Automotive Ethernet: Verifying BroadR-Reach® interfaces

Ethernet communications has been introduced in automotive networks to enable fast and cost efficient data communications, e.g. for the rearward camera or audio/video streaming. In the OPEN alliance (www.openSIG.org), the automotive industry has standardized the BroadR-Reach® physical layer as the automotive Ethernet communications standard. It will be part of the IEEE 802.3 standard. BroadR-Reach® uses full duplex twisted pair communications, enabling 100 Mbit/s data transfer. For interface verification the OPEN Alliance has specified a BroadR-Reach® conformance test with six test cases.

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Your task

BroadR-Reach® utilizes bidirectional communications similar to 1000BASE-T Ethernet, where both interfaces communicate simultaneously over the same twisted pair cable. It is therefore not possible to electrically test a single interface during data transmission without the presence of a communications partner. The OPEN alliance has specified a compliance test for BroadR-Reach® Ethernet. Like the other Ethernet compliance tests, this test focuses on the transmitter quality. The receiver is tested only with one test case, the MDI return loss measurement. The compliance test needs specific test signals from the transmitter. Each communications chipset has to be able to generate these test signals, typically activated via one of the chip’s register settings.

T & M solution

The R&S®RTO digital oscilloscope is ideal for BroadR-Reach® compliance testing due to its superior signal fidelity and automated test execution capability. For a full BroadR-Reach® compliance test, the test equipment listed in the table is needed. In addition to the oscilloscope, a signal generator is mandatory for the distortion tests with disturber and a vector network analyzer is necessary for the return loss measurements. For proper test setup, an appropriate differential probe is needed as are test fixtures for a defined connection between the DUT and the test setup. The compliance test setup, the result calculation and the documentation are automated in the R&S®ScopeSuite test software.

R&S®ScopeSuite test wizard: selecting test cases.
R&S®ScopeSuite test wizard: selecting test cases.

Application

Automated measurements with R&S®ScopeSuite test software

The R&S®ScopeSuite offers a guided test setup and automatic execution of all test cases specified by the OPEN alliance and listed in the table below. As a result, the compliance test is executed in much shorter time and with reliable and reproducible results. The test results are fully documented in a comprehensive report, including the full test setup information. R&S®ScopeSuite is a standalone application that runs on a separate PC or on the digital oscilloscope.

Test wizard with explanation of how to correctly connect to the test fixture.
Test wizard with explanation of how to correctly connect to the test fixture.

Manual limit editor

Quality requirements for signal integrity testing may differ during product development. Rohde & Schwarz supports the capability to manually change the test limit with a special editor included in the R&S®ScopeSuite software. It is possible to manually adjust the limit of each specified compliance test and therefore adjust the compliance test to customer test needs. Of course these limits are documented in the test report generated by the R&S®ScopeSuite software.

Accurate results with the R&S®RT-ZF3 frequency converter board

The distortion tests require correct transmission of a series of 12 000 signals. The algorithms specified by the OPEN alliance for the distortion tests assume that “… the disturber signal and the data acquisition clock are frequency locked to the DUT transmit clock”. This is achieved by using the transmitter’s clock as a master clock for the digital oscilloscope and the signal generator. The specified test setup for the distortion tests is shown in the last figure. Without this frequency locking, the DUT almost always fails the distortion test.

The clock of the BroadR-Reach® transmitter is specified to be 66.67 MHz. Test equipment usually allows synchronization with 10 MhH clock signals. Rohde & Schwarz supports the synchronization of the transmitter clock with a R&S®RT-ZF3 frequency converter board that transforms the 66.67 MHz clock of the BroadR-Reach® transmitter to a 10 MHz clock signal. The use of the R&S®RT-ZF3 frequency converter board leads to precise BroadR-Reach® compliance test results. The Rohde & Schwarz test solution is therefore officially listed by the OPEN alliance as BroadR-Reach® test equipment.