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Guidance regarding AD5272 POT controlling gain

Question asked by m3atwad on Jun 30, 2014
Latest reply on Jul 24, 2014 by m3atwad

Hello,

 

I am looking for some guidance as I'm not an expert analog or filter designer.  I am designing a device that will sample sensors that may have very small sensor outputs.  I need a input filter on my device as well as the ability to increase gain before these signals get to my ADC.  All of this will be running off of my products 3.3V VCC rails.  I've used Analog device's online filter design wizard that gave me two a four pole sallen key filter (two sallen key filters yielding -60db/decade).  After the inputs go through these filters I then need to be able to increase/decrease the gain and so I figured the easiest way is to add a non-inverting amplifier after these sallen key filters.

 

So, with this plan I found the AD5272 and thought I could use that to control one of the feedback resistors and therefore control my gain into the ADC within my VCC (3.3V) range.  Effectively I am hoping to plug in this sallen key design from the wizard, connect that output to the input of a basic non inverting op-amp configuration (all op amps I'm using are of the type ADA4661) and have one of the feedback resistors be a POT/Rheostat (AD5272) which I can control through my programmable logic device.

 

Here are some of the schematics.

 

sallenKeyDesign.jpg

 

 

Here is a quick schematic to help show what I'm thinking regarding the AD5272.  Basically I figured the easiest way ( and cheapest) to go about this was to use a single op amp non inverting configuration and a digital pot to allow me to control the gain from my microcontroller.

 

IMG_0001.jpg

 

 

Does this sound like a good idea?  Possible? Reliable? Need some feedback...

 

 

Thanks,

Rob

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