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Cascading 2 ADRF6516's

Question asked by twlebrecht on Mar 6, 2015
Latest reply on Mar 11, 2015 by jdobler

We recently purchased an ADRF6516 Eval board.  We bench tested and used it in our radar systme as an I/Q amplifier/filter.  It preformed exceptionally.  The only issue we have with it is it does not have quite enough gain for us.  Initially I was just planning on using a few op-amps on the input and output of this device to give us the desired ammount of gain.  Currently we use a 56dB gain stage in this possition and I would like to increase that to roughly 60dB.  The most I am able to get out of the ADRF6516 eval board into a 50ohm load is about 39dB.  I was thinking of maybe just cascading 2 of the ADRF6516s together instead of using an op-amp solution.  It would preserve the excellent I/Q phase matching of the components as well as apply additional filtering.  My A/D can handle up to 2Vpp, so I would adjust the VOCM pin on the second gain stage to maximize my dynamic range, and adjust the VOCM pin on the first gain stage to avoid saturation of the second.  My inputs and outputs to the amplifier circuit are single ended, but I would use a differential interface between the 2 gain stages.

 

Are there any major drawbacks to this approach?

 

Also, I obsereved a 20mV DC offset on teh eval board whenever I had USB connected.  Just thought I would mention it.

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