AUTOMATIC TUNING OF AN INTEGRATED OSCILLATOR

摘要

According to the invention, when seeking loop locking the control variable (S1) arriving from the loop filter (54) is not admitted as such to the oscillator's (55) control input, but it is attenuated so that it will vary within a small range at the middle of its range of variation. At the same time, the loop's output frequency (fVCO) is compared to the frequency of an external frequency source (53), which is sufficiently close to the nominal frequency of the input signal. When the regulating element finds that the oscillator's output frequency is not in a predetermined frequency window, it will add to or reduce the additional control (VCO Cntrl) which it supplies to the oscillator's control input. When the oscillator's (55) frequency has entered the frequency window, the additional control is frozen and the attenuation is removed from the control variable (S1) arriving from the loop's phase comparator. The loop will thus perform phase locking very quickly to the loop's input signal and, in addition, the locking takes place in the middle of the oscillator's range of regulation.