AD9245_differential input configuration with AD8351

Document created by analog-archivist Employee on Feb 23, 2016
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the figure 40 in the datasheet of AD9245  is similar with the EVB (schematic in
figure 49,50).  The output common-mode voltage of the AD8351 is set to AVDD/2
(VAMP/2 in EVB), AV coupling with AD9245. In the EVB schematic the VIN+ and
VIN- are set to AVDD/2. But in figure 40 there is no such setting. So I'm a
little confused.


The application schematic  showing the AD8351should DC couple the output of the
AD8351 (i.e. remove DC block caps) since its output is biased to AVDD/2 and the
AD9245 should have it inputs biased at AVDD/2. 
For AC coupled applications, one must use an extra bias circuit to establish
the dc common-mode for the ADC as shown in figure 41 (via transformer
center-tap) or 42 (via resistor network).