Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
I didn't see anything directly referencing Vsig. Perhaps the spec you are referring to concerns one of the hysterysis thresholds such as Vil (ac) etc. Or perhaps the DC differential input voltage range?
Can you point out the document you are referring to?