PCB News - Multilayer circuit board manufacturers teach you novices to read integrated circuit diagrams

Multilayer circuit board manufacturers teach you novices to read integrated circuit diagrams

How do multi-layer circuit board manufacturers look at the method and requirements of the integrated circuit diagram of the multi-layer circuit board
Generally, the whole machine uses various types and functions of integrated circuits (ic), and takes several large-scale or very large-scale integrated circuits as the core, and cooperates with other integrated circuits and discrete circuits to form the complete circuit. These integrated circuits, which play a central role, can contain one or several system circuit functions. Look at the circuit diagram of the whole machine, the circuit diagram of the plate and the circuit diagram of the system are all circuit diagrams with integrated circuits as the core. How should I look at the integrated circuit diagram? What to watch? What requirements should be met?

1. The method and content of reading integrated circuit diagrams

The method of looking at the integrated circuit diagram can use the aforementioned three sentences and three-step aggregation; or the integrated circuit can be the center, based on the signal path in the chip, connect and expand outside the block, and then establish the connection between the integrated blocks, And finally grasp the overall situation and details; you can also combine several methods to look at the picture according to the picture.

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 connections, and pin function. Yuwei Electronics and everyone come to find out.

First of all, we must figure out the model, type and main functions of the integrated circuit used. This is the first step in reading the integrated circuit. For example, the types of integrated blocks used in CD players mainly include rf amplifiers, servo signal processing and digital signal demodulation circuits, servo drives, system controllers (generally integrated in dsp integrated circuits) and so on. First of all, you must be clear about the specific model of the integrated circuit, and also the type of the integrated circuit, especially familiar with its main functions. Various types of integrated circuits may have similar internal main functions and circuit structures; or they may have different circuit structures and circuit programs, but they can perform the same functions. Familiarity with the function is the most important.

In order to read circuit diagrams quickly and correctly, readers should consciously accumulate information about some commonly used integrated circuits, purposefully remember the specific models and types of some integrated circuits, and understand the general trend and latest situation of using integrated circuits. Some integrated circuits have different models, but the functions are the same, and they can even directly substitute for each other; some blocks have similar serial numbers, but the functions and lead-out pins are completely different; some integrated circuits that appear later can perform the functions of several integrated blocks in the early stage. After the readers master these materials, they will show great advantages when reading integrated circuit diagrams.

2, signal flow

When reading circuit diagrams, one should not be satisfied with only grasping the types and basic functions of integrated circuits, but should also be familiar with the basic signal processing procedures. Usually, the structure of the internal circuit of the integrated block is very complicated, and the reader does not need to make detailed analysis and research on it, but should be familiar with the signal processing process of the internal circuit, or in other words, should figure out its internal functional block diagram. From the block diagram, you can see the signal flow process, and you can see what specific functions the integrated block can perform. The integrated circuit can be regarded as a component. It is not necessary to pursue the structure and detailed working process of this component, but the specific functions performed by each block in the integrated circuit should be clarified, that is, familiar with the input and output signals, and the waveform amplitude of the signal., The law of frequency change, familiar with the connection between each box, familiar with the ins and outs of the signal in the integrated block. At this point, it is considered that the integrated circuit diagram is initially understood.

At present, some complete machine circuit diagram information materials are not comprehensive enough, only the number of pins of the integrated block and the symbol of each pin are given, the internal block diagram of the integrated block is not given, and the DC operating point of the pins of the integrated block is not given. It will bring inconvenience to the in-depth reading of the picture, the reader should search for some other materials to make up for its shortcomings. In addition, many internal composition block diagrams are often marked with foreign letters or abbreviations, which is also difficult for beginners. This requires readers to become familiar 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 integrated process, the integrated circuit must be connected to the peripheral components through the lead-out pins. In order for the integrated circuit to complete a certain function, it must be in contact with the external unit circuit or component, and it must also be in contact with the front and back circuits through the lead-out pins. When reading circuit diagrams, the internal and external circuits of the integrated circuit must be connected. They are used as a whole circuit system to complete certain specific functions. If you cannot contact the internal and external circuits, you will not be able to see the ins and outs of the signal, and it will be difficult to analyze the function of the circuit.

For the same integrated circuit, in the hands of different complete machine designers, different external circuits may be designed to match different component networks. Since the external discrete circuit can be ever-changing, these discrete circuits are often difficult circuits for reading pictures. It takes some effort to break through these difficulties, otherwise it will not be able to read the circuit diagram of the whole machine comprehensively and correctly.

3, pin function

Multilayer circuit board manufacturersnot only need to mark the sequence number of each pin on the integrated circuit diagram, but also use simple letter symbols 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 pin. The lead-out pin is the link between the internal and external circuits. It is necessary to clarify the connection between each lead-out pin and the internal functional block diagram. It is the lead-out pin of the corresponding internal block; it is also necessary to clarify the function of the external component of the lead-out pin, and the external circuit is coordinated by the lead-out pin. The internal circuit works. Some lead-out pins are the input and output ports of integrated circuits. These lead-out pins are of great significance when looking at the circuit diagram. When reading integrated circuit diagrams, it is necessary to observe each block diagram representing the internal functions one by one, and also to identify their corresponding pins and external circuits or components. These tasks are often the main tasks of reading integrated circuit diagrams.

Generally, the IC lead-out pins and external components have a certain regularity, but the law is not static. In different models, some lead-out pins are not used or the signal flow is different. Readers should be flexible.

Reading leads to the "four clear"

Reading leads is a frequent task of reading integrated circuit diagrams, and it is also the most important task. Familiar with the internal composition of the 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 leads to the feet, the following "four clears" should be done.

(1) 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. Readers should be familiar with the signal waveforms of some important lead pins, understand the shape, amplitude, and frequency of the signal waveforms of the lead pins, which is of great significance for reading circuit diagrams and repairing machine failures. Usually, using an oscilloscope can accurately read the input and output waveform shape, frequency and amplitude of the pin.

(2) Clear flow direction

Also pay attention to the problem of the flow direction of the pin signal. It is necessary to distinguish clearly the name of the pin signal, but also to distinguish clearly whether the pin is a signal input terminal, a signal output terminal, or a bidirectional signal (i/o) port. If the signal flow is not clear, the circuit diagram will not be understood. Some of the lead pins are signal control terminals. The control signal may be a switching voltage, a data stream, or a pwm signal.

(3) Related data

Also be familiar with the relevant data leading to the feet. It is also of great significance for reading circuit diagrams and troubleshooting. First of all, you must be familiar with the data about the signal waveform, and clarify the range of the signal amplitude and the frequency value of the signal. Secondly, be familiar with the data on the current, voltage, resistance and other aspects of the pin, especially the static working voltage and dynamic working voltage of the pin. Pay more attention to the lead pins with different dynamic and static DC voltage values.

(4)Symbol function

According to the original designer's request, each lead has its own purpose and name. According to the design idea of each leading foot, English letters or abbreviations are marked 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 various multilayer circuit board manufacturers may use different abbreviations for the same nature and function; in most countries, multilayer circuit board manufacturers use the same or similar abbreviations. If the reader is very familiar with the expressions of these abbreviations, it will bring great convenience to viewing integrated circuit diagrams, and if they are not familiar with these words, it will cause many difficulties in viewing the diagrams.