The datasheet of this opamp says the input impedance is typically 100Meg. So I expect the voltage gain to be halved with a source resistance of 100Meg. But the following simulation doesn't reveal that and gain almost doesn't change:
Above the voltage gain is two. Applied input is 1V. So with a 100Meg source resistance I was expecting 1V output(half of the gain). But the plots show the gain is not affected from the source impedance and is still two.
Why 100Meg source impedance is not halving the output gain if the opamp input impedance is 100Meg?