Question
Finding a solution for 30 meter UTP using AD8145 and AD8148.
Answer
The best solution for up to 30 meters is to use the AD8148 with pre-emphasis as
the driver and the AD8145 as the receiver. It may make the most sense to start
with the 30 meter dongle solution we have given to customers in the past. The
only difference between the dongles and the regular eval boards is that the
dongles are smaller and are powered by a USB +5V AC-adapter at the driver end;
power is sent to the receiver over the fourth pair. The customer can directly
use the basic end-to-end video circuit with a few modifications, and simply
replace the dongle supplies with their +/-5V system supplies. The video signal
path requires some modifications since they are transmitting YPrPb instead of
RGBHV. The YPrPb signals have tri-level syncs embedded on either Y alone or
all three signals. Since the syncs are embedded in the video, it is not
necessary to use the sync-on-common-mode scheme that is used with RGBHV. On
the driver, they need to ground the Sync_Level, Hsync, and Vsync, inputs (pins
18, 19, and 20); this effectively disables the sync-on-common-mode function.
On the receiver, they can eliminate the sync extraction circuitry by removing
C6, C7, R7, R8, R9, R10, and R11, and disconnecting the comparator inputs and
tying them to ground (pins 12, 13, 14, and 15). They can further simplify the
receiver by replacing each of the three split terminations of 49.9 ohms + 49.9
ohms with one 100 ohm differential termination resistor. Clearly, they will
have different input and output connectors as well. The schematics, BOMs, and
gerber files for the dongle driver and receiver are attached. Please note that
the AD8145 is set for with G = 2 (the previous email mistakenly indicated G =
1).