LVDS Rx Termination Resistor

[pansoo]

rx termination

In LVDS Rx, why we use 100ohm termination resistor? Is it same with single-ended 50ohm resistor? Then, can you demonstrate it for me?

 

[paley]

lvds rx

configured as a switched-polarity current generator. A differential load resistor at the receiver end provides current-tovoltage conversion and optimum line matching at the same time, Fig. (a). For operation in the gigabits-per-second range, an additional termination resistor is usually placed at the source end to suppress reflected waves caused by crosstalk or by imperfect termination, due to package parasitics and component tolerance, Fig. (b).

please refer to H.W. Johnson and M. Graham, High-Speed Digital Design, A Handbook of Black Magic.

 

[avt]

lvds termination tolerance

what about common mode noise / etc - as there is only a differential termination - there will be imo no real reflection damping for common-mode signals (neither at the receiver (diffpair-gates -> high impedance) nor at the transmitter (current source -> high impedance) - correct ?

so what about elimination of common mode signals - not nice if reflections of common mode signals add up and will influence the common mode voltage of 1.2x V in a manner that it might get out of the 0 to 2.4 V range ....


would be nice if someone can tell me what happens to the common mode noise / disturbances from outside into the line ...