Hi,
I am using AD8220 to amplify the output voltage of a Wheatstone bridge (there is only an NTC Thermistor in the bridge).
I want to use the InAmp in single supply operation. The bridge is designed to always provide the positive input voltage to the InAmp
(Vin= (Vin+) - (Vin-) > 0 ).
The question is if it is necessary to connect the REF pin to Vsupply/2 in this case or it can be tied to GND.
Thanks for your help.
Hi Alireza,
I can't open the link to view your schematic. You can use the tool on the menu where you can insert an image on the thread. As I mentioned above, you can tie the REF pin to ground as long as you are sure that your output is within the output range of the device. This is the reason why I ask you to give me your minimum inputs and gain of your circuit so that I can check if you are operating within the output range of the device. Please refer below image for its specification on a single supply operation:
It shows that your output voltage can swing 150 mV from either rail. I also want to mention that output swing can also be affected by the input common mode which you might also consider. There is a discussion of it on this link about how the input common mode limits the output swing of the Inamp.
So if you have 100 mV input signal, G =1 and your ref pins is tied to ground; you will not get accurate results since the part needs a 150 mV headroom from the rail. You can implement several solutions like increase your gain, increase the input voltage, put a reference voltage or have a dual supply.
If this doesn't work, then I am encouraging you to post again your schematic here so that we can check if we are still missing something.
I hope this helps!
Best regards,
Emman
