A.V. Kononov, D.P. Zarapkin
This paper deals with intrinsic thermal feedback (ITF) in transistor oscillators, and particularly in those of them using bipolar junction transistors. ITF is an inherent property of any semiconductor device as it arises due to all basic material parameters are temperature dependent. The main topics under discussion are ITF impact on oscillator steady-state regime stability and noise.
The usual approach to an oscillator analysis uses the only nonlinear differential equation describing the first harmonic energy balance. But a practical oscillator is controlled with at least two additional feedback loops: one describes its inertial auto-biasing network, another – inertial changes of transistor active zone temperature induced with dissipated power fluctuations. Thus, the oscillator steady-state regime has to appear as a joint solution of the three nonlinear differential equations.
The corresponding analysis reveals conditions when ITF in conjunction with the inertial auto-biasing could upset the steady-state regime stability. The closer an oscillator to a threshold of instability the more noise. In general case ITF acts like some effective built-in filter which colors additionally the noise spectra.