Datasheet

AD8192
Rev. 0 | Page 13 of 28
to 10 mA by programming the TX_OCL bit of the transmitter
settings register. The high speed outputs must be disabled if
there are no output termination resistors present in the system.
The output equalizer (pre-emphasis) can be manually confi-
gured to provide one of four different levels of high frequency
boost. The specific boost level is selected by programming the
TX_PE bits of the transmitter settings register. No specific cable
length is suggested for a particular pre-emphasis setting because
cable performance varies widely among manufacturers.
SWITCHING MODE
The AD8192 is a 2:1 HDMI/DVI source switch. The user can
select which high speed TMDS input is routed to the output by
programming the HS_CH bit of the high speed modes register and
which low speed DDC input/output is routed to the DDC common
input/output by programming the AUX_CH bit of the auxiliary
device register.
PRE-EMPHASIS
The pre-emphasized TMDS outputs precompensate the trans-
mitted signal to account for losses in systems with long cable
runs. These long cable runs selectively attenuate the high frequency
energy of the signal, leading to degraded transition times and
eye closure. Similar to a receive equalizer, the goal of the pre-
emphasis filter is to boost the high frequency energy in the signal.
However, unlike the receive equalizer, the pre-emphasis filter is
applied before the channel, thus predistorting the transmitted
signal to account for the loss of the channel. The series connection
of the pre-emphasis filter and the channel results in a flatter
frequency response than that of the channel, thereby leading to
improved high frequency energy, improved transition times,
and improved eye opening on the far end of the channel. Using
a pre-emphasis filter for compensating channel losses allows for
longer cable runs with or without a receive equalizer on the far
end of the channel. When there is no receive equalizer on the
far end of the channel, the pre-emphasis filter should allow
longer cable runs than is acceptable with no pre-emphasis. In
the case of both a pre-emphasis filter on the near end and a
receive equalizer on the far end of the channel, the allowable
cable run should be longer than either compensation could
achieve alone. The pulse response of a pre-emphasized wave-
form is shown in Figure 27. The output voltage levels and
symbol descriptions are listed in Table 7 and Table 8, respectively.
V
OCM
V
H
V
L
V
OSE-BOOST
V
TTO
V
OSE-DC
<T
BIT
V
OCM
V
TTO
V
H
V
L
V
OSE-DC
PRE-EMPHASIS OFF
PRE-EMPHASIS ON
07050-027
Figure 27. Pre-Emphasis Pulse Response
Table 7. Output Voltage Levels
DC-Coupled
PE Setting OCL Setting Boost (dB) I
T
(mA) V
OSE-DC
(mV p-p) V
OSE-BOOST
(mV p-p) V
OCM
(V) V
H
(V) V
L
(V)
0 0 0 10 250 250 3.175 3.3 3.050
1 0 2 12.5 250 312.5 3.144 3.3 2.988
2 0 4 15 250 375 3.133 3.3 2.925
3 0 6 20 250 500 3.050 3.3 2.8
0 1 0 20 500 500 3.050 3.3 2.8
1 1 2 25 500 625 2.988 3.3 2.675
2 1 4 30 500 750 2.925 3.3 2.550
3 1 6 40 500 1000 2.8 3.3 2.3
Table 8. Symbol Definitions
Symbol Formula Definition
V
OSE-DC
25
0
×
=PE
T
I
1
Single-ended output voltage swing after settling
V
OSE-BOOST
I
T
× 25 Ω
1
Boosted single-ended output voltage swing
V
OCM
(DC-Coupled)
25
2
×−
T
I
VTTO
1
Common-mode voltage when the output is dc-coupled
V
OCM
(AC-Coupled)
50
2
×−
T
I
VTTO
Common-mode voltage when the output is ac-coupled
V
H
V
OCM
+ V
OSE-BOOST
/2
High single-ended output voltage excursion
V
L
V
OCM
− V
OSE-BOOST
/2
Low single-ended output voltage excursion
1
The 25 Ω resistance in the equation is the parallel combination of the on-chip 50 Ω termination resistor and the external 50 Ω termination resistor.