An opamp amplifies the voltage difference between the two input pins.
Ideally the gain is infinite, the offset voltage is zero, the inputs
draw no current and introduce no noise. Circuit behaviour is
defined by passive components which are used to set feedback from
the output to the input. One of the simplest circuits is the
non-inverting amplifier where the gain is set by the passive
components, ZF and ZG.
The simplest analysis, assuming an ideal opamp, will yield the result that Vout = Vin * (ZF + ZG) / ZG.
The ideal valid range of common mode
signals has no limits, and the device tolerates infinite differential
voltages. Input characteristics can be grouped into voltage and current specifications.
The output needs to be able to drive the feedback network and the load without difficulty.