Contribution to the linear theory of frequency stability of RC oscillators

In this paper, the frequency stability problem in RC oscillators is considered. General expressions describing variations of the real and imaginary parts of the characteristic equation roots, caused by variations in network elements' parameters, are developed. The superiority of our approach over the previously presented ones is that it allows to describe not only slow variations (long-term stability) but also fast variations (short-term stability) of oscillation frequency. It is shown that the so-called frequency stability factor
S_F
can be a reasonable criterion of frequency stability only for some types of RC oscillators. In this context, oscillators with the selective feedback path being of bandpass or bandreject type and with some additional resistive feedback path of the maintaining amplifier are discussed in detail.