Keysight Technologies Achieve High-Quality Compliance Test Results Using A Top-Quality Test Fixture Application Note
Introduction When you perform compliance testing, you require the test results to confirm that a device operates as it should -- without problems at every supported speed, with every supported controller type, under hubs, and on buses loaded with other devices. You are verifying that the device meets all test specification requirements. To achieve the best test results for a high-speed serial bus, you need a top-quality test fixture such as the Keysight N7015A high-speed Type-C test fixture with high signal integrity. You can maintain signal integrity by de-embedding the effects of the fixture.
03 Keysight Achieve High-Quality Compliance Test Results Using A Top-Quality Test Fixture - Application Note The Importance of a Top-Quality Test Fixture The test fixture you use for high-speed serial bus compliance testing provides an interface between a DUT (device under test) and measurement/analysis equipment such as an oscilloscope. It provides access to the transmitter or receiver measurement points required for compliance testing. It also enables you to verify compliance systems and components to the PHY test specification. The test fixture is a critical element for performing quality compliance testing because its characteristics (such as reliability and repeatability) often compromise the specification margins for passing the electrical signal quality tests. Figure 1 shows the Keysight N27015A test fixture between a DUT and an oscilloscope. Figure 1. Test fixtures provide an interface between DUTs and measurement/analysis equipment.
04 Keysight Achieve High-Quality Compliance Test Results Using A Top-Quality Test Fixture - Application Note USB 3.1 Type-C Testing The new USB 3.1 standard (enhanced SuperSpeed USB) defines up to 10 Gbps of data transfer rate, which is twice as fast as USB 3.0 or 20 times faster than USB 2.0. These enhanced data rates are creating a need for new consumer products such as Type-C test fixtures. The new Type-C connection can carry USB 3.1 Gen 2 signals, transmit DisplayPort signals at up to 4K resolution, and handle up to 100 W of electrical power, all at the same time. USB Type-C is gaining dominance among USB connectors, for good reasons. USB Type-C ports can support many different protocols using alternate modes, which allow you to use adapters that can output HDMI, VGA, DisplayPort, or other connection types from a single USB port. Why Signal Integrity Matters Higher data rates means test fixtures and cabling can cause more signal loss. To maintain high measurement accuracy, you can use de-embedding techniques in your high-speed compliance tests to remove the text fixture and cabling effects from measurements. Then you can see the actual performance of the DUT. To achieve the de-embedding, you characterize the fixture through the measurement of S-parameters. For even better signal representation, you can combine this technique with a test fixture that is already designed for minimal signal loss. High insertion loss can compromise test margins and cause unwanted test failure. A highquality test fixture such as the N7015A addresses the problem of insertion loss. Another issue is cable loss. All cables have losses that limit the performance of a test system. The amount of the cable loss depends on the quality of the cable and its loss specifications. The longer the cable is, the greater the signal loss. Therefore, you need a cable with the lowest possible signal loss and shortest possible length. Figure 2 shows how insertion loss can help you determine the quality of a test fixture. Figure 2. Insertion loss can help you determine a test fixture s quality.
05 Keysight Achieve High-Quality Compliance Test Results Using A Top-Quality Test Fixture - Application Note De-embedding the Effects of Test Fixtures When you run a compliance test, the test signals from the DUT pass through devices such as cables or test fixtures before they are measured. As a result, you are actually measuring a combination of both the DUT signal and the effects added from the test fixture and cables used to access the DUT. By using de-embedding software such as Keysight s InfiniiSim application you can isolate the DUT to measure its performance separately from the measure signal. Figure 3 shows an example where the eye diagram pattern of the PRBS signal is measured. The cable and two fixtures in the signal path are removed by de-embedding them. To deembed the cable and fixtures, the S-parameters of each cable pair and fixture are measured and pre-installed in the InfiniiSim software. InfiniiSim then analyzes the measurement and simulation circuits and generates a correction transfer function. When the transfer function is applied to the measured waveform (V Meas ), the desired simulated waveform (V Sim ) appears on the oscilloscope s display. TX V Meas (t) Fixtures cables TX V Sim (t) V S Z Tx Z Tx VMeas (t) + - Channel element Z OSC (f) + - VS 0Ω VSim (t) Z OSC (f) Figure 3. De-embedding software such as Keysight s InfiniiSim lets you extract a DUT s signal from a measured signal.
06 Keysight Achieve High-Quality Compliance Test Results Using A Top-Quality Test Fixture - Application Note The next three figures illustrate the effects of a fixture on a signal, before and after deembedding. Figure 4 shows an example of a 13.5 Gbps PRBS signal from a J-BERT directly into a 33 GHz Keysight V-Series Infiniium oscilloscope. Figure 4. A 13.5 Gbps PRBS signal from a J-BERT directly into a 33 GHz Keysight Infiniium oscilloscope. Figure 5 shows the signal measured through Keysight s N7015A high-speed test fixture, which is inserted between the signal source (BERT) and the oscilloscope. Note the pronounced rise/fall time degradation and the closed eye. Figure 5. Note the rise/fall time degradation and closed eye when the fixture and cable are inserted.
07 Keysight Achieve High-Quality Compliance Test Results Using A Top-Quality Test Fixture - Application Note Figure 6 shows the signal measurement when using Keysight s InfiniiSim de-embedding function, which corrects for the loss of both the test fixture and the 1 m coax cable. You can see that the signal is almost perfectly restored by de-embedding the effect of the fixture. Figure 6. The signal is almost perfectly restored by de-embedding the effects of the fixture/cable. Summary High-quality compliance testing requires a top-quality test fixture. Because test fixture characteristics such as insertion loss can compromise the specification margins for passing electrical signal quality tests, you need a solution that maintains signal integrity both before and after de-embedding. Using Keysight s N7015A high-speed Type C test fixture and InfiniiSim de-embedding software ensure you will get better margins and better measurements.
08 Keysight Achieve High-Quality Compliance Test Results Using A Top-Quality Test Fixture - Application Note www.axiestandard.org AdvancedTCA Extensions for Instrumentation and Test (AXIe) is an open standard that extends the AdvancedTCA for general purpose and semiconductor test. Keysight is a founding member of the AXIe consortium. ATCA, AdvancedTCA, and the ATCA logo are registered US trademarks of the PCI Industrial Computer Manufacturers Group. www.lxistandard.org LAN extensions for Instruments puts the power of Ethernet and the Web inside your test systems. Keysight is a founding member of the LXI consortium. www.pxisa.org PCI extensions for Instrumentation (PXI) modular instrumentation delivers a rugged, PC-based high-performance measurement and automation system.
09 Keysight Achieve High-Quality Compliance Test Results Using A Top-Quality Test Fixture - Application Note Evolving Since 1939 Our unique combination of hardware, software, services, and people can help you reach your next breakthrough. We are unlocking the future of technology. From Hewlett-Packard to Agilent to Keysight. For more information on Keysight Technologies products, applications or services, please contact your local Keysight office. The complete list is available at: www.keysight.com/find/contactus Americas Canada (877) 894 4414 Brazil 55 11 3351 7010 Mexico 001 800 254 2440 United States (800) 829 4444 mykeysight www.keysight.com/find/mykeysight A personalized view into the information most relevant to you. www.keysight.com/find/emt_product_registration Register your products to get up-to-date product information and find warranty information. Keysight Services www.keysight.com/find/service Keysight Services can help from acquisition to renewal across your instrument s lifecycle. Our comprehensive service offerings onestop calibration, repair, asset management, technology refresh, consulting, training and more helps you improve product quality and lower costs. Keysight Assurance Plans www.keysight.com/find/assuranceplans Up to ten years of protection and no budgetary surprises to ensure your instruments are operating to specification, so you can rely on accurate measurements. Keysight Channel Partners www.keysight.com/find/channelpartners Get the best of both worlds: Keysight s measurement expertise and product breadth, combined with channel partner convenience. Asia Pacific Australia 1 800 629 485 China 800 810 0189 Hong Kong 800 938 693 India 1 800 11 2626 Japan 0120 (421) 345 Korea 080 769 0800 Malaysia 1 800 888 848 Singapore 1 800 375 8100 Taiwan 0800 047 866 Other AP Countries (65) 6375 8100 Europe & Middle East Austria 0800 001122 Belgium 0800 58580 Finland 0800 523252 France 0805 980333 Germany 0800 6270999 Ireland 1800 832700 Israel 1 809 343051 Italy 800 599100 Luxembourg +32 800 58580 Netherlands 0800 0233200 Russia 8800 5009286 Spain 800 000154 Sweden 0200 882255 Switzerland 0800 805353 Opt. 1 (DE) Opt. 2 (FR) Opt. 3 (IT) United Kingdom 0800 0260637 For other unlisted countries: www.keysight.com/find/contactus (BP-9-7-17) www.keysight.com/find/n7015a DEKRA Certified ISO9001 Quality Management System www.keysight.com/go/quality Keysight Technologies, Inc. DEKRA Certified ISO 9001:2015 Quality Management System This information is subject to change without notice. Keysight Technologies, 2017 Published in USA, December 1, 2017 5992-1134EN www.keysight.com