Why manipulate characteristic impedance?
In recent years, due to the improvement and application of IC power cord plug response time, its data signal transmission frequency and rate have gradually increased. Therefore, in the PCB circuit board cable, the data signal transmission (message push) has reached a unique value. It will be damaged by the PCB circuit board cable, which will also cause serious frame loss or complete loss of the transmitted data signal. This means that the "article" of the "commodity distribution company" on the PCB cable is not the amount of current, but only the transmission of wave signals or differential signals on mechanical kinetic energy.
1. What is characteristic impedance?
The definition of characteristic impedance is the frictional resistance encountered in the transmission of the alternating current circuit (AC) in the cable.
The definition of characteristic impedance is that the fluidity in the PCB route is a waveform data signal or an analog signal, which is transported on mechanical kinetic energy. The frictional resistance that this data signal will experience during transmission is called the characteristic impedance.
Differential protection characteristic impedance definition refers to the data signal frictional resistance damage between two data signals in the same layer.
The definition of coplanar characteristic impedance refers to a type of differential protection characteristic impedance, but the transmission of data signals and the distance between adjacent copper surfaces will show relative damage.
2, PCB coaxial line
PCB's coaxial line is mainly composed of the signal line, compound layer, and reference layer, all of which are indispensable. (If the signal is spread in the cable, if the length of this route is close to 1/7 of the wavelength of the signal light, the cable will be regarded as a coaxial line. Light wavelength = lamp source/frequency. Er: also It is called DK (the main parameter of the compound), that is, the relative capacitance. The Er value of different raw materials under different precise and precise measurement conditions is different, which also has great damage to the rapid spread of the signal.
3. Why do you want to manipulate the characteristic impedance?
Although all electronic components have a very high data signal transmission frequency, after transmission according to the PCB cable, the originally very high transmission frequency will be reduced or delayed. Therefore, the lower the cable length, the better.
In addition, it is very beneficial to increase the relative density of PCB traces or reduce the type and specification of cable wires. However, with the rapid frequency of electronic components or the shortening of the differential signal cycle time, the length of the cable is close to a certain range of the data signal optical wavelength (rate). At this time, the electronic components are transmitted on the PCB cable. It will mainly show an obvious "drop frame".