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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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DC-Bias Current Caused by Baseline Wander
In the underlying magnetics equation: Core_Volume ∝ Stored_Energy = ½ × L × I2, we have discussed the L (OCL) above. Now we need to know what I is.
Well before PoE came into the picture, the size of the transformers was indeed very small, because the signal-related currents sent down the line were really small. However, there was still a concern about several 1s, or several 0s (actually -1s), happening to fall in succession. This basically amounts to a big and rather long step, with an excessive DC component. It leads to baseline wander (BLW). BLW occurs because the ground or reference (DC) level is not transmitted through a transformer. It can be explained as follows: Only if we have exactly symmetrical ...

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