CE Pro September 2022 - 28

Networking+Home Control
HDMI CORNER by DPL Labs
Digging into Active Device
Discrepancies with Apple TV
TIME AND AGAIN we have
faced HDMI issues pertaining
to Apple TV and other settop
devices. When activated
they can fail in a couple of
common places. They can arrive
DOA or may not function
correctly when requesting
better color space from 4:2:0
to 4:2:2; in most cases, you
can forget 4:4:4. This will usually
occur with devices such
as fiber AOC (active optical
cable) or any active cable
device. Recently we were able
to do a little Apple TV R&D.
For an AOC to turn out a
DOA outcome, it must be
something serious. Either
no supply voltage, broken or
disconnected DDC transmissions,
or just defective
modules. Still, we had devices
that worked but only at 4:2:0
color space. When kicked up
to 4:2:2, the Apple TV would
revert to 4:2:0, informing the
user there was an issue.
Why would color space
be a problem? If the transmission
line was capable of
handling the entire 18Gbps
envelope, there really should
not be any issue, right? The
first test we did was on the
output stage of the Apple TV,
for which we found reasonable
output; not great but
reasonable. We took one of
the AOC cables the Apple TV
failed and ran it up on DPL's
48G instrumentation suite
and saw that when operated
at typical default standards,
28 | CE Pro September 2022
these cables worked perfectly
to 4:4:4. Why? What we
did not take into consideration
were those " Standard
Default " values that all testing
agencies use. Let's reduce
the output of the source
and do some experiments on
input sensitivity, we figured.
Typically, when a testtested.
This is normal and gets
compensated out - an easy
procedure. The source output,
in most cases, can hover between
400mv and 600mv. Fig.
1's chart compares what goes
into a cable and what comes
out. The input range starts at
0 volts with 50mv steps ending
at 300mv. It is assumed
at 4:2:2. The Red horizontal
line is the threshold to get the
display to function; above is
good and below is bad. The
defective AOC (Orange) lost
performance as the source
output approached 270mv,
visible from its Eye Diagram
beginning to breach.
Now for the real test. Let's
do the same experiment with
a known AOC that did work
with an Apple TV at 4:2:2
(Green). This was amazing -
we did not lose performance
until we got down to only
25mv! Spec for a sink is at
least 100mv and this can run
down to 25mv? Wow. But
still, why does it work on
4:2:0 and not 4:2:2? We emulated
this by dropping the
data rate to 3Gbps (4K 4:2:0)
and found the sensitivity of
the AOC improved by almost
80mv (Fig. 2's purple curve).
That reduces the margin for
error substantially with a dynamic

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CE Pro September 2022

Table of Contents for the Digital Edition of CE Pro September 2022

CE Pro September 2022 - Intro
CE Pro September 2022 - Cover1
CE Pro September 2022 - Cover2
CE Pro September 2022 - 1
CE Pro September 2022 - 2
CE Pro September 2022 - 3
CE Pro September 2022 - 4
CE Pro September 2022 - 5
CE Pro September 2022 - 6
CE Pro September 2022 - 7
CE Pro September 2022 - 8
CE Pro September 2022 - 9
CE Pro September 2022 - 10
CE Pro September 2022 - 11
CE Pro September 2022 - 12
CE Pro September 2022 - 13
CE Pro September 2022 - 14
CE Pro September 2022 - 15
CE Pro September 2022 - 16
CE Pro September 2022 - 17
CE Pro September 2022 - 18
CE Pro September 2022 - 19
CE Pro September 2022 - 20
CE Pro September 2022 - 21
CE Pro September 2022 - 22
CE Pro September 2022 - 23
CE Pro September 2022 - 24
CE Pro September 2022 - 25
CE Pro September 2022 - 26
CE Pro September 2022 - 27
CE Pro September 2022 - 28
CE Pro September 2022 - 29
CE Pro September 2022 - 30
CE Pro September 2022 - 31
CE Pro September 2022 - 32
CE Pro September 2022 - 33
CE Pro September 2022 - 34
CE Pro September 2022 - 35
CE Pro September 2022 - 36
CE Pro September 2022 - 37
CE Pro September 2022 - 38
CE Pro September 2022 - 39
CE Pro September 2022 - 40
CE Pro September 2022 - 41
CE Pro September 2022 - 42
CE Pro September 2022 - 43
CE Pro September 2022 - 44
CE Pro September 2022 - 45
CE Pro September 2022 - 46
CE Pro September 2022 - 47
CE Pro September 2022 - 48
CE Pro September 2022 - 49
CE Pro September 2022 - 50
CE Pro September 2022 - 51
CE Pro September 2022 - 52
CE Pro September 2022 - 53
CE Pro September 2022 - 54
CE Pro September 2022 - 55
CE Pro September 2022 - 56
CE Pro September 2022 - 57
CE Pro September 2022 - 58
CE Pro September 2022 - 59
CE Pro September 2022 - 60
CE Pro September 2022 - 61
CE Pro September 2022 - 62
CE Pro September 2022 - 63
CE Pro September 2022 - 64
CE Pro September 2022 - Cover3
CE Pro September 2022 - Cover4
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https://www.nxtbook.com/emerald/cepro/may_2024
https://www.nxtbook.com/emerald/cepro/april_2024
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https://www.nxtbook.com/emerald/cepro/december_2023
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https://www.nxtbook.com/emerald/cepro/october_2022
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https://www.nxtbook.com/emerald/cepro/may_2022
https://www.nxtbook.com/emerald/cepro/april_2022
https://www.nxtbook.com/emerald/cepro/march_2022
https://www.nxtbook.com/emerald/cepro/february_2022
https://www.nxtbook.com/emerald/cepro/january_2022
https://www.nxtbook.com/emerald/cepro/december_2021
https://www.nxtbook.com/emerald/cepro/november_2021
https://www.nxtbook.com/emerald/cepro/october_2021
https://www.nxtbook.com/emerald/cepro/september_2021
https://www.nxtbook.com/emerald/cepro/august_2021
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https://www.nxtbook.com/emerald/cepro/june_2021
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