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How to match the dc common voltage between ADL5385 and ADRF6516

Question asked by plkmn3 on Oct 12, 2013
Latest reply on Oct 15, 2013 by jdobler

Hi;

 

We need help!

We want to use ADRF6516 as the anti-aliasing filter, we have a ADL5385 as a modulator, but the DC common level is 0.5V, ADRF6516's 1.65V.

Somebody suggeted using AC coupling to avoid this conflict,  we tried but failed. The reason seemed to be in AC coupling mode, there is a minute low frequency level drift which cannot be cancel out by our DC Canceller, especially in higher order QAM mode.

Now we want to use a OP, like ADA4930, as a level shift. But the low limit common voltage of it is 0.8V, so we are going to set the level to 1.0V, and use a 2:1 resistor divider to reduce this level to 0.5VDC. Does this will work?

And how high is the input resistor of ADL5385's Baseband ports?

Attached is our schem.

 

Thanks!

 

Donald

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