基本反馈理论(Basic feedback theory):In AN165, the ideal op amp was defined. The ideal parameters arenever fully realized but they present a very convenient method forthe preliminary analysis of circuitry. So important are these idealdefinitions that they are repeated here. The ideal amplifierpossesses1. Infinite gain2. Infinite input impedance3. Infinite bandwidth4. Zero output impedanceFrom these definitions two important theorems are developed.1. No current flows into or out of the input terminals.2. When negative feedback is applied, the differential input voltageis reduced to zero.Keeping these rules in mind, the basic concept of feedback can be explored.