In PCB copy board and design work, we often need to debug and test the circuit board, the debugging of the six types of the module circuit board is one of them, in order to let you better understand the debugging technology of the six types of the module circuit board, first give you a brief introduction of the six types of module. The core component of the six modules is the circuit board, whose design structure and manufacturing process basically determine the performance index of the product. The standard implemented by the six modules is EIA/TIA 568B.2-1, among which the most important parameters are insertion loss, return loss, and near-end crosstalk, etc.
Six modules of PCB board debugging technology
Insert Loss: Due to the impedance of the transmission channel, it will increase the attenuation of the high-frequency component of the signal with the increase of signal frequency. The attenuation is not only related to the signal frequency but also related to the transmission distance. As the length increases, the signal attenuation will also increase. Return Loss: Due to impedance changes in the product, local oscillation will occur, resulting in signal reflection. Part of the energy reflected in the sending end will form noise, resulting in signal distortion and reduced transmission performance. For example, in a full-duplex gigabit network, the reflected signal will be mistaken for the received signal to cause fluctuations of useful signals, causing chaos. The less reflected energy, the better impedance consistency the channel adopts, the more complete the transmission signal, and the less noise it makes on the channel.
Calculation formula of RETURN loss RL: return loss = emitted signal ÷ reflected signal.
In the design, it is an effective way to solve the parameter failure of return loss by ensuring the whole line impedance consistency and six types of cables with 100-ohm impedance. For example, the interlayer distance of the PCB line is not uniform, the copper conductor section of the transmission line changes and the conductor in the module does not match the six types of cable conductor, etc., all of which will cause the parameter change of RETURN loss.
Proximal crosstalk (NEXT): NEXT refers to the signal coupling of a pair of lines to another pair of lines in a pair of transmission lines, that is, when a pair of lines sends a signal, the signal received by another adjacent pair of lines. This kind of crosstalk signal is mainly due to the coupling of an adjacent winding through capacitance or inductance. 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 stage of module trial production, the expected results can be achieved quickly with the guidance of theory and the basis of computer-aided design. In the domestic(China) PCB design of six types of modules, based on the line diagonal compensation theory, a lot of trial production work has been carried out, and the expected results can also be achieved.
Signal leakage phenomenon caused by the module and plug mutual interference signal will happen to prevent signal interference phenomenon, conductor to twist around in balance link, achieve the goal of a balance transfer, twisted round structure will cause the signal phase change between, also increases the signal attenuation on a line, this structure is called the block structure (UTP).
In 4 pairs of balanced twisted-pair wires, the stranded distance of each pair is different, and the cable end USES modular connectors to form the connection between connectors and connectors, and the balanced structure between conductors is formed in the interconnecting area, that is, the permanent link of the six types of systems.
In the permanent link, the signal interference phenomenon occurs in the balanced circuit, which is crosstalk. Solving the crosstalk problem is the core technology of high-speed communication and credit connector manufacturing.
Contact loss between contact terminals will lead to attenuation and reflection loss, which will cause obstacles and faults in high-speed signal transmission. Solving such problems is the core technology of high-speed communication and credit connector manufacturing. In the connection line between the module and the plug, each pair of connecting terminals in the plug is a balanced line. In the balanced line, the conductor will generate signal leakage and impedance loss, and the biggest factor hindering communication is signal leakage. Such problems can be solved by studying The E and H fields or solutions that can be found by studying the reverse attenuation method, which is the core technology of high-speed communication and credit connector manufacturing. The signal interference on the balance lines of the E field and H field, namely electromagnetic interference, can be described by the distribution of the E field and H field.
The main parameter of the electronic communication line test is related to measurement under frequency sweep. The higher the transmission speed is, the faster the frequency will be, the voice or packet will be attached to the frequency signal for transmission. The solution of signal leakage is used to explain the leakage phenomenon of socket signal. The most basic method is to collect signals in the signal concentration area and send them back according to the simulation diagram of signal leakage of inductance and capacitance.
In the design, the design of coupling capacitance is the key parameter, which is related to the length, the distance between lines, width, and compensation line layout. Considering that four pairs of wires are used to transmit signals in six kinds of systems at the same time, it is inevitable to produce comprehensive remote winding, and the compensation circuit can be designed through analysis and computer simulation.
In the trial production process of six modules generally carried out by domestic peers, a large number of schemes are designed and samples are made after the main circuit is determined and the compensation circuit is designed. After the compensation circuit and THE inter-layer structure of PCB are basically determined, the follow-up work is mainly to improve the performance through process improvement.
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