ADV7842 analog input resistances

Question

Hello, 
 
 I saw ADV7842 evaluation board schematic and it uses a combination of 51.1R and 24R resistors. My question is, can I just replace them with a single 75R termination resistor to ground from each analog video signal (composite, component, s-video, rgb, vga...etc)? 
 
 thanks

FormerMember · Accepted Answer

Yes, place 2 resistors close to the connector. Use 50 Ohm traces from there. Don't forget the DC blocking caps. 
 The 25 + 50 to ground will match the 75 Ohm cable. The 7842 input is high impedance so it really doesn't affect the cable. The eval. board works fine up to UXGA60 which is ~154MHz data rate. 
 In general you want to place the 7842 close to the connector too. Don't run it across the board. Although your formats are so slow the whole layout is rather tolerant. Running long distances with poor impedance matching at high pixel rates can cause reflections causing image ghosting. Been there, done that. Copy the eval board. 
 Older designs where based on 75 Ohm PCBs. You'd really need to check the layout to see that it's designed that way.)

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ADV7842 analog input resistances

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