12 Replies Latest reply on Apr 11, 2019 1:28 PM by mike.jablin

    Ibis AMI RX receiver output port eye diagram probe

    roi

      hi michel,

      I have a question to your Serdes expert and need an answer ASAP. see below:

      I am currently simulating the attached simple channel in hyperlynx with Xilinx GTY transiever RX and TX IBIS-AMI files @ 6.144Gbps (Xilinx_UltraScalePlus_GTY_AMI_Kit_R1p0.zip)

       

      I built the setup according to xilinx example (shown in their instructions document) . they  use ADS.

      when using the RX model in Hyperlynx, I cannot find ibis AMI RX equalizer (DFE) output port so I cannot capture the real behivour of the entire link at the receiver output. only receiver input pins (same as die) probes are available.

      with other SWs it is possible to capture the eye diagrams at the receiver output as well as at the receiver input.

      same problem occurs with the attached Ibis AMI file (FNSR_FTLF8529P3xxx_IBIS-AMI.zip). i uploaded it to this quary because its size is smaller than Xilinx_UltraScalePlus_GTY_AMI_Kit_R1p0.zip.

       

      Do you know what is the problem here?

      do you know how can I fix it?

      does it happen with other Ibis AMI files as well?

      thanks,

      roi

        • 1. Re: Ibis AMI RX receiver output port eye diagram probe
          Community_Admin

          Roi - thanks for your question. I am going to move it to the HyperLynx specific community where it will have more visibility with subject matter experts. The Members Resources area is for general community questions and suggestions.

          • 2. Re: Ibis AMI RX receiver output port eye diagram probe
            cristian_filip

            Probing at the die will account for Rx equalization including CTLE and DFE. To see the effect of DFE alone, you can turn off Tx FFE and Rx CTLE and keep on only DFE. The DFE signature on the signal is unique, and includes some abrupt voltage shifts in the eye density plots.

            • 3. Re: Ibis AMI RX receiver output port eye diagram probe
              weston_beal

              Roi,

               

              The result you see from the IBIS-AMI analysis in HyperLynx is the output of the RX. Actually, there is no option to explicitly view the eye diagram at the pins. You could effectively get the view at the pins by setting the RX options to do nothing. As Cristian alluded to, you can verify that the eye diagram is from the output of the RX by noticing the steps in the waveforms that look something like this.

              Image result for DFE eye diagram

              Those steps are created by the DFE function in the RX.

               

              Regards,

              Weston

              • 4. Re: Ibis AMI RX receiver output port eye diagram probe
                cristian_filip

                Here is the eye density plot from our IBIS-AMI Channel Analyzer using Mentor_Tx_Channel_Mentor_Rx.ffs LineSim project and our Generic SerDes IBIS-AMI models, with FFE disabled, CTLE disabled and DFE enabled (15 taps):

                 

                Eye_density_plot.png

                In addition to that, in the last page of the wizard you can choose the "Extended" option from the dropdown list available for the AMI model debug info log. This will generate the impulse responses before and after Rx Init, that you can load in EZwave:

                Impulse_responses.png

                You will see the effect of the DFE taps in the impulse response after Rx Init.

                Moreover, in the Reporter's window the values of the normalized DFE taps are displayed:

                Reporter.png

                 

                Hope this answers the question.

                Cristian

                • 5. Re: Ibis AMI RX receiver output port eye diagram probe
                  roi

                  Guys,

                  your answers were very helpful.

                  many thanks,

                  Roi

                  • 6. Re: Ibis AMI RX receiver output port eye diagram probe
                    cristian_filip

                    If you really want to probe at the pin, you can add a dummy differential symbol (no model assigned to it) and select it in the dropdown list of the receiver probe:

                     

                    Dummy_symbol.png

                     

                    You will note that in the "Configure AMI Models" page of the wizard the "Configure Rx AMI..." button will be grayed out because there is no model assigned to this symbol.

                    Here are the results without DFE:

                     

                    Probbed_at_pin.png

                     

                    You can now compare the two eye density plots and notice the difference.

                    • 7. Re: Ibis AMI RX receiver output port eye diagram probe
                      mike.jablin

                      I tried this dummy symbol method but did not get a good eye diagram.

                       

                      With the probe set normally at the RX+ symbol, I get the eye diagram with DFE:

                      I can configure the receiver model to use its low power equalization instead of DFE and get this:

                      So far, so good.  But when I set the probe to the dummy symbol, I get this:

                      It's so smooth it looks like it's not recovering a clock at all.  There's a check box called "Ignore rx AMI model clock ticks", which seemed like a good idea since there's no AMI model for the receiver.  But that gave me the same result:

                      Are there other unusual settings you used to get your result without DFE?

                      • 8. Re: Ibis AMI RX receiver output port eye diagram probe
                        mike.jablin

                        Also, is the dummy symbol method valid if I have an s-parameter model for the receiver die?  The IBIS file for the FPGA has no curves in it; it just calls out the AMI files.  They have s-parameters to model the die.  It seems that any nonlinear loading effects of the receiver must be modeled in the Waveform call of the receiver DLL, because s-parameters are only linear.  Thus, if there is no receiver AMI / DLL assigned, is the physical load of the receiver missing from the simulation?  Or do they do it that way because any nonlinear effects are too small to matter, and the receiver model only handles the DSP?

                        • 9. Re: Ibis AMI RX receiver output port eye diagram probe
                          cristian_filip

                          Without having any information about your models it is hard to precisely say what is going on with your experiments, but I am guessing that your Rx model has other signal conditioning blocks such as CTLE, AGC and (less) possibly FFE. Although you turn off the DFE the eye is still open because of those additional blocks. I would suggest contacting our support if you need better assistance.

                          • 10. Re: Ibis AMI RX receiver output port eye diagram probe
                            weston_beal

                            Mike,

                             

                            For your first question about the view; it might make sense. If the equalization is really good, it could open an eye that appears to be non-existent. Try changing the color map range by unselecting the auto range and move the sliders.

                             

                            On the other hand, your second question indicates that there might not be an eye opening to work with. If the receiver analog effects like termination are not in the IBIS model but have to be included through the DLL then the signal at the component pins is not complete. In this situation you would need to get the unequalized eye from the Rx model with the equalization features all disabled.

                             

                            Weston

                            • 11. Re: Ibis AMI RX receiver output port eye diagram probe
                              mike.jablin

                              Thanks, that might be it.  If I move the range sliders around it looks like there's a hint of a periodic signal.

                              • 12. Re: Ibis AMI RX receiver output port eye diagram probe
                                mike.jablin

                                The model I'm working with is the Xilinx Ultrascale Plus GTH, which you may have, but I didn't want to post it here because I got it under NDA.  I'm using their example simulation which they show in the user guide. The example channel is pretty lossy.  I'll see what details I can get from them about the models, now that I know a bit more about what I'm seeing and how IBIS AMI is supposed to work...