VARACTOR-LESS OSCILLATOR WITH ENHANCED TUNING CAPABILITY

摘要

The present invention relates to a differential oscillator circuit and a method of controlling the frequency of an oscillator signal. An enhanced frequency tuning mechanism is provided for controlling the frequency of the oscillator signal. The frequency tuning mechanism comprises first frequency control circuitry for controlling the threshold voltage of respective load transistors (M3, M4) of the differential oscillator circuit, and second frequency control circuitry for controlling at least one of a common-mode current (I_BIAS) flowing through branches of said differential oscillator circuit, a tail current (I_TUNE) of an additional feedback circuit (M5, M6) cross-coupled between the drains of a differential transistor stage (Ml, M2) of said differential oscillator and respective gates of said load transistors (M3, M4), and a voltage applied at a middle point of a tapped coil of a resonating circuit of the differential oscillator circuit. Thereby, a linear fine tuning characteristic can be obtained, where the tuning mechanism may for example work as a "gear-box" by stepping coarsely with the first frequency control circuitry through fine intervals generated by the second frequency control circuitry.