Six modules of PCB circuit board debugging technology

方学放

Six modules of PCB circuit board debugging technology [Copy link]

In PCB copying and design work, we often need to debug and test the circuit board. The debugging of the six-category module circuit board is one of them. In order to let everyone better understand the debugging technology of the six-category module circuit board, I will first give you a brief introduction to the six-category module. The core component of the six-category module is the circuit board. Its design structure and manufacturing process basically determine the performance indicators of the product. The standard implemented by the six-category module is EIA/TIA 568B.2-1. The most important parameters are insertion loss, return loss, near-end crosstalk, etc. Insertion loss (Insert Loss): Due to the existence of transmission channel impedance, it will increase the attenuation of the high-frequency component of the signal as the signal frequency increases. The attenuation is not only related to the signal frequency, but also to the transmission distance. As the length increases, the signal attenuation will also increase. Return Loss: Due to the change of impedance in the product, local oscillation will occur, resulting in signal reflection. Part of the energy reflected to the transmitting end will form noise, causing signal distortion and reducing transmission performance. For example, a full-duplex Gigabit network will mistake the reflected signal for the received signal and cause fluctuations in the useful signal, resulting in confusion. The less reflected energy means that the impedance consistency of the channel line is better, the transmission signal is more complete, and the noise on the channel is smaller. The calculation formula of return loss RL is: return loss = transmitted signal ÷ reflected signal. In the design, ensuring the full line consistency of impedance and coordinating with the 100 ohm impedance Category 6 cable is an effective means to solve the failure of the return loss parameter. For example, uneven interlayer distance of PCB circuits, changes in the cross-section of copper conductors in transmission lines, mismatch between conductors in modules and Category 6 cable conductors, etc., will cause changes in return loss parameters. Near-end crosstalk (NEXT): NEXT refers to the signal coupling of one pair of lines to another pair of lines in a pair of transmission lines, that is, when one pair of lines sends a signal, the signal received by another adjacent pair of lines. This crosstalk signal is mainly due to the coupling of adjacent winding pairs through capacitors or inductors. The main way to solve the failure of this parameter is to offset and weaken its interference signal through compensation so that it cannot generate standing waves. In the module trial production stage, using theory as a guide and computer-aided design as a basis, the expected effect can be achieved quickly. In the domestic Category 6 module PCB design, the line diagonal compensation theory is mainly used as the basis, and a large amount of trial production work is carried out, which can also achieve the expected effect. The signal leakage caused by the module and the plug will cause signal interference. To prevent signal interference, the conductors are twisted in the balanced link to achieve balanced transmission. The twisted structure will cause phase changes between signals and increase signal attenuation on the line. This structure is called unshielded structure (UTP). In the 4 pairs of balanced twisted-pair cables, each pair has a different twist pitch. Modular connectors are used at the end of the cable to form a connection between the connector and the connector. A balanced structure is formed between the conductors in the interconnected area, which is the permanent link of the Category 6 system. The signal interference phenomenon that occurs in the balanced line is generated in the permanent link, which is crosstalk. Solving the crosstalk problem is the core technology for manufacturing connectors for high-speed communications. Contact loss between contact terminals will lead to attenuation, reflection loss and other phenomena. This loss will cause obstacles and failures during high-speed signal transmission. Solving such problems is the core technology for manufacturing connectors for high-speed communication. In the connection line between the module and the plug, each pair of connection terminals in the plug is a balanced line. The conductor in the balanced line will cause signal leakage and impedance loss. The biggest factor hindering communication is signal leakage. Such problems can be solved by studying the E field and H field or finding solutions by studying the reverse attenuation method. This is the core technology for manufacturing connectors for high-speed communication. The signal interference on the E field and H field balanced line, that is, electromagnetic field interference, can be described by the distribution of the E field and H field. 111, 111)]The main parameters of electronic communication line testing are related measurements under frequency sweeping. Voice or data packets are added to this frequency signal for transmission. The higher the transmission speed, the faster the frequency. The signal leakage phenomenon of the socket that causes the problem is explained by the solution of signal leakage. The most basic method is to collect signals in the signal concentration area and return them according to the signal leakage simulation diagram caused by inductance and capacitance. In the design, the design of coupling capacitors is a key parameter, which is related to the length, line distance, width, and compensation line layout of the coupling line. Considering that the six-category system uses 4 pairs of lines to transmit signals at the same time, it is inevitable that comprehensive far-end crosstalk will be generated. Through analysis and computer simulation, the compensation line can be designed. The trial production process of the six-category module generally carried out by domestic peers is mainly to design a compensation circuit after determining the main circuit, and then design a large number of scheme designs and sample production. After the compensation circuit and PCB interlayer structure are basically determined, the follow-up work is mainly to improve the process to improve the performance.

梦溪开物

What are the six modules? I can't find them in the article.

shakencity

Here is an introduction to the six types of module circuit boards. It seems that the title does not match the content and diverts the central idea.