How do I use TekExpress to perform a USB 3.0 Device Transmitter Test?
USB 3 Tx Testing Script
Hello and welcome to Tektronix! Today I’m going to walk through a USB 3 Device Transmitter Test using TekExpress.
A USB 3 Transmitter test consists of acquiring the signal from a USB 3 Device and running it through various tests on an oscilloscope to ensure the signal is in compliance with the USB 3 specifications. For this test, I’ll be using an external hard drive.
Here’s everything you need for the test. 2 USB cables one standard A to B cable and one A to micro cable. One Device Under Test or DUT (mine has a micro USB connector, thus the need for the micro USB cable). Two USB 3 Device Transmitter Test Fixtures, one with one A, one B, and 4 SMA connectors, and the other with two A connectors and two SMA connectors. A Device Under Test or DUT, this one has a micro USB connector. A pair of phase-matched SMA cables. An SMA to BNC cable. And a calibrated torque wrench. An AFG3000 series function generator. An MSO71254C oscilloscope with option USB 3 TekExpress software. And a keyboard and mouse.
Next I’ll be walking through the connections that need to be made between the AFG, test fixtures, DUT, and scope. Using a GPIB cable, connect one end to the GPIB port on the back of the AFG and connect the other end to the GPIB port on the back of the scope. Take the SMA to BNC cable and connect the BNC end to channel 1 of the AFG3000 and connect the SMA end to the positive SMA on the smaller of the two fixtures and make sure to tighten it with the torque wrench. Connect the A to Micro USB cable between the DUT and the large test fixture. Plug the micro side of the cable to the DUT and plug the A side of the cable into the A receptacle in the larger of the two test fixtures. Connect the A to B USB cable between the two test fixtures. Plug the B end of the cable into the B receptacle in the larger test fixture and plug the A end of the cable into the A receptacle in the smaller test fixture. Connect the phase matched SMA cables to the Dev Tx + and – SMA connectors on the large test fixture. Make sure to tighten the cables with a torque and remember to keep track which of the cables is connected to + and -. Connect the other end of the phase matched cables to channels 1 and 2 of the oscilloscope.
On the scope, launch OpenChoice Instrument Manager from the start menu. You should see a GPIB instrument show up by default, this is the scope’s internal GPIB connection. Select Search Criteria, and make sure that GPIB is selected. This will allow the scope to see instruments connected to its external GPIB connection. Click done. Click Update. You should see an additional instrument appear. This is the AFG3000 that will be used to toggle the patterns that are being output by the DUT.
In the TekScope application, click Analyze > TekExpress USBTx, which will open the TekExpress USB application. There are a lot of fields in this screen, but the way you fill them out will be dictated by what test you’re performing. The first thing to do is name your DUT (and subsequently the project folder in which all the results are saved). Select the version of USB you’ll be testing. In this case, it’s USB3 Gen1 at 5 Gbps. We’re testing a device, using a long channel, and select Micro as the connector type because our device has a Micro port. The test mode is compliance and the speed is 5 Gbps for Gen3. The compliance measurements can be performed by DPOJET, USB-IF’s SigTest software, or both. We’ll select both. The test point is set at Far End. Once all of these are set up, click Start and TekExpress will begin to run the test.
After initializing, it will ask you to turn on the DUT. This is done by supplying power to the large test fixture. Once the DUT is powered on, click OK. At this point, the DUT should be sending out an LFPS (low frequency periodic signal defined by the USB standard) and the scope should capture it. At this point, capturing waveforms, autoscaling, and measurements are automated by TekExpress and it’s just a matter of running through the battery of tests required by the USB Gen3 specification and determining whether or not the DUT passes these tests based on the results. There are two views you can use during this process, and the most useful is the Log View, which shows the steps in the compliance test process if that is of interest to the user. The whole test takes around five minutes, and at the end TekExpress produces a report on the DUT. This report contains the detailed results of each test, complete with mask tests, eye diagrams, SSC profiles, and screenshots of waveforms. The report can be saved as an HTML or MHT file that is useful for documentation, margin inspection, and failure analysis.
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