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AD5791 Noise?

When operating the AD5791 in the Gain of Two Configuration see Page 26
Datasheet, rev. C) when
VREFP = 10V
VREFN = 0V
AD8676 and AD8675
the measure noise is about 30 nV/Hz^0.5 at 1 kHz at Midscale (0V Out).
This is much more than the specified 7.5 nV/Hz^0.5 at Page 3.

Is this because of the high noise level of the internal Amplifier A1? I
didnt find anything in the datasheet or in the appnotes about noise of A1.

 

see the top header conditions just above table 3.

using Fig 54 configuration the gains is now 2. The DAC noise is inherit a gain
of two also. and that there are noise factors being introduced by A1 and the
external buffers (if one have it). plus noise from all these R1, Rfb, Rfb from
the A1 paths.

In addition noise is a function of temperature. Other contribution factors are,
the layout, track and interference, psu, not to mention the measuring
instruments spec/accuracy and the calibration factor from the equipment itself.
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