The general machine uses a variety of models, functions of integrated circuits (ics), and several large or very large scale integrated circuits as the core, with other integrated circuits and discrete parts circuit, to form the circuit of the whole machine. These core integrated circuits may contain the functions of one or several system circuits. The circuit diagram of the whole machine, the circuit diagram of the plate and the circuit diagram of the system are all based on the circuit diagram of the integrated circuit. How should I look at the integrated circuit diagram? What to watch? What requirements should be met?
1. Look at the method and content of the integrated circuit diagram
The method of looking at the integrated circuit diagram can adopt the above-mentioned three sentences and three steps; It can also be integrated circuit as the center, on the basis of the signal path in the chip, contact and expand to the outside of the block, and then establish the connection between the integrated blocks, and finally grasp the overall situation and details; Can also be a combination of several methods, according to the map to look at the map.
When looking at the integrated circuit diagram, what should I mainly look at? It can be summarized in the following four sentences: function type, signal flow, internal and external connection, and pin function. Yuwei Electronics and everyone together to understand.
First of all, we must understand the model, type and main function of the integrated circuit used, which is the first step to understand the integrated circuit. For example, the types of integrated blocks used in cd players are mainly rf amplifiers, servo signal processing and digital signal demodulation circuits, servo drivers, system controllers (generally integrated in dsp integrated circuits) and so on. First of all, the heart must be clear about the specific model of the integrated circuit, but also to understand the type of the integrated circuit, especially to be familiar with its main functions. Various types of integrated circuits, their internal main functions and circuit structure may be similar; It is also possible that the circuit structure and circuit program are not the same, but can accomplish the same function. Familiarity with the function is the most important.
In order to quickly and correctly read the circuit diagram, the reader should consciously accumulate some information about commonly used integrated circuits, purposefully remember the specific models and types of some integrated circuits, and understand the general trend and latest situation of the use of integrated circuits. Some integrated circuits have different models, but the function is the same, and even can be directly used with each other; Some blocks have similar serial numbers, but their functions and leading legs are completely different; Some of the later integrated circuits can perform the functions of several early integrated blocks. After the reader has mastered these materials, it will show great superiority when reading the integrated circuit diagram.
Multilayer circuit board
2. Signal flow
When reading the circuit diagram, we should not be satisfied with only mastering the type and basic function of the integrated circuit, but also be familiar with the basic signal processing process. Usually, the structure of the internal circuit of the integrated block is very complex, and the reader does not need to make a detailed analysis of it, but should be familiar with the signal processing process of the internal circuit, or should be clear about its internal functional block diagram. The flow process of the signal can be seen from the block diagram, and what specific functions can be completed by the integrated block. The integrated circuit can be regarded as a component, and it is not necessary to pursue the structure and detailed working process of this component, but it should be clear that the specific functions completed by each box in the integrated circuit are familiar with the input and output signals, familiar with the waveform amplitude and frequency of the signal, familiar with the contact between the boxes, familiar with the context of the signal in the integrated block. To do this, it is a preliminary understanding of the integrated circuit diagram.
At present, some circuit diagram information data is not comprehensive enough, only the number of the integrated block and the symbol of each leading foot are given, no internal block diagram of the integrated block, no DC operating point of the integrated block leading foot is given. It will make it difficult to read the picture in depth, and the reader should look for some other information to make up for its shortcomings. In addition, many internal block diagrams often use foreign letters or abbreviations to mark, but also give beginners some difficulties, which requires readers to familiarize themselves with the Chinese meaning of letters and abbreviations as soon as possible, otherwise it is difficult to read these circuit diagrams.
Due to the characteristics of the integration process, the integrated circuit must be connected to the peripheral components through the outlet pin. In order for the integrated circuit to complete a certain function, it must be connected with the external unit circuit or component, and must also be connected with the front and back stage circuit through the lead foot. When reading the circuit diagram, it is necessary to connect the internal and external circuits of the integrated circuit, and they are the whole of a circuit system to complete some specific functions. Can not contact the internal and external circuits, will not be able to see the context of the signal, difficult to analyze the function of the circuit.
For the same integrated circuit, in the hands of different machine designers, different external circuits may be designed to connect with different component networks. Because the external discrete circuit can be ever-changing, these discrete circuit is often a difficult circuit to read the diagram. It is necessary to spend some effort to break through these difficulties, otherwise it will not be able to fully and correctly read the circuit diagram of the whole machine.
3. pin function
On the integrated circuit diagram, each pin not only needs to be marked with a serial number, but also uses a simple letter symbol to mark its name. These letter symbols are often English abbreviations, which can indicate the function of the lead foot. When looking at the integrated circuit diagram, we must attach great importance to the function of each outlet foot. The leading foot is the link between the internal and external circuits, and the connection between the leading foot and the internal functional block diagram should be clear, which is the leading foot of the corresponding internal box; It is also necessary to clarify the function of the external component of the lead foot, and the external circuit works with the internal circuit through the lead foot. Some leading pins are the input and output ports of integrated circuits, and these leading pins are of great significance when looking at circuit diagrams. When reading the integrated circuit diagram, it is necessary to observe each block diagram representing the internal function one by one, and at the same time identify the corresponding lead foot, identify the external circuit or component, which is often the main work of reading the integrated circuit diagram.
Usually, the integrated circuit leading foot and external components have a certain regularity, but the law is not static, in different models, some leading feet are not used, or the signal flow is different, the reader should be flexible to master.
Read the lead foot to do "four clear"
Reading the leading foot is a regular work and the most important work in reading the integrated circuit diagram. Familiar with the internal composition block diagram, can deepen the understanding of the function of the lead foot; Familiar with the function of the lead foot, can strengthen the understanding of the composition of the block diagram. When reading the lead foot, the following "four clear" should be done.
a. signal waveform
Many lead pins are input and output signal ports, some lead pins are switching or pulse signal, data stream or analog signal ports, and some lead pins are critical test pins. The reader should be familiar with some important signal waveform of the leading foot, understand the shape, amplitude and frequency of the signal waveform of the leading foot, which is of great significance for reading the circuit diagram and repairing the fault of the whole machine. Usually, an oscilloscope can be used to accurately read the input and output waveform shape, frequency and amplitude of the leading foot.
b. Clear direction
But also pay attention to the flow of the lead foot signal, we must distinguish the name of the foot signal, but also distinguish the foot is the signal input end, or the signal output end, or the two-way signal (i/o) port. If the signal direction is not clear, you will not be able to read the circuit diagram. Some of the leading pins are signal control terminals, and the control signal may be a switching voltage, or a data stream, or a pwm signal.
c. Relevant data
Also familiarize yourself with the data about the lead foot. It is also of great significance for reading circuit diagram and troubleshooting. First of all, we should be familiar with the data about the signal waveform, and we should clarify the range of signal amplitude and the frequency value of the signal. Secondly, it is also necessary to be familiar with the current, voltage, resistance and other data of the leading foot, especially to clarify the static and dynamic working voltage of the foot. For those dynamic, static DC voltage values are not the same as the lead foot, more attention should be paid to.
d. symbol function
According to the requirements of the original designer, each lead foot has its own purpose and name. According to the design idea of each leading foot, there are English letters or abbreviations near each foot. Professionals or maintenance personnel can know the nature and function of the foot according to the English words marked on the drawing. However, it should be noted that each multilayer circuit board manufacturer may use different abbreviations for the same nature and function of the lead foot; In most countries, multilayer circuit board manufacturers use the same or similar abbreviations. If the reader is very familiar with these abbreviations, it will bring great convenience to see the integrated circuit diagram, if not familiar with these words, it will cause many difficulties to see the diagram.
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