AD8328: input and output coupling

Document created by analog-archivist Employee on Feb 23, 2016
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My customer want to use this AD8328 in MRI, our datasheet only shows one kind
of application circuit, which is AC coupled input and transformer coupled
output, Can we use other kinds of coupled outputs?


The AD8328 is transformer coupled in the application for several reasons.  The
first reason is that the output of the amplifier is biased up to a DC bias
level.  The transformer AC couples the signal so this is not an issue.  The
second reason is that we need to maintain a 75 ohm output impedance in order to
drive CATV systems, a transformer allows us to lower the output impedance (and
lower the apparent gain) of our amplifier.  That being said, if a different
coupling scheme is used, it is important to maintain the first condition if
output impedance is not an issue.  By AC coupling the outputs, you can expect a
300 ohm output impedance, but the part should function (but the typical
performance characteristics may be different).