Impedance matching when AD9717 or AD9779A interfaced with ADL5375

Document created by analog-archivist Employee on Feb 23, 2016
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Can you confirm why I need to use 500ohm or 50ohm impedance matching for the
AD9717 and AD9779A interfaced to ADL5375.
Sorry for that basic questions, but I am from the digital world.

 

 

Remember, that the AD9717's and AD9779A's output and ADL5375's input
common-mode bias levels are both 500mV and hence do not require voltage
shifting circuitry.

With regards to the AD9717, whose fullscale output current=2mA, then to obtain
500mV bias on the output the voltage can vary from 0 to 1V for single-ended.
Therefore, the corresponding resistance (RBIP, RBIN) = 1V/2mA = 500ohms.

In the case of the AD9779A, the fullscale output current=20mA and to have an
output single-end voltage from 0 to 1V, then the corresponding resistance
(RBIP, RBIN) = 1V/20mA = 50ohms.

Refer to Figure 59 in the ADL5375's RevB datasheet for further details

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