High Quality Content by WIKIPEDIA articles! An operational amplifier, which is often called an op-amp, is a DC-coupled high-gain electronic voltage amplifier with differential inputs and, usually, a single output. Typically the op-amp's very large gain is controlled by negative feedback, which largely determines the magnitude of its output voltage gain in amplifier applications, or the transfer function require. Without negative feedback, and perhaps with positive feedback for regeneration, an op-amp essentially acts as a comparator. High input impedance at the input terminals and low output impedance are important typical characteristics.