Readout Gigabit Transceiver Performance

Readout systems and properties

The different readout systems used in this test are listed below with links to the specific boards and the PCB material that was used, given the information that is available.

NOTE: The use of GTH transceivers in the older readouts limits the measurement comparison to 16.3 Gbit/s.

Method

All the readout boards have a similar architecture for the GT lines between the FPGA and Leap transceiver as shown below. The "ePixHRM readout" is the only one that has two boards where the GT lines go through a connector between the boards, all other readouts have the FPGA and Leap transceiver on the same board.

The receivers in FPGA GTs have a built-in functionality for measuring eye-diagrams of the captured signal using what's called "IBERT". See IBERT for UltraScale/UltraScale+ GTH Transceivers and IBERT for UltraScale/UltraScale+ GTY Transceivers for more information. With a external fiber loopback on the Leap transceiver we can generate a test pattern from the transmitters in the FPGA GTs that then travel to the Leap through the PCB and connectors, gets converted to light output, gets sent out on the fiber, comes back to the Leap and is sent back to the receivers in the FPGA GTs. The signal is therefore traversing the PCB two times and if there is any corruption on the way it will degrade the quality of the captured data.

Note that because both GTH and GTY transceivers are used there could be some slight performance difference between them that could skew the result. The GTY receivers could for example be "better" at capturing lossy data compared to the GTH in some situations.

Measurements

The measurements are done from the Vivado hardware manager by loading a specific bitfile to the FPGA with the correct GT settings and a debug file to access the IBERT interface. All files are available for download in the table below, including the Vivado project file from the left-most column. Only one eye diagram is shown for simplicity. For more information about the different equalization modes (DFE vs LPM), see UG578 for the GTY transceivers and UG576 for the GTH transceivers. All fiber connections must be cleaned before taking the measurements to remove dust as a source of error. Note that BER = bit error ratio.