Full scale input range and offset adjustment range

Document created by analog-archivist Employee on Feb 23, 2016
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The full scale input range (valid input maximum minus valid input minimum) on
the AD9884A is guaranteed to be adjustable from 0.5V to 1.0V (gain adjust). It
is typically adjustable from 0.45V to 1.10V. This means that with the offset
adjustment centered, the typically minimum and maximum valid input levels will
be 0.0V and 0.45V with the gain register set to 0, and 0.0V and 1.10V with the
gain register set to 255.

The offset adjustment range is typically 23.5% of full scale input range. If we
consider the effect of the offset adjustment, the actual minimum and maximum
valid input levels (voltage level input for output code 00 and voltage level
input for output code 255) would typically be:

With gain at 0 and offset at minimum [ -0.106V and 0.344V]
With gain at 0 and offset at maximum [ 0.106V and 0.556V]
With gain at 255 and offset at minimum [ -0.26V and 0.84V]
With gain at 255 and offset at maximum [ 0.26V and 1.36V]

If Echostar needs the span of the input (valid input maximum minus valid input
minimum) to be adjustable from .45V to 1.2V, then the typical AD9884A will not
meet this requirement. "Close but no cigar."

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