Integrated circuit fm local oscillator with afc control and temperature

Abstract

A FM local oscillator circuit suitable for integrated circuit fabrication, the frequency of which responds to a first current component for reducing frequency drift of a tuned frequency as a function of temperature and to a second current component for providing automatic frequency control of said tuned frequency. The circuit comprises a cross coupled differential pair of transistors, adapted to be coupled to a tuned circuit manually tunable over a given frequency range, which exhibit a negative conductance substantially controlled by said first current component for sustaining oscillations over said given frequency range and which further exhibit a variable capacitance controlled by said second current component for providing electronic fine tuning of the oscillator circuit. The emitters of the differential transistor pair are joined and coupled to first and second current sources, the first of which is temperature compensated for generating said first current component and the second of which is selectively controlled by an AFC control signal for generating said second current component.