Autonomous Vehicle Engineering - January 2022 - 18

Emerging Technologies
Figure 4. Example of MDI connector / Ethernet adaptor with H-MTD
and SMA.
Transmit testing
In the case of the transmitter, we are looking to ensure
that the signal characteristic is good. So, we use an
oscilloscope that acts as a receiver. The device under
test (DUT) is put into a series of known states and the
acting receiver makes sure the signal is 'valid'.
Figure 3 is an example of a backup camera view
protection mechanisms that comply with ISO 26262.
These features are welcome in the next generation
of ADAS/AV developed vehicles, but there are
also challenges to overcome. These include different
media dependent interface (MDI) cables and connectors,
securing the network, interoperability with other
vendors and technical concerns of Tx testing ensuring
linearity and PSD of PAM-N networks. It will also be
critical to validate the robustness of receivers against
electromagnetic interference (EMI) to ensure operation
in the harsh automotive environment. This is a
complex measurement that involves injecting pre-defined,
calibrated levels of noise at the RX pin of the
SerDes while monitoring its ability to clock symbols
within acceptable error limits.
Physical-layer testing
Interoperability is a real concern. Transceivers are sensitive
devices that must operate in the notoriously harsh
automotive environment that includes heat, vibration,
electro-static discharge (ESD) and EMI. This can be
broken into three different areas of testing. First, transmission
ensures that what is sent meets expectations.
Second, receiver capability establishes how reliably a
device (gateway, module, switch, PHY) receives the
correct signals. And third, the link segment shows
the performance of the passive interconnect between
transceivers known as the link segment. Physical layer
validation includes all three of these elements.
Ultimate goals for all this testing are interoperability
between vendors of different devices. There could
be over 100 different vendors that contribute to one
car and there are standards organizations that create
specifications. These applications are a way to evaluate
against known standards to ensure the data integrity
is maintained.
with lines in it. The lines equate to gaps in the transmission,
dropped packets. One or two and we can still
see the image, but we certainly don't want it to blink
black when there is a child behind the vehicle.
The camera, cable, switch and GPU or ECU, and
the vehicle braking system are each made by different
vendors. They need to work together, thereby underlining
the importance of interoperability. In addition,
the data rate is going up >100X->1000X faster than
CAN and growing a lot more complexity when there
is a higher-speed signal. The modulation type has
become increasingly complex.
Legacy standards like CAN use NRZ or PAM-2,
as compared to PAM-3 or PAM-4 for Automotive
Ethernet and automotive SerDes. So, these Tx tests
also need to check data integrity which include jitter
tests; power spectral density (a noise measurement
over a frequency range), and a linearity test to look
for variation in amplitude levels, which can cause bit
errors at the receiver.
Autonomous Vehicle Engineering - January 2022

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