Reference oscillator with variable duty cycle, frequency synthesizer and signal receiver with reference oscillator

A reference oscillator for a transmitter and/or a receiver of electromagnetic signals, the reference oscillator being suitable for generating a modified reference signal alternating ON times and OFF times with a predefined duty cycle from a signal supplied by a reference resonator, wherein the reference oscillator comprising:

• an adjustment circuit suitable for adjusting the duty cycle of the modified reference signal according to at least one adjustment parameter so as to minimize at least one higher harmonic component of the modified reference signal, injected parasitically into a spectrum of electromagnetic signals, and
• a reference generator coupled to the resonator for producing an initial reference signal, the adjustment circuit being coupled to the reference generator for generating the modified reference signal with a predefined duty cycle from the initial reference signal,
• wherein the adjustment circuit generating the modified reference signal comprises:
• a phase-locked loop or PLL, connected to the reference generator and suitable for producing a signal of frequency n times greater than the frequency fref of the initial reference signal,
• a counter connected to the PLL loop for counting the pulses of the signal produced by the PLL loop,
• a comparator for comparing a number of pulses counted to a predefined value m, and producing an ON signal if the number of pulses counted is less than the predefined value m or an OFF signal otherwise, and
• a pulse generator connected to the reference generator and arranged for producing an initializing signal of the same frequency as the initial reference signal, said initializing signal being applied to an initializing input of the counter.