Hi Matt, ^_^~
I also want to ask questions about AD8221 here. Actually I built a very simple circuit with it, just as Figure 47 in AD8221 Datasheet (rev.C). I use 500ohm as Rg, +-15V as Power Supply, with 0.1uF capacitor on each power supply pin to REF, REF is connected to ground, load is 10kohm. I just wanted to test this circuit but encountered problems.
My input is generated by a TEKRONIX Signal Generator, and its negative polar is connected to ground. Input range is 10mV to 100mV, f is DC to 1kHz. But no matter which signal I tried, the output stayed on zero all the time! No Output...By the way, I use non-isolation oscilliscope to observe the curve, so -IN and REF can be viewed as tied together. I really don't know the reason...do I need some special measure instruments, like isolation probe, to observe circuits with AD8221 ?
Another question is, must the REF to be tied with the middle point of the Power Supply (I mean the 0V point) ? If not, what is the range of their difference? REF can be maximum as +Vs and Minimum as -Vs ?
Hope you can help me with that.