Changing PGA amplifer reference on the fly under program control

[Anonymous]

Hi Everyone,

   

I am using a pga in my circuits.  Most of the time I operate it at unity gain where it's input is a InsAmp referenced to AGND and the output is sent to an A to D.  However, I need to get an analog signal from a ground referenced RF crystal detector in one situation.  I mux PGA between the InsAmp and the crystal detector.  Unfortunately, I need some gain when measuing the crystal detector, but to really get much gain without driving the PGA to the rail I need a VSS reference when measuring the crystal detector. The rest of the time I want the PGA referenced to AGND.  No driver is provided to switch the PGA amplifier reference dynamically, but it can be set to VSS in the GUI.   I am assuming it can be done dynamically.  Is that true?  Could someone give me a nickel tour on how to do this for a pga placed at ACB01.

   

Thanks,

   

Tim

[ETRO_SSN583]

Look at this register in TRM -

       

[Bob_Marlowe]

The lower two bits in the register PGA_GAIN_CR0 are responsible for selecting the reference. You may set the value programmatically.

       

Bob

[ETRO_SSN583]

CR0 sets the ref point for the feedback R, not the ref input -

       

[Anonymous]

Thanks Bob and Dana.

   

I have a dog and pony tomorrow, and I wanted to be able to claim more resolution than I could get with a straight unity PGA feeding the A to D.  This will allow me to increase my resolution by 2 or 3.

   

Tim

[ETRO_SSN583]

Glad to assist.

       

Regards, Dana.

[Bob_Marlowe]

"I have a dog and pony tomorrow"

   

That seems to be an idiom I've never heard before, what does that mean???

       

Bob

[ETRO_SSN583]

A presentation.

[Bob_Marlowe]

Thanks,Dana!

       

Bob

[ETRO_SSN583]

Glad to assist.

       

Regards, Dana.