Inverting and Non-Inverting Gain Circuits
Inverting amplifier
The signal enters through RIN; RF returns output to the summing node. The minus sign indicates inversion.
Non-inverting amplifier
The signal drives the non-inverting input directly, so input impedance can be extremely high.
Follower
Connecting output directly to the inverting input gives gain near one and is one of the most useful buffer circuits in electronics.
Bias-current balancing
With bipolar-input amplifiers, resistance seen by each input can be balanced so input bias currents create more nearly equal voltage errors.
Noise gain
The op-amp's own input error sees a closed-loop gain that may differ from the desired signal gain. This noise gain controls bandwidth and stability.
Resistor values
Very low values waste current and load the output. Very high values increase Johnson noise and sensitivity to bias current, leakage, board contamination, and parasitic capacitance.