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DC-Coupled AD8310 Output

Question asked by mtapalla on Sep 19, 2011
Latest reply on Sep 20, 2011 by mtapalla

Hello!

 

I have the AD8310 setup in the DC-coupling configuration as shown in Figure 38, with the corresponding transfer function in Figure 39, both reproduced below:

 

However, I have a "dirty" output. This is the transfer function I am seeing, without a filtering capacitor on the BFIN pin:

 

The datasheet states the nominal 25 MHz output video bandwidth can be reduced by connecting a ground-referenced capacitor (CFILT) to the BFIN pin. Also, the video bandwidth should typically be set at 1/10th the frequency of the minimum input frequency. My minimum input frequency is 300 kHz, so my video bandwidth is 1/10th of that, or 30 kHz. I plug it into equation 11 of the datasheet, and thus this gives me a CFILT of about 1800pF. This is my transfer function after attaching a 1800pF cap on BFIN:

 

 

The result is not that much better, and I lose a bit of that dynamic range below 1mV. Any suggestions how I can reduce the ripple on my transfer function, without compromising my dynamic range?

 

Thank you for your time!

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