fact, a little voltage is separated between 2 and 3), assuming that the current voltage is I, then

5V = R1mm I + R2v I

The total voltage is equal to the sum of the two resistor voltages, and 5V is apportioned between R1 and R2. As long as the resistance values of R1 and R2 are selected properly, we can control the voltage at both ends of the R2 resistor between 2.5v~5v, that is to say, the output potential of the transistor 3 is 2.5v~5v, that is to say, the output high level.

(B) turn off Triode

When the 1 terminal is no longer input current, the transistor is turned off, the 2 and 3 terminals have no conduction current, and there is no voltage at both ends of the resistor, so the output level is low, that is, 0v.

2) the use of the switch function

By controlling the switching function of the transistor, the output level can be controlled, and the transistor shows the switching characteristic, because this switching characteristic is reserved for the design of digital circuits, so the transistor has become the cornerstone of the digital circuit. As we said in the previous course, MOS transistors are now mostly used in integrated circuits, although MOS transistors and transistors are different in internal structure. However, the performance in external characteristics is similar, so in integrated circuits, mos transistors are used to replace transistors, because MOS transistors are smaller and help to improve the integration density.

8.2.3 Classification of Triode

There are two kinds of transistors. Because of their different internal structures, one is called PNP and the other is called NPN. The transistor symbols are as follows:

In order to facilitate the lecture, we marked the three ends of the transistor as 1, 2 and 3. In fact, these three ends have corresponding names, which are called base (symbol B), collector (symbol C) and emitter (symbol E). There is no difference in the physical shape of these two different transistors, which can only be distinguished by marked NPN or PNP. Due to space, the specific differences between this and that are not detailed here.

8.2.4 knowledge of transistors in depth

(1) it developer

For it development engineers who prefer programming, it is enough to understand the transistor at this level, and we only need to care about the characteristics of the transistor at the macro level.

(2) Microelectronics and hardware engineers

It is required to be very clear about the characteristics of the transistor, such as the internal structure and the relationship between voltage and current.

Our course here is a course that introduces the nature of the architecture, with strict depth control, and only talks about the content and depth that we should design in this class. If you are really interested in more in-depth knowledge of the transistor, we will explain the internal principles of the transistor in detail in the later course of analog electronics.

Author: Jiajie Studio

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