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questions about AD8351 output common voltage adjustment

Question asked by blank on Aug 24, 2011
Latest reply on Aug 29, 2011 by blank

I use two AD8351 and an AD8370 in series before an ADC to amplifier weak signals from DC to about 100MHz.

Now there has a problem:I can not adjust the output common voltage of AD8351.

 

I use 3.3V for AD8370 and the ADC so I want to adjust the last ad8351 output common voltage to about 3.3/2~1.65V.

The output common voltage notes form the ad8351 datasheet: output HI/LO, biased to VOCM.

About VOCM: voltage applied to this in sets the common-mode voltage at both the input and output.

 

I followed the fig.2 in the datasheet, and I have already managed to change the PIN10 (VCOM) to about 1.65V.  But during the VOCM voltage adjustment, the output common voltage stay at the same level and doesn’t change a bit……

Is there any misunderstanding above?

I wondering that if I can not adjust it at last maybe I have to change all the power supplies of the AMPs to 3.3V….

 

Thanks a lot!!

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