Forum Discussion
New ContributorUnable to Generate Valid PAM4 Eye Diagram and BER Measurements on Stratix 10 SI E-Tile Native PHY
New ContributorAs suggested, we installed Quartus Prime Pro 24.1. However, we could not find the Transceiver Toolkit (TTK) in the System Console.
Could you please recommend the exact Quartus Prime Pro version that includes both the Transceiver Toolkit and the board example designs for PAM4 operation over the SMA connectors?
Previously, we used Quartus Prime Pro 18.1, which included board example files for PAM4 programming through the SMA interface. However, we were unable to successfully complete the Eye Viewer test, as described in our earlier correspondence.
It's Urgent, kindly respond.
Kind regards.
Regular ContributorHi,
Just wanted to follow-up. Do you have any further queries on the topic?
Regards
- pryngshu
Hi, that issue has been resolved. We are now able to generate PAM4 and NRZ signals and control them through TTK.
However, we observed that when no data is being transmitted on Tx, i.e., when the generator is turned off, a clock-like signal is still present on the Tx output. Could you please let us know what might be causing this?
Additionally, the measured data rate or clock rate are significantly different than the configured/set data rate. Could you please advise on the possible reasons for this discrepancy as well?
- Ash_R_Altera
Hi,
Here is my theory on the observation you made:
This behavior is expected and does not indicate a fault. On Stratix 10 E-tile channels, the transmitter must keep its high-speed lines toggling whenever the channel is operational, even during idle periods when no user data is being sent. Extended transmission of static levels (all 0's or all 1's) can cause Bias Temperature Instability (BTI) degradation, so the device is designed to maintain a toggling pattern to protect the channel.
For a channel that is used but temporarily idle, the recommended and common approach is to drive the TX with a DC-balanced toggling pattern such as PRBS or a clock pattern (or enable the built-in TX PMA PRBS generator). The clock-like waveform you are observing is most likely this low-rate keep-alive activity — which also helps a downstream/loopback receiver CDR retain lock, since the CDR relies on signal transitions to recover timing.
This also explains the rate discrepancy: the keep-alive/idle pattern runs at a low rate that is unrelated to your configured NRZ/PAM4 line rate, so the measured toggle frequency should be compared against the idle keep-alive pattern rather than the mission-mode data rate.
Recommended checks:
- Confirm whether your firmware/RTL (or the transceiver IP) drives a PRBS/clock pattern, or enables the TX PMA PRBS generator, when user data stops.
- Compare the measured toggle rate to that idle pattern rate, not the configured line rate.
- If you genuinely need the TX line quiet, tri-state the TX buffer (e.g., via tx_pma_elecidle or the corresponding PMA register), rather than only stopping the generator.
- Ensure the reference clock is present; if it is lost, the channel must be held in reset.
In summary, the toggling TX output on an idle channel is intended device behavior to avoid channel degradation and maintain link/CDR stability, and its rate is not expected to match your configured data rate.
Regards,
Altera Tech Support
- pryngshu
Thanks for the help so far.
I have another doubt regarding the SMA channels on the E-tile:
- My experimental setup uses single-ended signaling. Can I terminate Tx− and Rx− with 50 Ω and proceed using Tx+ and Rx+ only?
- What is the minimum acceptable peak-to-peak voltage level for the Rx input? Does the Rx input need to be differential, or can it operate with a single-ended input?
- We are getting around 500 mVpp on Tx+, which we process through the optical modulator and photodiode. After this conversion, we are getting approximately 20 mVpp, which we plan to feed into Rx+. Would this voltage level be sufficient for the Rx to reliably detect the signal?
