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AD8099 Inverting gains of > -1

Question asked by lidar on Aug 7, 2012
Latest reply on May 6, 2014 by vsluiter

I got Multisim going nicely with 2 cascaded AD8099 X5 gain stages to give me a combined gain of 25 at 287 MHz (wanted 300 MHz but 287 is close enough).

 

Then I got too clever, since I wanted a total gain of -25 rather than +25 (that is inverted output w,.r.t. input) I changed the second stage to inverting configuration. Messed about with the compensation pin components and with the cap across the feedback resistor but nothing I could do would give me anything but an oscillator in that inverting stage. I noted on the data sheet that only inverting circuits shown have a gain of just -1.

 

I am obviously missing something important here. Are inverting stages with a gain > -1 possible?

 

For a gain of -25 do I need to go to 3 stages, that is, 2 off X5 non-inverting followed by a gain of -1 "output" stage?

 

Thanks,

Ian

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