A clock frequency modulator for an oscillator having a digital circuit for the generation of a signal modulating the clock frequency, the digital circuit adapted to obtain, from the signal generated by the oscillator, a first pulse signal having a lower frequency than the clock frequency of the oscillator, a digital counter adapted to count the pulses of the first signal and to produce a digital signal and a digital-to-analog converter adapted to convert the digital signal in the signal for modulating the clock frequency of the oscillator.