Operational Amplifier Fundamentals Unit 3 – The Noninverting Amplifier
Due to the very high input impedance of the op amp, a resistor (RIN) is usually connected
between the positive terminal and circuit common. RIN prevents op amp saturation should the
circuit input voltage (VI) be disconnected (referred to as a floating input). The input impedance
of the circuit shown essentially equals the ohmic value of RIN.
A noninverting op amp displays all the attributes of op amps in general: high input impedance,
low output impedance, and high gain.
The circuit input voltage is applied to the positive op amp input. This means that the circuit
summing junction is not at virtual ground but at a potential required to hold the differential input
voltage (VD) at 0V.
To determine the circuit current distribution, apply Ohm's law.
NOTE: VRIN is the same as VI, VR4 is the same as VO, and R1 and R2 form a voltage divider.