Barkhausen criterion

(electronics) A criterion used to determine the stability of an oscillator circuit which states that, if the circuit is seen as a loop consisting of an amplifier with gain A and a linear circuit whose gain β(jω) depends on frequency ω, then the loop will oscillate with a perfect sine wave at some frequency ω₀ if at that frequency Aβ(jω₀) = 1 exactly, that is, if the magnitude of Aβ(jω₀) is exactly 1 and its phase is 0° or 360°.