In PCB board copy and design work, we often have to debug and test the circuit board, the debugging of six types of module circuit board is one of them, in order to let you better understand the debugging technology of six types of module circuit board, first give you a brief introduction to the six types of module. The core component of six types of modules is the circuit board, whose design structure and production process basically determine the performance index of the product. The standard of six types of modules is EIA/TIA 568B.2-1, among which the most important parameters are insertion loss, return loss, near-end crosstalk, etc.
PCB board debugging technology of six types of modules
Insert Loss: Due to the impedance of the transmission channel, the attenuation of the high-frequency component of the signal will increase with the increase of the signal frequency. The attenuation is not only related to the signal frequency, but also to the transmission distance. With the increase of the length, the signal attenuation will also increase. Return Loss: Due to the impedance changes in the product, there will be local shock, resulting in signal reflection, part of the energy reflected to the sending end will form noise, resulting in signal distortion, reduce transmission performance. Such as full duplex gigabit network, will mistake the reflected signal is received signal and cause useful signal fluctuations, causing confusion, the less reflected energy, it means that the channel line impedance consistency is better, the more complete the transmission signal, the smaller the noise on the channel. The calculation formula of return loss RL is: return loss = transmitted signal ÷ reflected signal.
In the design, it is an effective means to solve the failure of return loss parameters to ensure the consistency of impedance throughout the line and match with six types of 100 ohm impedance cables. For example, the uneven distance between the layers of PCB circuit, the change of the copper conductor section of the transmission line, the mismatch between the conductor in the module and the six types of cable conductors, etc., will cause the change of return loss parameters. Near end crosstalk (NEXT) : NEXT refers to the signal coupling of one pair of lines to another pair of transmission lines, that is, when one pair of lines sends a signal, the signal received by the other pair of adjacent lines. This kind of crosstalk signal is mainly due to the adjacent winding pair through capacitive or inductive coupling. By means of compensation, to offset and weaken the interference signal, so that it can not generate standing wave is the main way to solve the failure of this parameter.
In the module trial production stage, with the theory as the guidance, computer aided design as the basis, can quickly achieve the expected results. In the design of six types of modular PCB in China, a lot of trial production work is carried out mainly on the basis of diagonal compensation theory of the line, and the expected results can also be achieved. The signal leakage caused by modules and plugs will cause signal interference between each other. In order to prevent signal interference, the conductor is twisted in the balanced link to achieve the purpose of balanced transmission. The twisted structure will cause the phase change between signals and increase the signal attenuation on the line, which is called unshielded structure (UTP). In the four balanced twisted pair pairs, each pair has different strands. The end of the cable uses a modular connector to form the connection between the connector and the connector, and a balanced structure between the conductors is formed in the interconnecting area, which is the permanent link of the six types of system. In the permanent link, the signal interference occurs in the balance line, which is called crosstalk. To solve the crosstalk problem is the core technology of high-speed communication connector manufacturing.
Contact loss between contact terminals will lead to attenuation, reflection loss and other phenomena, such loss in high-speed signal transmission, will produce obstacles and failures, to solve such problems is the core technology of high-speed communication connector manufacturing. In the connection line between the module and the plug, each pair of connecting terminals in the plug is a balance line, the balance line will lead to signal leakage and impedance loss, the biggest factor hindering communication is signal leakage. This kind of problem can be solved by studying E field and H field, or the solution can be found by studying the method of reverse attenuation, which is the core technology of high-speed communication connector manufacturing. The signal interference occurring on the balance line of E field and H field, namely electromagnetic field interference, can be described by the distribution of E field and H field.
The main parameter of electronic communication line test is the correlation measurement under the frequency sweep. Voice or data packet is attached to the frequency signal for transmission. The higher the transmission speed, the faster the frequency. The solution of signal leakage to explain the problem of socket signal leakage phenomenon, the most basic method is to collect signals in the signal concentration area and send back according to the signal leakage simulation diagram of inductance and capacitor.
In the design, the design of coupling capacitance is the key parameter, which is related to the length of the coupling line, the distance between the lines, the width, the compensation line layout, etc. Considering that the six types of system adopts four pairs of lines to transmit signals at the same time, it is bound to produce a comprehensive remote serial winding, which can be designed by analyzing and computer simulation. The trial-production process of six types of modules generally carried out by domestic counterparts is mainly after determining the main circuit, designing the compensation circuit, carrying out a large number of scheme design and sample production. After the compensation circuit and PCB layer structure are basically determined, the follow-up work is mainly through process improvement, so as to improve the performance.