Reading leads to the foot to do "four understanding"

Reading lead foot is a common office reading integrated circuit diagram, is also the most close office. Knowing clearly the internal composition of the block diagram can increase the depth of the consciousness of the function of the extraction foot; A clear understanding of the function of the outlet leg enhances the understanding of the composition of the block diagram. In reading out of the foot, should do the following "four understand".

(1) Symbol function

Each lead foot has its own use and name, depending on the requirements of the original presetters. According to the presupposition of each drawing foot, there is an English book deed or a shortened word near each foot. The nature and function of the foot can be known by the professional or maintenance personnel according to the English words shown on the drawing. But should see, each manufacturer for the same nature and function of the lead foot, it is possible to use different words; In most countries,circuit board manufacturers use the same or similar reduction words. If the reader knows the expression of these words clearly, it will bring great convenience to see the integrated circuit diagram. If the people are unfamiliar with these words, it will cause a lot of difficulties to see the diagram.

(2) Signal waveform

Many lead foot is input, output signal port, a bit of lead foot is switching or electronic pulse signal, numerical flow or analog signal port, a bit of lead foot is a key test foot. The reader should know clearly that the signal waveform of the leading foot is closed, and the nominal sample, amplitude and frequency of the signal wave of the leading foot are understood. It is of great significance to read the circuit diagram and check and repair the failure of the whole machine. Generally, the use of oscilloscope can be very accurate to read the foot input, output wave name, frequency and amplitude.

(3) Relevant values

Also know the relative value of the lead foot. It is as important for reading circuit diagrams as for checking and repairing faults. First of all, it is necessary to know clearly the value of the relevant signal waveform, to clarify the range of signal amplitude, signal frequency. Secondly, it is also necessary to know clearly the current, voltage, resistance and other values of the leading foot, especially the static office voltage and dynamic office voltage of the foot. For that some dynamic, static DC voltage figures are not the lead foot, more respect.

(4) Clear direction

Also pay attention to the flow of the lead foot signal problem, be sure to divide the name of the foot signal, but also to divide the foot is the signal input end, still signal output end, still two-way signal (i/o) port. If the signal direction is not clear, there will be no way to read the circuit diagram. A bit of the lead foot is the signal choke end, choke signal may be switching voltage, may also be numerical flow, or pwm signal.

Look at the basic method of unit circuit diagram and the main internal substantive significance

How many unit circuits are made up of each system circuit? To understand the whole circuit, module circuit and system circuit, it is necessary to understand the unit circuit diagram of each system. The unit circuit is the circuit unit of the whole machine. With the development of integrated circuit technology, several or even dozens of unit circuits can be integrated into one integrated circuit. Up to now, on the circuit diagram of the whole machine, the discrete component unit circuit is less and less, so that the analysis of the unit circuit in the whole machine as less and less work, also easy. But know clearly grasp the functional principle of various unit circuits of the whole machine, it is indispensable for mastering the office principle of the whole machine, for checking and repairing the whole machine.

When reading the unit circuit diagram, we should mainly read the following internal significance: principle, function, structure, type, transformation process, digital waveform.

1. Principle and function

Each circuit system to complete a signal processing function, and each unit circuit is only to complete a signal processing process of a certain link. When reading a unit circuit, the first thing to understand is that the unit circuit sets goals and functions in the circuit system, and it mainly performs what job. Then, according to the function, as the requirements of the work, to analyze its circuit office principle. Sometimes the function and utility of a unit circuit is difficult to confirm quickly. It can be based on its position in the system circuit to assume its basic function, analyze its office principle, and then analyze and verify, and finally confirm.

Testing and testing office mainly through oscilloscope testing to achieve success. The analysis of the principle of circuit office needs to understand the reader's theoretical basis and drawing experience. Analysis of the principle of office mainly refers to the internal significance of the circuit signal and the unique place, how the circuit initiation of new signals and how to successfully achieve signal transformation.

In the analysis of circuit function and principle, along with the analysis of unit circuit structure and type. For integrated unit circuit, the specific mode of circuit can be ignored; For discrete component circuit, it is necessary to analyze the circuit structure, so as to accurately analyze the circuit type and working principle. Should see, complete the same function of the unit circuit, can use different structure and type of circuit; Even successfully achieve the same function of the circuit, you can use different office principles of the circuit.

2. Transformation process

Analysis of the circuit office principle, along with the analysis of signal transformation process. The key of analyzing circuit principle is to analyze signal transformation law. Signal analysis is clear, the principle of office will surely be solved. Signal analysis mainly analyzes the waveform, amplitude and frequency of the input signal and the output signal, analyzes their internal significance and unique place, and analyzes the principle and effect of signal transformation.

3, digital, waveform

In the analysis of the signal, to know clearly the law of the signal waveform, but also should know clearly its number. The number of signal amplitude and frequency is also a reflection of the signal's unique place and the law of the close internal significance, through the input and output signal waveform change law, analysis of signal amplitude and frequency change law, can deepen the grasp of the circuit office principle. In addition, for discrete parts of the circuit, the DC office number of the circuit is also the internal essence of the analysis, it directly affects the circuit office condition and office principle; For integrated circuits, the corresponding dynamic and static office voltage of the leading foot should also be very respectable.