Why is "input resistance" not described in the operational amplifier data sheets?
The input resistance (Ω) can be calculated as R = V/I per unit voltage (1 V) from the input bias current (A) described in the electrical specifications in the data sheets.
An example using the uPC151 is shown
|Input bias current||-||80||500||nA|
|USB2.0 Host/Peripheral Controller|