The document provides information about differential amplifiers, including: - Differential amplifiers can measure and amplify small signals buried in larger signals by using two input terminals and amplifying the difference between the inputs. - Historically, differential amplifiers were implemented using a long-tailed pair circuit with vacuum tubes. This circuit provides benefits like immunity to component variations and high gain. - The common-mode rejection ratio (CMRR) measures a differential amplifier's ability to reject common-mode signals (signals that appear at both inputs equally) and is important for cancelling interference. Higher CMRR means better common-mode signal rejection. - Connecting the two inputs together and applying a common voltage allows