AD9845A AD9845A: Using the CCDIN with a DC level up to 4.8V

Document created by analog-archivist Employee on Feb 23, 2016
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I have a CMOS image sensor that output a high of 4.8V when exposing...and then
a waveform of 2.4-3.6 for the video. I used the buffer described in the data
sheet, but am a little worried that the Exposure and video will cause problems
for the AD9845 A/D converter. Could someone give me some advice on how to
approach this?


The max i/p range of the signal level before saturation, should be under 1Volt,
refer to the signal waveform at the bottom of page 3 in the AD9845A datasheet.
The i/p DC restore circuit, restores the DC offset to 1.5V to be compatible
with the 3Volt power supply of the AD9845. The CCD interface starts with an
input clamp. As the common-mode level of the image sensor's output signal could
range from 0 V to more than 9 V,  the signal must be ac-coupled to the
AFE(AD9854A). The input clamp restores the dc level of the signal to an optimum
point within the supply range of the AFE.  I expect the circuit on page
20.fig32 to work fine in your application.
For helpful reading refer to the application note "selecting an AFE(analog
front end) for CCD applications" .