With a single-ended op amp, I can create a unity-gain voltage buffer like this:
The input impedance of this circuit is equal to the input impedance of the op amp, which is normally very large.
I'm trying to reuse an existing analog front-end circuit that has a differential input connected to a fully-differential op amp. The op amp is wired to provide gain, similar to this:
I know I can set \$R_f = R_g\$ to get unity gain, but if I understand right, the input impedance of the circuit is \$R_g\$. If I want a differential input impedance on the order of megaohms, is my only choice to put megaohm resistors in this circuit? Or is there some other way to wire it that can take advantage of the naturally high input impedance of the op amp itself?