New Contributor
Super ContributorHi,
as stated multiple times, LVDS transmitter does not use termination resistors. You can refer to the diagram that you posted above (Standard LVDS.pdf). Differential termination is placed at the receiver side, as you clarified now, the receiver is a TFT display that is equipped with required termination resistors.
LVDS IO standard is the option with lowest level and respectively lowest EMI potential, presuming you are using true LVDS rather than LVDS_E_3R IO standard.
You can optionally further reduce LVDS level by adding an external differential termination resistor at the transmitter side, there's however a risk that required RX level isn't achieved. LVDS standard doesn't require transmitter side termination. I won't expect termination to reduce signal slew-rates.
Regards
Frank
New ContributorHi,
it's not a termination (parallell) resistor I'm speaking about, it is a serial resistor and a serial resistor for shore does have impact on signal slew-rates.
Of cause you can't slow down the edges too much, one must still satisfy set up and hold demands.
Earlier in this thread I posted the document Cyclone_IV_OCT.pdf
That document shows that you, for several different logig levels, can choose some small (<100 Ohm) different Rs, serial Resistor values.
If this was a parallell single ended interface, for instance an external memory interface with address, databus and control signals you could slow down the rise and fall time on this signals, if the pcb layout is poor, using the Rs feature and that MIGHT help you to reduce the emission from the pcb enough, instead of a layout change.
This is clearly not the case for differential lines regardless type of LVDS.
That is quite pity I think and I can not really understand why?
In my world a differential pair consist of two single ended traces and they are each other's inverse. So why could you not use Rs resistors in this case?
Best regards
Kenneth
