Why the lvds wave of true lvds tx channel is worse than the lvds wave of Emulated lvds tx when use true and Emulated lvds tx at the same time?

Hi everyone,

I accounted one problem when I use true and emulated lvds tx at the same time. For Arria V GX FPGA, I use the same lvds_tx ip for Emulated and True lvds tx which serial factor is 2, and Emulated lvds tx has one additional altiobuf ip compared to True lvds tx. In addition, the Emulated IO standard is LVDS_E_3R, True lvds IO standard is LVDS. When I view wave of the pin of Emulated tx and the pin of True tx, I find that the wave of Emulated tx will better than True tx , and the wave of True tx more likes noise, hardly see the waveform as a differential signal. It's so strange. Can anyone give some suggestion?

Thanks,

Lambert