exact value of the differential output impedance of the ADA4938-1 or ADA4938-2

Document created by analog-archivist Employee on Feb 23, 2016
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What is the exact value of the differential output impedance of the ADA4938-1
or ADA4938-2. Is it 2ohm or 5ohm or 20ohm?There are S parameter plots S11 nad
S22 in the datasheet but I don't know to which circuit they apply to or to
which impedance they apply to.

 

The S11 and S22 plots include external resistors, and don’t reflect the
amplifier’s actual intrinsic input and output resistances. The closed-loop
output resistance is very low, so adding external 49.9 ohm resistors makes each
output close to 50 ohms, and the differential output resistance is therefore
close to 100 ohms. The external resistors are therefore the dominant factors
that affect the output match. On the input, the driver is set up for a 50 ohm
input, again using external resistors, and the input match is based on this
configuration.

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