Self-excited oscillation refers to the stable and continuous oscillation generated by itself without external excitation signal. If there is no input signal at the input end of the amplifier, there is still an output signal with a certain amplitude and frequency at the output end. This phenomenon is self-excited oscillation.

From a mathematical point of view, self-excited oscillation is a kind of free oscillation that appears in some nonlinear systems. A typical example is the system described by Vanderbilt equation, and the equation form is MX-f (1-x2) x-kx = 0 (m >; 0，f & gt0，k & gt0)。 Where x and x are the first and second derivatives of the variable x, the analysis shows that when the value of x is small, the damping f is negative, so the motion diverges; When the value of x is large, the damping f is positive, so the motion is attenuated. Therefore, regardless of the initial conditions, the motion of the system tends to be a continuous oscillation, that is, self-excited oscillation.