This document discusses the basics of differential amplifiers. It defines differential amplifiers as circuits that amplify the difference between two input signals. It describes the differential gain, common mode gain, and common mode rejection ratio of differential amplifiers. It also outlines the four main configurations that differential amplifiers can have: dual input balanced output, dual input unbalanced output, single input balanced output, and single input unbalanced output. The document is intended as an introduction to differential amplifiers.