AAN-5 Demo Kit Drives VGA Over 300m of CAT5

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AAN-5 Demo Kit Drives VGA Over 300m of CAT5 Introduction Due to its low cost, wide availability and predictable electrical characteristics, standard un-shielded CAT5 twisted-pair interconnect is a

1 AAN-5 Demo Kit Drives VGA Over 300m of CAT5 Introduction 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 V SYNC and H SYNC over twisted pair solution that will handle VGA (640x480) and SVGA (800x600) formats. (A solution for VGA (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 CEB Encoder (single to differential driver) that encodes the five single-ended data lines (R, G, B, V SYNC, and H SYNC ) 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, V SYNC, and H SYNC. VGA DSUB Connector from Computer CEB Transmitter Board R G B V SYNC H SYNC GND ENCODER Single-ended to differential RGB & V SYNC / H SYNC CEB501 Receiver Board DECODER Differential to single-ended RGB & V SYNC / H SYNC R G B V SYNC H SYNC GND VGA DSUB Connector to Monitor 0-300m CAT5 Cable Figure 1: Demo Kit Block Diagram Exar Corporation Kato Road, Fremont CA 94538, USA Tel Fax

2 Basic CAT5 Information 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. 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. Basic VGA Information 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 VGA (1024x768) format is in development) Schematic Discussion: Transmitter Board - CEB The CEB 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 CEB. It consists of a power supply voltage regulator, three single to differential cable driver circuits (RED, GREEN, BLUE video), a H SYNC and V SYNC encoder block, and a common-mode voltage generator. The CEB 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. V SYNC and H SYNC are expected to be standard logic levels. The circuit creates the following weighting table for the 4 possible combinations of V SYNC and H SYNC. 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. Hsync Vsync RED CM Green CM BLUE CM Low High Low Low High Low High High 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 (H SYNC ) and vertical (V SYNC ) pulses. To run the 5 separate video information signals over three channels, Exar s driver/receiver solution encodes the H SYNC and V SYNC 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 H SYNC and V SYNC information Exar Corporation 2/13 Rev 1A

3 R RP G B 225 RSYNC 225 VSYNC RN GP GN BP BN VSYNB HSYNCB k VSYNB VSYNC RSYNC k To all ESD Diodes HSYNCB SD Vout To Circuit Power HSYNC ADJ Figure 2: CEB Transmitter/Encoder Schematic Exar Corporation 3/13 Rev 1A

4 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 CLC0. The dual CLC0 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 Ω resistors (i.e. R7 and R8 in figure 3, etc.). The Ω resistor is used to set the DC bias condition to the generated V REF level (2.5V) as well as to set the input impedance to Ω. The net input impedance is the Ω resistor in parallel with the 255Ω impedance of the inverting amplifier. Green channel receives V SYNC 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 Ω 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 R C1 channels except that it contains two common-mode inputs. This allows for the VSYNCB and HSYNCB summing operation to provide the desired weighting. 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 CLC5 amplifiers are required for these functions due to their rail to rail output capability. U2-A R5 RP R3 R11 RSYNC R7 R R4 649 R8 R2 R1 RN U2-B R6 Figure 3: RED Channel Schematic Exar Corporation 4/13 Rev 1A

5 G C4 GP B R12 C6 R22 U1-A R16 R14 VSYNC R13 R17 R R R9 U1-B Figure 4: GREEN Channel Schematic VSYNCB 150 R31 R23 HSYNCB 150 R U3-A R26 R24 R27 R25 R19 R20 R29 GN BP 255 R21 BN R30 U3-B Figure 5: BLUE Channel Schematic Exar Corporation 5/13 Rev 1A

6 R40 R41 C7 R36 R38 R37 VSYNC R50 R32 R34 R33 HSYNC R49 U5-B k R39 U4-A k R35 U4-B VSYNCB HSYNCB R45 R44 R43 U5-A R42 RSYNC Figure 6: Transmit Common-Mode Sync Control with Common-Mode Reference Generator Exar Corporation 6/13 Rev 1A

7 Schematic Discussion: 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 H SYNC and V SYNC decoder and driver block and a common-mode voltage generator. As with the CEB, 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 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 V SYNC 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. One of the two CLC0 amplifiers performs differential to single ended conversion, while the second performs both the DC boost and high frequency equalization function. 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. 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 Ω for proper driving a doubly-terminated video load. Cable Length (meters) DIP Switch Position to 150 OFF ON OFF OFF 151 to OFF OFF ON OFF 201 to 300 OFF OFF OFF ON Table 2: Suggested DIP Switch Settings for Various Cable Lengths RP R1 R n C1 R7 R8 R6 R2 R4 56 R5 RN 255 R9 255 R R10 RBCM GP same circuit as red R27 G 4 GN BP same circuit as red 0p 330p B p 470p BN 250 RBCM 330p 47p p 22p 499 Figure 7: RED, GREEN, and BLUE Cable Equalizer Schematic Exar Corporation 7/13 Rev 1A

8 Figure 8 details the receiver support circuitry. It uses three low-cost, rail to rail output CLC5 dual amplifiers. One half (single amplifier) of a CLC5 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 10k R93 R94 C38 U8-B RBCM R85 R92 U10-A resistor.) 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. G U10-B R90 VSYNC R88 B R uF U8-A R86 HSYNC U9-B R91 VCVR R87 U9-A Figure 8: Adjustable Receiver Schematic Exar Corporation 8/13 Rev 1A

9 Analog Application Note RBCM To all ESD Diodes RP n SD Vout To Circuit Power 56 RN 255 ADJ R 255 same circuit as red GP R G GN p 330p 620 BP same circuit as red 250 BN B p 470p 330p 47p k p 22p Same as Red Channel 10k G Same as Red Channel B RBCM VSYNC G B uF HSYNC R Figure 9: CEB501 Receiver/Decoder/Equalizer Schematic Exar Corporation 9/13 Rev 1A

10 Set-Up and Operation 1. Before starting, connect the remote monitor directly to the VGA output on the back of the PC. For Windows-P 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 (VGA) 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 CEB transmitter board. 4. Choose the desired CAT5 cable length and connect the CEB to the CEB501 through the modular RJ45 connectors. 5. Based upon the length of the CAT5 cable, use Table 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. 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 CEB, 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. 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 Exar Corporation 10/13 Rev 1A

11 Bill of Materials Item Manufacturer Manufacturer P/N Description Qty on CEB Qty on CEB501 1 Circuits West CEB Printed Circuit Board Circuits West CEB501 Printed Circuit Board Exar CLC0 Dual OP-Amp Exar CLC5 Dual OP-Amp CTS POS SPST Dip Switch Tyco P DSUB Connector EDAC A RJ45 Modular Jack Diodes Inc. SDA004-7 Dual Schottky Barrier Diodes Inc. 1N4148-T 1N4148 ESD Diode MicroChip MCP1825-ADJE/AT ma LDO Panasonic 24.9 Ω Resistor Panasonic Ω Resistor Panasonic 56.2 Ω Resistor Panasonic Ω Resistor Panasonic Ω Resistor Panasonic 150 Ω Resistor Panasonic Ω Resistor Panasonic 249 Ω Resistor Panasonic 255 Ω Resistor Panasonic 280 Ω Resistor Panasonic 300 Ω Resistor Panasonic 4 Ω Resistor Panasonic 499 Ω Resistor Panasonic Ω Resistor Panasonic 523 Ω Resistor Panasonic 549 Ω Resistor Panasonic 649 Ω Resistor Panasonic 1 kω Resistor Panasonic 2 kω Resistor Panasonic 2.26 kω Resistor Panasonic 10 kω Resistor Panasonic kω Resistor Panasonic 107 kω Resistor Panasonic 22 pf Capacitor Panasonic 47 pf Capacitor Panasonic pf Capacitor Panasonic 147pF Capacitor Panasonic 330 pf Capacitor Panasonic 470 pf Capacitor Panasonic 0 pf Capacitor Panasonic 0.1 uf Capacitor AV 6.8 uf Capacitor AV 220 uf Capacitor Exar Corporation 11/13 Rev 1A

12 Figure 10: CEB - Top Silkscreen Figure 12: CEB - Top View Figure 11: CEB501 - Top Silkscreen Figure 13: CEB501 - Top View Figure 14: CEB - Bottom Silkscreen Figure 15: CEB501 - Bottom Silkscreen Figure 16: CEB - Bottom View Figure 17: CEB501 - Bottom View Exar Corporation 12/13 Rev 1A

13 For Further Assistance: Exar Corporation Headquarters and Sales Offices Kato Road Tel.: +1 () Fremont, CA USA Fax: +1 () NOTICE EAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EAR 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. EAR 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 EAR 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 EAR Corporation is adequately protected under the circumstances. Reproduction, in part or whole, without the prior written consent of EAR Corporation is prohibited Exar Corporation 13/13 Rev 1A

XRT6164A Digital Line Interface Transceiver

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