We apply the technique of the calculus of stochastic differential equations to the problem of noise in an electronic circuit with positive feedback. We argue that this is a very natural approach to the more general problem of noise in electronic circuits of all types. We apply the standard small-signal analysis to the circuit, incorporating the standard high-frequency small-signal model for the field effect transistor. This allows us to derive a state-variable
model for the system, which is essentially a coupled system of Ordinary Differential Equations. If we then incorporate a standard noise model for the field effect transistor, we obtain a coupled system of Stochastic Differential Equations, or SDEs. We apply the stochastic differential calculus of Ito to this problem and compare
the results with simulations. We examine the dependence of phase-noise on the system parameters. We also simulate the case where the oscillations become large and use this to investigate the limits of the small-signal approximation.