Frequency synthesizer comprising a tuning indicator

摘要

A frequency synthesizer including an oscillator (1) whose frequency is controlled by a tuning signal (TS), a phase detector (4) and a phase lock loop circuit (5, 6). A tuning indicator (7) has a tolerance on the phase difference between the tuning frequency signal and the reference frequency signal. The phase detector produces a first (PS1) and a second (PS2) phase signal upon leading and lagging, respectively, of the phase between the tuning frequency signal (FT) and a reference frequency signal (FR). The tuning indicator includes delay circuits provided at the input of AND-gates in such manner as to cancel the phase signals (PS1) and (PS2) of a duration less than a predetermined duration, and a register producing a confirmed tuning indication signal (IS) only when the phase signals (PS1) and (PS2) indicate stable tuning during at least two consecutive periods of the reference frequency (FR).