An5: Demo Kit Drives Vga Over 300m Of Cat5

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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