EL4543 Intersil Corporation, EL4543 Datasheet - Page 10

• Manufacturer Part Number: EL4543
• Description: Triple Differential Twisted-Pair Driver with Common-Mode Sync Encoding
• Manufacturer: Intersil Corporation

Operational Description and Application
Information
Introduction
The EL4543 is designed to differentially drive composite
RGB video signals onto twisted pair lines, while
simultaneously encoding horizontal and vertical sync signals
as common mode output. The entire video signal plus sync
can therefore be transmitted on 3 twisted pairs of wire. When
utilizing CAT-5 cable, the 4th available twisted pair can be
used for transmission of audio, data or control information.
The distribution of composite video over standard CAT-5
cable enables enormous cost and labor savings compared
with traditional coaxial cable, when considering both the
relative low price and ease of pulling CAT-5 cable.
Functional Description
The EL4543 provides three fully differential high-speed
amplifiers, suitable for driving high-resolution composite
video signals onto twisted pair or standard coaxial cable.
The input common-mode range extends to the negative rail,
allowing simple ground-referenced input termination to be
used with a single supply. The amplifiers provide a fixed gain
of +2 to compensate for standard video cable termination
schemes. Horizontal and Vertical sync signals (H
V
encode the sync information as three discrete signals of
different voltage levels. Generally, in differential amplifiers an
external V
of the differential output; in the case of the EL4543 the V
of each of the three internal amplifier channels receives a
signal from the Logic Encoding Block with encoded H
and V
fully differential video signals, with sync encoded on the
common mode of each of the three RGB differential signals.
H
differential output signals, decoded and transmitted along
with the RGB video signals to the video monitor.
SYNC
SYNC
V
H
SYNC
SYNC
EN
SYNC
) are passed to an internal Logic Encoding Block to
and V
REF
FIGURE 26. BLOCK DIAGRAM EL4543
information. The final output consists of three
SYNC
pin is used to control the common mode level
DECODING
LOGIC
can easily be separated from the
10
RCM
GCM
BCM
INA
INB
INC
+
+
+
-
-
-
+
+
+
-
-
-
EN
V
EN
V
EN
V
REF
REF
REF
SYNC
OUTA
OUTB
OUTC
+
+
+
-
-
-
SYNC
and
REF
EL4543
Sync Transmission
The EL4543 encodes H
common mode output of the differential video signals; Red,
Green and Blue respectively. Data Sheet Figure 16, 17 and 18
clearly illustrate that the sum of the common mode voltages
results in a fixed average DC level with no AC content and
illustrates the logic levels. This eliminates EMI radiation into
any common mode signal along the twisted pairs of CAT 5
cable.
Extract Common Mode Sync and Decode H
V
H
Mode sync output voltages. The relationships between
H
Table 1. The common mode levels are easily separated from
the differential outputs of the EL4543 using this simple
resistor network at the cable receiver input of each
differential channel; see Figure 27.
Twisted Pair Termination
The schematic in Figure 27 illustrates a termination scheme
for 50 series termination and a 100 twisted pair cable.
Note RCM is the common mode termination to allow
measurement of V
loads the EL4543; a little over a 100 is recommended for
RCM.
Video Transmission
The EL4543 is a twisted pair differential line driver directed
at the transmission of Video Signals through cables up to
100 feet; however, as signal losses increase with
transmission line length the EL4543 will need additional
support to equalize video signals along longer twisted pair
transmission lines. A full solution to accomplish this is the
SXGA Video Transmission System presented in the EL4543
Data Sheet. Note the inclusion of the EL9110 for signal
equalization of up to 1000ft of CAT-5 cable and common
mode extraction; see Data Sheet for additional information
on the EL9110.
Long Distance Video Transmission
The SXGA Video Transmission System makes it possible to
transmit Red, Green and Blue (RGB) video plus sync up to
1000 feet through CAT-5 cable. The input to the SXGA Video
Transmission System is the output of a video source
transmitting RGB video signals plus sync. The signals are
received initially by the EL4543; which converts the single
TYPICAL EL4543 TERMINATION DRIVER
V
SYNC
SYNC
SYNC
REF
+
-
FIGURE 27. TWISTED PAIR TERMINATION EL4543
, V
and V
50
50
SYNC
SYNC
Z
TWISTED
and the 3 common mode levels are given by
O
PAIR
=100
CM
can be regenerated from the Common
and should not be too small since it
SYNC
50
50
and V
+
-
SYNC
120
(RCM: SHOULD BE >100 )
(FOR LOADING
CONSIDERATIONS)
V
CM
signals on the
SYNC
&