How to avoid crosstalk in PCB design
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Change of the signal propagation along the transmission line from A to B, c-d will generate A transmission line coupling signal, once the end is the change of signal back to stable dc at ordinary times, there is no coupling signal, so the crosstalk occurs only in the process of signal jump, and the faster the change of the signal, the greater the crosstalk.
The coupled electromagnetic fields in space can be extracted into a set of countless coupling capacitors and coupled inductors, in which the crosstalk signals generated by the coupling capacitors can be divided into forward crosstalk and reverse crosstalk Sc on the victim network. The two signals have the same polarity. The crosstalk signals generated by coupled inductance are also divided into forward crosstalk and reverse crosstalk SL, which have opposite polarity.
The forward crosstalk and the reverse crosstalk generated by the coupled inductance capacitance are simultaneous and almost equal in size. In this way, the forward crosstalk signals on the victim network offset each other due to the opposite polarity. The reverse crosstalk has the same polarity and the superposition is enhanced. The mode of crosstalk analysis usually includes the default mode, the three-state mode and the worst case mode analysis.
The default mode is similar to the way we actually test crosstalk, that is, the infested network drive is driven by a rollover signal, the victimized network drive remains in its original state, and then the crosstalk value is calculated. This method is effective for one - way crosstalk analysis. Tri-state mode refers to the violation network driver is driven by the flip signal, and the three-state terminal of the victim network is set to a high resistance state to detect the crosstalk size. This method is more effective for bidirectional or complex topological networks. The worst case analysis means that the driver of the victim network is kept in the initial state, and the simulator calculates the sum of all the crosstalk of the default attack network to each victim network.
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