The Eye Test obtains the received signal data for the given channel. This test requires that the Bit Error Ratio Tester (BERT) emits a test pattern through the Inter-Symbol Interference (ISI) channel board to then be equalized by the TUSB1146 and finally captured by the oscilloscope. This test allows for eye diagrams to be made from the signal and the eye parameters to be measured.

The oscilloscope must be configured for differential signaling. Different oscilloscopes can have different setup processes to render an eye diagram. Refer to the user manual of the oscilloscope for more information.

Figure 2-1 Eye Test Setup Diagram

The BERT needs to be configured. For these tests, the set output is a 10 Gb/s, 1:PRBS7, 400 mV amplitude pattern with no pre-emphasis or de-emphasis, and RX CDR disabled. The data trigger is automatically realigned before each trial by the BERT. When performing the JTOL test, 750 mUI Bounded Uncorrelated Jitter (BUJ) is added at the output to sufficiently stress the eye. The BERT needs to have blocking capacitors at the output for proper operation.

The TUSB1146 registers are written to through an I²C adapter, which is configured by a connected computer. When performing the "No Redriver" test, connect the output of the ISI channel straight to the channel inputs of the oscilloscope, and remove the TUSB1146 from the channel path.

Longer channel lengths can be achieved by feeding one channel into another. Note that this is not a true extension, as additional interference is added in the connection.

Once the hardware is connected and the software is configured, the setup is ready for testing. Make sure that the BERT output signal is enabled before the TUSB1146 is turned on and goes into full power state. By default, the redriver turns on in linear redriver, static EQ USB mode, making the signal output visible on the BERT or oscilloscope. Make sure the TUSB1146 is properly powered and in the CTLSEL (0xA) register, that USB3.1 mode is enabled. When these settings are true, the testing can begin.

Eye Test:

1. Configure the hardware setup in Figure 2-1. For the No EQ configuration, remove the TUSB1146 from the channel path and connect the remaining devices.

2. Select a channel length for the trial and modify the ISI channel board.

3. For static EQ, Fast AEQ, and Full AEQ configuration tests, turn on redriver and configure selected EQ type as described in EQ Configuration.

4. On the oscilloscope, measure and record the differential peak-to-peak voltage, average RMS Jitter, average eye height, average eye width, and pictures or waveform file data for the selected trial length.

5. Repeat steps 2-4 for each trial length.

This test needs to be repeated to complete the clean signal test and JTOL test for each EQ configuration (no redriver, static EQ, Fast AEQ, and Full AEQ). After final completion, there are two sets of data, each for all four EQ configurations, detailing the eye diagram data across channel lengths.