Using ALTLVDS_TX Serializer in Qsys

Here is Altera's responses on the subject:

The double-width modes or single-width modes are meant for the transceivers, which is used in the ALTGX megafunctions.

However, for ALTLVDS the serialization factor is limited until 10. Means if you would need 2 bit on the output, and each driving 8 bit data input which gives 16:2. It is impossible to have 16:1 from the meagfunction either in soft or hard serdes. The only way would be to pay some effort for writing own code for the serdes

ALTLVDS_TX can not support 2.5Gbps data rate on Cyclone IV GX device family, you might want to use ALTGX instead.