query about gain equation of AD8351 in datasheet

Document created by analog-archivist Employee on Feb 23, 2016
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The question is, there is a equation in p10 in datasheet. So what is the
meaning about "(5.6)" in the equation, there is also a table lists some
examples .But when I calculate the Av by using above equation, I can not get
the same value as table1.

 

The values (5.6, 9.2, 4.6, 19.5, and 39) are simplified constants.  This
equations is a first order (simplified) equation to give the gain.  Those
constants represent various variable (gain, resistances) that are grouped
together to have a simple formula.  On its own, 5.6 is of little importance.
The Av comes out in unitless gain and needs to be converted to dB to match the
table (20*log Av).  Again, the equation offered is only of first order.  Some
tuning would be required.  I believe the resistor values in the table were
tweaked to get close to called out gain level.

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