Are the 33 Ohm Resistors on the TTL output of the ADI video decoder needed?

Question

In the recommended schematic for the ADV7180, ADV7182, ADV7280, ADV7281, ADV7282, ADV7283 the TTL output pins have 33 Ohm series resistors ? Why are these needed ?

ADIApproved · Accepted Answer

The 33 Ohm series resistors combine with the internal resistance of the video decoder to provide a 50 Ohm source termination for the TTL lines. This resistance prevent impedance discontinuances and prevents reflections on the TTL PCB traces. 
 The LLC pin is the highest frequency output pin so it has the greatest need for source termination. 
 The 33 Ohm series resistors should be places as close as possible to the video decoder and on the same side of the PCB as the video decoder.

The 33 Ohm series resistors may not be needed if the PCB traces are very short. However great care must be taken in the layout of the board to minimize reflections. 
 The 33 Ohm series resistors also help reduce the EMI field generated by the TTL outputs from the video decoders by slowing the rise/fall times. 
 
 regards, 
 Robert Hinchy 
 Senior Applications Engineer, 
 Analog Devices Inc.)

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Thread Details

Are the 33 Ohm Resistors on the TTL output of the ADI video decoder needed?