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AD9826: input common mode range with CCD signal / level shifting

Question asked by fullwell on Oct 12, 2016
Latest reply on Oct 20, 2016 by fullwell

Hello Forum,

 

I want to use the AD9826 for sampling a CCD-signal [1-Channel CDS Mode]  (see attachment).

 

ADC-Settings

- Input Range=4V;

- 1-Channel CDS Mode=VINR

- After C3 (AC Coupling Capacitor [0.1µF] to remove the DC component) the maximum ADC-Input signal is between -0.6V and + 3.2V (see attachment).

 

In my actual understanding of the AD9826 datasheet, the ADC samples between 0V-4V when the Input Range is set to 4V (via Configuration Register).

 

Questions:

 

What happens when the CCD-signal is between -0.6V and 3.2V?

=> Is the AD9826 capable to sample the -0.6V or does the ADC samples only 0V when the input voltage is below 0V?

 

In the datasheet i found only one sentence on page 16:

The bias voltage charges the external 0.1 μF input capacitor, level-shifting the CCD signal into the AD9826’s
input common-mode range.

 

Does it mean that the AD9826 is capable to see/sample voltages below 0V due to the level shifting?

If yes - what is the minimum voltage on VINR?

 

If the AD9826 is not capable to sample the -0.6V:

Is it possible to apply a voltage of -0.6V on the OFFSET-pin to level shift the (-0.6V - 3.2V)  to  (0V - 3.8V)?

 

Would be great to have a fast response on my questions

 

Regards and thanks so far!

Julian

 

P.S. Sorry for my poor english...

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