Abstract: Device for synchronizing two constant high frequency digital pulse sequences S and R.sub.f comprising a first oscillator producing the frequency sequence R.sub.f at the fundamental frequency f and a second oscillator producing the frequency sequence of pulses S also at the frequency f. The second oscillator is a ring oscillator having three loops of inverted logic gates connected in series and corresponding respectively to the frequency f (used if synchronism exists), to a higher frequency f.sub.1 (used if there is a phase lag) and a lower frequency f.sub.2 (used if there is a phase lead) with the choice of the operating loop being made by a multiplexer on the basis of instructions from a phase detector permanently comparing the synchronism, lead or lag state of the sequence S compared with the sequence R.sub.f.