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Best Practices and Usage Tips
The following is a general procedure that should be followed when using the DS250DF810EVM in a
system.
1. Set up your data source (either BERT TX or ASIC TX) to generate a PRBS pattern of the desired data
rate.
1. Not all BERT TX sources have FIR capabilities. The DS250DF810 receiver usually does not need
much de-emphasis applied by the link partner transmitter (i.e. the BERT TX or ASIC TX). Typically
3dB of de-emphasis or 0-15% post-cursor will be adequate. If the BERT/ASIC TX has pre-cursor
capabilities, then 0-15% pre-cursor should be adequate. Most links should be operable without any
TX de-emphasis.
2. Connect the EVM in to the system. Typically this will consist of the following topology:
BERT TX or ASIC TX → SMA cables → channel_1 → Huber+Suhner cables → DS250DF810 EVM
RXn → DS250DF810 EVM TXn → Huber+Suhner cables → channel_2 → SMA cables → BERT RX or
ASIC RX
1. After making your data rate selection, push the "Initialize Channel" button on the Receiver tab. You
only need to press this once, provided you do not change data rate or adapt mode. If you want to
re-lock the CDR, simply press the "Reset channel CDR" button.
2. Check the Signal Detect, CDR lock, and Adapt Complete status indicators to see if the link is
established.
3. If the CDR is in lock, the corresponding lock LED on the EVM will light up.
3. Check the Horizontal Eye Opening (HEO) and Vertical Eye Opening (VEO) by clicking on the Acquire
HEO/VEO "On" button.
4. Check the Retimer Receiver's bit error rate by launching the PRBS pattern checker from the Receiver
tab. If necessary, tune the link partner transmitter's FIR settings to achieve the target BER.
5. Tune the Retimer TX FIR settings. It is best to demonstrate that the return path (Retimer TX to
BERT/ASIC RX) is working first before trying to optimize the Retimer RX parameters. One way to do
this would be to test over a simple channel_1 first to prove that the Retimer can drive data error-free
into the BERT/ASIC (optimizing the Retimer TX FIR as needed) then switch to the more difficult
channel_1 while keeping channel_2 unchanged.
Things to watch for:
1. At 25-28Gbps data rates, small imperfections in the channel can be problematic. Ensure that cables
are properly torqued (not over-torqued), paddle cards are properly mated with backplane connectors,
and the BERT RX is properly aligned to the incoming data stream.
2. When adding up the total channel loss, do not forget to include the loss of the test fixture and cables.
For example, the DS250DF810 EVM board plus Huber+Suhner cables have ~4dB of insertion loss
from the device output to the Huber+Suhner cable end; and another ~4dB from the Huber+Suhner
cable end to the device input.
SNLU180C – August 2015 – Revised September 2019
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Best Practices and Usage Tips
DS250DF810EVM User's Guide
21
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