Analog Application Note
AAN-5
Demo Kit Drives VGA Over 300m of CAT5
Due to its low cost, wide availability and predictable electrical characteristics, standard un-shielded CAT5 twisted-pair
interconnect is a good choice for long-distance transmission of electrical information. Transmission of video signals over
CAT5 cable requires the use of a transmission and a receiver circuit. This application note describes the Exar video with
encoded VSYNC and HSYNC over twisted pair solution that will handle VGA (640x480) and SVGA (800x600) formats. (A
solution for XVGA (1024x768) format is in development). Using the circuitry in this demo kit allows driving unshielded
CAT5 twisted pair up to 300m in length.
Block Diagram
Figure 1 shows the simplified block diagram of the Exar video over twisted pair demo kit. The block diagram shows
the CEB500 Encoder (single to differential driver) that encodes the five single-ended data lines (R, G, B, VSYNC, and
HSYNC) into 3 differential lines that are ready to be transmitted over unshielded twisted pair of up to 300m. The CEB501
receives the 3 encoded differential signals, equalizes the line loss, and decodes the signals back to true R, G, B, VSYNC,
and HSYNC.
CEB501 Receiver Board
CEB500 Transmitter Board
R
G
B
DECODER
Single-ended
to differential
Differential to
single-ended
V SYNC
HSYNC
GND
R
G
B
V SYNC
RGB
&
V SYNC / H SYNC
RGB
&
V SYNC / H SYNC
VGA DSUB
Connector to
Monitor
HSYNC
GND
0 - 300m CAT5 Cable
Figure 1: Demo Kit Block Diagram
Exar Corporation
48720 Kato Road, Fremont CA 94538, USA
www.exar.com
Tel. +1 510 668-7000 - Fax. +1 510 668-7001
Rev 1A
VGA DSUB
Connector from
Computer
ENCODER
AAN-5 Demo Kit Drives VGA Over 300m of CAT5
Introduction
Analog Application Note
Schematic Discussion:
Typical CAT5 cable consists of 4 separate twisted-pair
channels, usually 24 AWG wire. For a remote video
system, this allows 3 channels to carry video information
while allowing an additional channel to carry audio and/or
control information. Twisted-pair transmission allows for
differential signaling. This provides better quality video by
allowing a larger signal swing and suppression of evenordered harmonic distortion. Single-ended RGB video
information is first converted to a differential signal before
transmission. At the receiver, the signal is then converted
back to single ended in order to drive a standard video
monitor.
Transmitter Board - CEB500
For long distance transmission, the cables’ electrical
characteristics will attenuate higher frequency components
of the signal. For good quality video, this must be corrected
for at the receiver by incorporating a frequency response
equalization function to selectively boost higher frequency
components back to their original values.
Another effect of long distance cabling is drop in DC gain
due to the finite resistance of the cable. This will affect
contrast levels of the reproduced video picture.
The CEB500 receives VGA format video information
directly from the standard 15 pin DSUB connector located
on the back of the personal computer. Figure 2 shows the
schematic for the CEB500. It consists of a power supply
voltage regulator, three single to differential cable driver
circuits (RED, GREEN, BLUE video), a HSYNC and VSYNC
encoder block, and a common-mode voltage generator.
The CEB500 runs off of a single 5V supply. In addition, ESD
protection diodes are included on all inputs and outputs.
Vertical and Horizontal sync pulses are encoded into
three separate common-mode levels to drive each of the
channels. VSYNC and HSYNC are expected to be standard
logic levels. The circuit creates the following weighting
table for the 4 possible combinations of VSYNC and HSYNC.
As can be seen from the table, all four combinations create
the same levels of 3.0, 2.0 and 2.5 among the various
channels. This allows for cancellation of EMI interference
between channels during switching.
Vsync
RED CM
Green CM
BLUE CM
Low
High
3.0
2.0
2.5
Basic VGA Information
Low
Low
2.5
3.0
2.0
A typical computer graphics interface uses the standard
VGA video format, designed to drive a 640x480 pixel array.
Higher resolution formats allow for larger pixel arrays.
This Exar solution will handle VGA (640x480) and SVGA
(800x600) formats. (A solution for XVGA (1024x768)
format is in development)
High
Low
2.0
3.0
2.5
High
High
2.5
2.0
3.0
Rev 1A
Hsync
The VGA type interface consists of three video channels
and two timing or synchronization channels. The 3 video
channels convey separate true RED, GREEN, and BLUE
information. The timing signals are for the standard
horizontal (HSYNC) and vertical (VSYNC) pulses.
To run the 5 separate video information signals over three
channels, Exar’s driver/receiver solution encodes the HSYNC
and VSYNC information onto the common-mode level of the
three video channels. This is done in a manner in which
the encoded levels cancel EMI radiation which may corrupt
the video signal. Common-mode levels are then detected
at the receiver and de-coded into the original HSYNC and
VSYNC information.
©2008-2013 Exar Corporation AAN-5 Demo Kit Drives VGA Over 300m of CAT5
Basic CAT5 Information
2/13
Rev 1A
Analog Application Note
0.1uF
R
49.9
1/2 CLC2000
X
RP
X
RN
X
GP
X
GN
X
BP
X
BN
100
75
649
AAN-5 Demo Kit Drives VGA Over 300m of CAT5
510
2260
510
2260
225
49.9
1/2 CLC2000
VCM
RSYNC
0.1uF
G
49.9
1/2 CLC2000
510
100
2260
75
649
510
2260
225
49.9
1/2 CLC2000
VCM
B
VSYNC
0.1uF
49.9
1/2 CLC2000
100
2260
150
649
Rev 1A
510
150
510
2260
225
1k
49.9
1/2 CLC2000
1k
0.1uF
1/2 CLC2005
VSYNB
HSYNCB
VCM
100k
1k
1k
200
1k
1k
1/2 CLC2005
VSYNB
1/2 CLC2005
RSYNC
VSYNC
49.9
1k
100k
1k
1k
To all ESD Diodes
200
100
1k
1/2 CLC2005
SD
HSYNCB
Vout
To Circuit Power
HSYNC
ADJ
49.9
Figure 2: CEB500 Transmitter/Encoder Schematic
©2008-2013 Exar Corporation 3/13
Rev 1A
Analog Application Note
Green channel receives VSYNC information directly from
the sync input. This signal should be at 0-5V logic levels
to ensure correct common mode encoding. The other
channels receive their sync information from Schmidt
trigger buffered inputs, so these are less critical. Red
channel receives its weighted common-mode levels from
a difference circuit (discussed below). The 2260Ω resistor
values are set to limit the common-mode swing to ±0.5V.
Output series resistors R5 and R6 are set to 50Ω for proper
cable termination.
The detail of the BLUE channel driver is detailed in Figure
5. This circuit is basically the same as the RED and GREEN
Figure 6 shows detail of the support circuit for the transmit
path. It consists of two Schmidt-Trigger input stages, a
difference amplifier, and a common-mode reference
generator.
The Schmidt triggers allow for input buffering of the Vsync
and Hsync logic levels while providing switching hysteresis
between switching states. This allows for immunity to
false switching events that may be caused by a noisy input
level.
The outputs of the Schmidt triggers drive the difference
amplifier. The difference amplifier provides the RED
weighting function of (Vsyncb-Hsyncb) which in turn drives
the common-mode input control of the RED channel.
To allow for single supply operation, a low impedance
common-mode reference level is needed to drive all three
channels. The reference generates a mid-supply from a
filtered resistor divider placed between the power rails.
Low cost CLC2005 amplifiers are required for these
functions due to their rail to rail output capability.
Rev 1A
R
channels except that it contains two common-mode
inputs. This allows for the VSYNCB and HSYNCB summing
operation to provide the desired weighting.
AAN-5 Demo Kit Drives VGA Over 300m of CAT5
Details of the channel drivers for RED, GREEN and BLUE
channels are shown in figures 3, 4, 5 respectively. The video information is AC coupled to the inputs of the CLC2000.
The dual CLC2000 is used to provide both an inverting
and a non-inverting configuration to create the differential signals needed to drive the CAT5 cable. The common
mode sync information is added through the 2260Ω resistors (i.e. R7 and R8 in figure 3, etc.). The 100Ω resistor is
used to set the DC bias condition to the generated VREF
level (2.5V) as well as to set the input impedance to 75Ω.
The net input impedance is the 100Ω resistor in parallel
with the 255Ω impedance of the inverting amplifier.
0.1uF
C1
49.9
1/2 CLC2000
RP
U2-A
R5
R3
R11
100
RSYNC
2260
75
R10
R4
225
649
2260
R8
R7
510
510
R2
R1
49.9
RN
1/2 CLC2000
U2-B
VCM
R6
Figure 3: RED Channel Schematic
©2008-2013 Exar Corporation 4/13
Rev 1A
Analog Application Note
G
0.1uF
C4
49.9
1/2 CLC2000
GP
R19
AAN-5 Demo Kit Drives VGA Over 300m of CAT5
U1-A
R16
R12
100
VSYNC
2260
75
R13
R18
2260
R15
649
225
R14
510
510
R17
R9
49.9
GN
1/2 CLC2000
U1-B
VCM
R20
Figure 4: GREEN Channel Schematic
B
0.1uF
C6
49.9
BP
1/2 CLC2000
VSYNCB
R29
150
U3-A
R31
R23
HSYNCB
100
R28
649
2260
R24
2260
R25
510
Rev 1A
R22
R26
150
510
R27
255
R21
49.9
1/2 CLC2000
BN
R30
U3-B
VCM
Figure 5: BLUE Channel Schematic
©2008-2013 Exar Corporation 5/13
Rev 1A
Analog Application Note
1k
R41
VCM
0.1uF
C7
1/2 CLC2005
U5-B
100k
1k
R39
1k
R36
R45
200
1k
1k
R38
1/2 CLC2005
R37
RSYNC
R44
VSYNCB
1/2 CLC2005
U4-A
VSYNC
R50
U5-A
49.9
100k
R35
1k
1k
R32
1k
1k
R43
R42
200
HSYNCB
R34
1/2 CLC2005
R33
U4-B
HSYNC
Rev 1A
R49
49.9
Figure 6: Transmit Common-Mode Sync Control with Common-Mode Reference Generator
©2008-2013 Exar Corporation AAN-5 Demo Kit Drives VGA Over 300m of CAT5
1k
R40
6/13
Rev 1A
Analog Application Note
Schematic Discussion:
One of the two CLC2000 amplifiers performs differential to
single ended conversion, while the second performs both
the DC boost and high frequency equalization function.
Receiver Board - CEB501
Figure 9 shows the schematic for the CEB501. It consists
of a power supply voltage regulator, three differential to
single cable driver circuits with adjustable equalization
circuits (RED, GREEN, BLUE video), a HSYNC and VSYNC
decoder and driver block and a common-mode voltage
generator. As with the CEB500, ESD protection diodes are
included on all inputs and outputs.
All three receiver channels are identical, one channel is
illustrated in Figure 7. Each channel:
•
Provides proper cable termination
•
Allows for common-mode level sensing of encoded
Hsync and Vsync signals
•
Provides differential to single ended conversion
•
Allows for dual pole/zero frequency equalization
•
Provides DC gain adjustment for contrast control
•
Drives standard single or dual doubly-terminated video loads
Note: One switch always has to be ‘ON’. If all
switches are ‘OFF’, no video signal will appear at
the output.
Table 2 below provides suggested DIP switch settings for
cable lengths ranging from 0M to 300M in 25M increments.
Output series resistors R27 are set to 75Ω for proper driving a doubly-terminated video load.
Cable Length
(meters)
Resistors R1 and R2 provide a high impedance commonmode sense point for extraction of the common-mode sync
signals. An additional network (shown in figure 7) sums
the RED and BLUE to provide (RED+BLUE) common-mode
for comparison against the GREEN for VSYNC extraction.
Resistors R3 to R6 along with capacitor C1 form the cable
termination network. It allows low DC loading while providing proper cable termination at higher frequencies.
X
510
1k
R7
R8
DIP Switch Position
1
2
3
4
1 to 150
OFF
ON
OFF
OFF
151 to 200
OFF
OFF
ON
OFF
201 to 300
OFF
OFF
OFF
ON
Table 2: Suggested DIP Switch Settings for Various Cable
Lengths
Rev 1A
RP
AAN-5 Demo Kit Drives VGA Over 300m of CAT5
Ability to adjust both DC gain and frequency equalization
for different CAT5 cable lengths is incorporated through a
fixed switch mechanism. Three, 4-position DIP switches
(one for each channel) allow for four different settings
for cable lengths ranging from 0M to 300M. This allows
for quick and simple control which will adjust for both DC
(contrast) and high frequency equalization simultaneously.
100n
R1
500
R3
56
R2
500
R4
56
24.9
C1
R6
R5
1k
RN
255
X
1/2 CLC2005
R9
255
VCMR
R10
RBCM
GP
VCM
same circuit as red
X
500
R27
1/2 CLC2005
4
VCMG
GN
BP
R
75
500
X
200
280
1000p
330p
56.2
620
3
same circuit as red
X
500
200
250
100p
470p
100
604
2
500
VCMB
BN
X
RBCM
200
250
330p
47p
100
549
1
200
300
47p
22p
50
499
Figure 7: RED, GREEN, and BLUE Cable Equalizer Schematic
©2008-2013 Exar Corporation 7/13
Rev 1A
Analog Application Note
Figure 8 details the receiver support circuitry. It uses three
low-cost, rail to rail output CLC2005 dual amplifiers.
resistor.)
One half (single amplifier) of a CLC2005 is used to generate a low-impedance common-mode reference voltage
that is necessary for single supply operation.
Three amplifiers are used to as a gain boost for the extracted sync signals. This includes the RED and BLUE along
with the (RED+BLUE) signal that was derived from the
resistor network discussed above. This provides a more
robust sync detection circuit. (Note: Additional frequency
equalization can be added here by placing an equalization
capacitor in parallel with the gain setting (R85, R87, R89)
10k
R93
10k
R94
0.1uF
C38
VCM
1/2 CLC2005
U8-B
1k
R92
1k
R85
1/2 CLC2005
RBCM
75
VCMG
VSYNC
R90
U10-B
1k
R88
1k
R89
1/2 CLC2005
VCMB
U8-A
0.0047uF
1k
75
1/2 CLC2005
R86
HSYNC
R91
U9-B
1k
R87
1/2 CLC2005
VCVR
U9-A
Figure 8: Adjustable Receiver Schematic
©2008-2013 Exar Corporation 8/13
Rev 1A
Rev 1A
1/2 CLC2005
U10-A
AAN-5 Demo Kit Drives VGA Over 300m of CAT5
The two remaining amplifiers are used to both decode the
horizontal and vertical synchronization signals and to provide output drive into a standard 150Ω doubly terminated
load.
Analog Application Note
RBCM
RP
RN
GP
GN
BP
BN
500
500
VCMR
VCMG
VCMB
56
56
25
1/2 CLC2005
100n
1k
VCM
VCM
510
255
255
RBCM
1k
1/2 CLC2005
1k
1k
0.0047uF
1k
330p
200
100p
200
1000p
200
280
47p
250
470p
250
330p
280
22p
200
47p
1/2 CLC2005
1k
1/2 CLC2005
1k
100
56.2
100
100
50
VCMG
SD
AAN-5 Demo Kit Drives VGA Over 300m of CAT5
X
X
500
500
same circuit as red
X
X
500
500
same circuit as red
X
X
0.1uF
VCMB
1k
1/2 CLC2005
Rev 1A
Vout
ADJ
4
3
2
1
1/2 CLC2005
1/2 CLC2005
To all ESD Diodes
To Circuit Power
1/2 CLC2005
620
604
549
449
75
75
75
X
X
Same as Red Channel
R
B
G
X
Same as Red Channel
VSYNC
HSYNC
X
X
Rev 1A
9/13
©2008-2013 Exar Corporation 10k
10k
VCMR
Figure 9: CEB501 Receiver/Decoder/Equalizer Schematic
Analog Application Note
Set-Up and Operation
1. Before starting, connect the remote monitor directly
to the VGA output on the back of the PC. For
Windows-XP operating system, right-click and select
PROPERTIES , then select the SETTINGS tab. Select
the secondary monitor and set the desired resolution.
Choose either 600x480 (VGA),800x600 (SVGA),
or 1024x768 (XVGA) resolution. When complete,
disconnect the monitor from the PC and proceed.
2. Both boards require a separate DC power supply.
Nominal supply voltage should be set to 5V.
Maximum supply voltage is 6V. Set supply values
and with power off, connect to the VCC and GND
terminals located on each board.
3. Using a standard VGA wiring harness, connect the
VGA 15P DSUB located on the back of a standard PC
to the 15P DSUB located on the CEB500 transmitter
board.
4. Choose the desired CAT5 cable length and connect
the CEB500 to the CEB501 through the modular RJ45
connectors.
6. Connect the monitor or other display device to the
15P DSUB connector on the CEB501 board.
7. Power up DC supplies. First turn on the supply for
the CEB500, then turn on the supply for the CEB501.
Video should now appear on the remote monitor.
Note: Below is a link to a free download that allows the PC
to generate a number of useful video test patterns. This is
useful for demonstrating the Exar VGA video over twisted
pair solution.
http://www.spectracal.com/
Select Downloads -> HTPC Pattern Generator.
Follow the installation procedure which will place an icon
on your desktop. Click the icon to start the CalMAN Pattern
Generator.
5. Based upon the length of the CAT5 cable, use Table
AAN-5 Demo Kit Drives VGA Over 300m of CAT5
2 above to determine which one of the 4 switch
settings to use for cable equalization. Set the same
switch for each of the three channels. As mentioned
above, only set one of the four individual switches
ON for each DIP switch. All other should be set in the
OFF position.
Rev 1A
©2008-2013 Exar Corporation 10/13
Rev 1A
Analog Application Note
Bill of Materials
Manufacturer
Manufacturer P/N
Description
Qty on CEB500
Qty on CEB501
1
Circuits West
CEB500
2
Circuits West
CEB501
Printed Circuit Board
1
0
Printed Circuit Board
0
1
3
Exar
CLC2000
Dual OP-Amp
3
3
4
Exar
CLC2005
Dual OP-Amp
2
3
5
CTS
208-4
4POS SPST Dip Switch
0
3
6
Tyco
1734344-1
15P DSUB Connector
1
1
7
EDAC
A00-108-660-450
RJ45 Modular Jack
1
1
8
Diodes Inc.
SDA004-7
Dual Schottky Barrier
3
3
9
Diodes Inc.
1N4148-T
1N4148 ESD Diode
11
11
10
MicroChip
MCP1825-ADJE/AT
500mA LDO
1
1
11
Panasonic
24.9 Ω Resistor
0
3
12
Panasonic
49.9 Ω Resistor
8
3
13
Panasonic
56.2 Ω Resistor
0
9
14
Panasonic
75 Ω Resistor
2
5
15
Panasonic
100 Ω Resistor
4
7
16
Panasonic
150 Ω Resistor
2
0
17
Panasonic
200 Ω Resistor
2
12
18
Panasonic
249 Ω Resistor
0
6
19
Panasonic
255 Ω Resistor
6
6
20
Panasonic
280 Ω Resistor
0
3
21
Panasonic
300 Ω Resistor
0
3
22
Panasonic
475 Ω Resistor
0
3
23
Panasonic
499 Ω Resistor
0
10
24
Panasonic
510 Ω Resistor
6
6
25
Panasonic
523 Ω Resistor
0
3
26
Panasonic
549 Ω Resistor
0
4
27
Panasonic
649 Ω Resistor
3
0
28
Panasonic
1 kΩ Resistor
8
9
29
Panasonic
2 kΩ Resistor
0
4
30
Panasonic
2.26 kΩ Resistor
6
0
31
Panasonic
10 kΩ Resistor
3
3
32
Panasonic
100 kΩ Resistor
2
0
33
Panasonic
107 kΩ Resistor
1
1
34
Panasonic
22 pF Capacitor
0
3
35
Panasonic
47 pF Capacitor
0
6
36
Panasonic
100 pF Capacitor
0
3
37
Panasonic
147pF Capacitor
0
2
38
Panasonic
330 pF Capacitor
0
4
39
Panasonic
470 pF Capacitor
0
3
40
Panasonic
1000 pF Capacitor
0
3
41
Panasonic
0.1 uF Capacitor
6
12
42
AVX
6.8 uF Capacitor
5
5
43
AVX
220 uF Capacitor
3
0
11/13
Rev 1A
©2008-2013 Exar Corporation AAN-5 Demo Kit Drives VGA Over 300m of CAT5
Item
Rev 1A
Analog Application Note
Figure 12: CEB500 - Top View
Figure 13: CEB501 - Top View
Figure 14: CEB500 - Bottom Silkscreen
Figure 15: CEB501 - Bottom Silkscreen
Figure 16: CEB500 - Bottom View
Figure 17: CEB501 - Bottom View
Rev 1A
Figure 11: CEB501 - Top Silkscreen
AAN-5 Demo Kit Drives VGA Over 300m of CAT5
Figure 10: CEB500 - Top Silkscreen
©2008-2013 Exar Corporation 12/13
Rev 1A
Analog Application Note
AAN-5 Demo Kit Drives VGA Over 300m of CAT5
Rev 1A
For Further Assistance:
Exar Corporation Headquarters and Sales Offices
48720 Kato Road
Tel.: +1 (510) 668-7000
Fremont, CA 94538 - USA
Fax: +1 (510) 668-7001
www.exar.com
NOTICE
EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any
circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration
purposes and may vary depending upon a user’s specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies.
EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or
to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage
has been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances.
Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.
©2008-2013 Exar Corporation 13/13
Rev 1A