3.4 Equalization

Usually the output transmission driver has a non-flat spectrum response inside the working band (ripple).

Depending on the transmitted power difference between carriers, it is possible that the response is not as flat as desired.

The physical layer is able to perform this equalization by means of signal pre-distortion, which compensates the effect of the external driver, effectively reducing the ripple and obtaining a final response closer to a flat one.

Equalization has a tight relationship with the transmission modes covered in previous sections; in fact, each transmission mode defines a particular equalization. As configurations are different for each mode, the response is also different, which requires different equalization.

An important aspect to take into account is that the objective of the equalization is to reduce ripple, giving a flatter response but keeping the average signal injection. Therefore, care must be taken to reduce the signal in some carriers and increase it in others, resulting in the same response after integrating the signal level inside the operation band.

The following figure shows an example of equalization in the PLC Cenelec-A band:

The figure shows how the ripple is reduced after equalization, keeping the same signal average in band (overlapped curves).