AD9742_several questions_differential resistor

Document created by analog-archivist Employee on Feb 23, 2016
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The question is about the differential resistor in Figure 31.
Is the ratio of Rdiff : Rload should be same with the ratio of transformer's
impedance.
The circuit will work normally if we do not add Rdiff but will make the VSWR
higher. Is that right?

 

The resistance presented in the schematic you attached, will be Rload/2 if
RDIFF and Rload are the same values. The idea of Rdiff is to present an
impedance close to the part that will assure good termination and another one
far away but where you do not have to be as careful for line impedance
matching. Removing RDIFF is not recommended for this reason without it you will
have to be careful of the impedance you are presenting at the pin level and it
is risky with a transformer (not the most stable in term of impedance over
frequency).

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