Cyclone V LVDS differential termination and RZQ

[Altera_Forum]

Hello, I am designing a board with differential LVDS interfaces (receive). 

I want to use the internal differential termination Rd and the manual is not very explicit on whether the RZQ resistor has to be present or not. Does anyoen has a definite answer ?  Thanks Pascal

[Altera_Forum]

I don't agree. The device manual is quite clear about the fact that Rd on-chip-termination for LVDS inputs doesn't use calibration - and thus doesn't depend on RZQ.

[Altera_Forum]

--- Quote Start ---  I don't agree. The device manual is quite clear about the fact that Rd on-chip-termination for LVDS inputs doesn't use calibration - and thus doesn't depend on RZQ.  --- Quote End ---    Hello, well if you can point out where in the manual it is stated as clearly as you write it in your reply, I may  have missed it. The manual talks about RZQ and Rs,Rt, but never mention that Rd is not concerned. It also implies that Rd does not track PVT variations then. Anyway, I ended to this conclusion, and having your advice helps solving this uncertainty (at least for  me). Thank you.  Pascal

[Altera_Forum]

You may want a clearer explanation in the manual, but it does distinguish between "OCT with calibration" and just "OCT" (without calibration). There's a table summarizing all available OCT variants, it says which of it have calibration. 

 Technically, OCT calibration is provided for those termination schemes that are using transistors as load, basically the same feature that provides programmable current strength. Differential Rd uses fixed termination, GX transceivers have calibrated differntial OCT.

[Altera_Forum]

--- Quote Start ---  You may want a clearer explanation in the manual, but it does distinguish between "OCT with calibration" and just "OCT" (without calibration). There's a table summarizing all available OCT variants, it says which of it have calibration.  Technically, OCT calibration is provided for those termination schemes that are using transistors as load, basically the same feature that provides programmable current strength. Differential Rd uses fixed termination, GX transceivers have calibrated differntial OCT.  --- Quote End ---    Thank you very much, it's all clear now. Pascal

[Altera_Forum]

This doesn't make any sense : Cyclone 5 does not have OCT Calibration for LVDS interface. Based on Cyclone 5, you have %40/50 variations based on PVT. How come there is no calibration. Is there any Altera AE looking for this thread?

[Altera_Forum]

RZQ is used for External memory interface IP ,such as DDR3. LVDS can use only internal register,which can set in assignment editor.