Convert single-ended (analog) signal to LVDS
Use a high speed comparator with differential outputs, eg ADCMP561. If your TDC cannot accomodate LVPECL, then an LVPECL to LVDS converter from Onsemi should do the job. Build everything on a 4 layer board, better a 6 layer board and treat everything as an high frequency system with a frequency of the inverse of your TDC resolution (eg 20ps resolution -> 50GHz system), otherwise you are up for some (statistically) significant crosstalk between the measurement paths.