ADCMP607 - why example circuits have external 50R pull ups?

Question

Hello, 
 
 Why does the data sheet show internal 50R pullups as part of the CML outputs as shown below:

But in the example circuits each one has external 50R pullups on the output. Are you required to use the external 50Rs? This will be driving 50R transmission lines to another CML input.

Any guidance is greatly appreciated! 
 
 Thanks!

Jvillanu · Accepted Answer

Hi, 
 No need for this pull up if your circuit will be connected to a CML input receiver with an internal pull up of 50 Ohm, and yes it is correct to have a 50ohm line impedance. 
 If in case your CML receiver does not have an internal 50 Ohm pull up, you can use a 50 Ohm pull up near the input of your CML receiver with still, 50Ohms line impedance. 
 Both condition will enable proper line termination. 
 
 Regards, 
 joven)

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ADCMP607 - why example circuits have external 50R pull ups?