Electronic Components Datasheet Search |
|
AD8185 Datasheet(PDF) 11 Page - Analog Devices |
|
AD8185 Datasheet(HTML) 11 Page - Analog Devices |
11 / 16 page REV. 0 AD8183/AD8185 –11– Third, the additional power and ground pins also yield lower impedance on the power and ground lines, and therefore minimize the effects of shared impedances on crosstalk. Signal routing is also important for keeping crosstalk low. Shielding and separation should be used for signals that must run parallel over some length on the PC board. If signals must cross, the trace widths should be kept narrow, and the signals should cross at right angles to minimize the capacitance between the traces. 4:1 RGB Multiplexer For selecting among four RGB sources to drive a monitor, two AD8185s can be combined to make a 4:1 RGB multiplexer. A circuit for this is shown in Figure 40. Each RGB source is con- nected to either the three “A” or “B” inputs of one of the AD8185s. In addition, all R signals are tied to “0” inputs, all G signals are tied to “1” inputs, and all B signals are tied to “2” inputs. All of these input signals should be terminated with the standard 75 Ω to ground very close to the IC pins. Each of the outputs of the AD8185 has a series 75 Ω resistor to provide a back termination for the monitor load. Whichever device is selected will drive the output signal through its three termination resistors. When terminated by the monitor, the voltage of these signals will be attenuated by a factor of two. This is normalized by the gain-of-two of the AD8185. Unlike many gain-of-two circuits, the impedance of the AD8185 is very high when it is disabled. This is due to a proprietary circuit that disconnects the feedback network from a low imped- ance when the part is disabled. OE OE OE OE OE OE OUT0 OUT1 OUT2 75 75 75 BLUE GREEN RED TO MONITOR 75 75 75 75 75 75 R G B SOURCE 0 R G B SOURCE 1 75 75 75 75 75 75 R G B SOURCE 2 R G B SOURCE 3 SEL 0 SEL 1 OE SEL A/B IN2B IN2A IN1B IN1A IN0B IN0A OE SEL A/B IN2B IN2A IN1B IN1A IN0B IN0A OUT0 OUT1 OUT2 75 75 75 200 100pF 200 100pF Figure 40. 4:1 RGB Multiplexer Two control bits are required to select the input source for the RGB signals. One is applied to each of the SEL A/B inputs of each device to select between the two input sources for that device. The other bit controls the OE inputs of the two devices. A delay circuit is provided for each device to ensure that the outputs of one device are disabled before the outputs of the other are enabled. If the RGB signals contain the sync information, such as a sync- on-Green, this circuit is all that is necessary for the full 4:1 RGB mux. However, if sync is carried on separate signals, such as in PCs, the sync signals can be multiplexed through a digital multi- plexer that operates from the same SEL signals. The RC in the OE circuit is to ensure “Break-Before-Make” operation. Using the values shown, a 20 ns time constant is created. This will delay the enabling of the outputs of the new selection until after the other devices’ outputs are disabled. This time can be shortened or eliminated if the system can tolerate the glitches caused by simultaneously enabled outputs. EVALUATION BOARD POWER AND GROUND There are three power supply pins on the board. “VCC” is +5 V analog, “VEE” is –5 V analog, and “DVCC” is +5 V digital. These three power supply pins should be connected to good quality, low noise supplies. If the same ± 5 V power supply is used for both analog and digital, separate cables should be run from the power supply to the evaluation board’s analog and digital power supply pins. Three 10 µF tantalum capacitors (C1–C3) are located under the power connector to decouple the power supplies as they first enter the board. As the three supplies get close to the part, they are again decoupled with 0.1 µF ceramic capacitors (C4–C6). Finally, each power pin of the device is locally decoupled with a 0.01 µF ceramic capacitor (C7–C15). The board has a separate analog and digital ground plane. With the jumper at W5 installed, these two ground planes are tied together on the board. Generally, this jumper should remain installed. INPUTS AND OUTPUTS The evaluation board has been carefully laid out to demonstrate the high speed performance of the device. Optimized for video applications, all signal inputs are terminated with 75 Ω resistors to ground (R1–R6). The three outputs are backterminated with 75 Ω series resistors (R12–R14). Stripline techniques are used to achieve a 75 Ω characteristic impedance on the input and output lines. See Figure 41 for the arrangement of the PCB layers. TOP LAYER 75 SIGNAL LAYER POWER LAYER 50 SIGNAL LAYER 0.005" (127mm) 0.0026" (66mm) 0.0038" (96.5mm) 0.0176" (447mm) 0.028" (711mm) 0.005" (127mm) Figure 41. PCB Dimensions In addition, 75 Ω BNC connectors are used on the six inputs (J1–J6) and three outputs (J7–J9). The connectors are arranged in a crescent around the device. This results in all the input and output signal traces having the same length. Unused regions of the multilayer board are filled up with ground planes. As a |
Similar Part No. - AD8185 |
|
Similar Description - AD8185 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |