The importance of impedance control technology in the design process

We should recognize that resistance and impedance are different concepts. Resistance refers to the impedance of a wire to current in the DC state, and impedance refers to the impedance of the wire to current in the AC state. Any wire has inductance. When the frequency is higher, the impedance of the wire will be far greater than the DC resistance. This article mainly talks about the meaning and importance of impedance control technology.　　 In high-speed PCB design, impedance control technology is particularly important. Impedance control technology includes the following two meanings: 　　 impedance-controlled PCB board means that the impedance of all networks on the PCB board is controlled within a certain range, such as 20-75Ω.　　Impedance controlled PCB signal line refers to the continuous impedance everywhere along the high-speed PCB signal line, that is to say, the impedance on the same network is a constant.　　Design engineers need to use transmission line theory or use EDA tools to achieve impedance control. PCB processing manufacturers must rely on advanced technology and high-performance instruments and testing techniques to ensure the accuracy of impedance control technology. Therefore, PCB manufacturers may need to change the size and spacing in the design to achieve impedance control.　 Analysis and measurement are a very important part of impedance control technology, and light board testing is especially important and accurate. Therefore, PCB design engineers must formulate the impedance and allowable errors of key signal lines in the design, and closely coordinate the work of PCB processing manufacturers to ensure compliance with all design specifications. There are many PCB signal technologies for impedance control: embedded microstrip line, asymmetric stripline, symmetrical stripline, edge-coupled coated microstrip line, edge-coupled asymmetrical stripline, radiation-coupled stripline Wait. From the perspective of the circuit and PCB design engineer, it is necessary to strictly calculate the impedance according to the system design requirements, control the geometric size of the signal line, and control the impedance and error requirements of the signal line with these key impedances, and clearly submit the document To the PCB processing factory, and request the PCB processing factory to submit a detailed report to realize the processing test. For the specific requirements of design engineers, PCB processing manufacturers usually add test strips to the periphery of the PCB design puzzle, and use advanced test technology to adjust the geometric size and spacing of key signal lines according to the processing technology.