Patent ID: 7038496

Claim:
A frequency synthesizer, including: an oscillator, which is designed to emit an output signal with an oscillation frequency which is controlled by means of a control signal; and a device for comparison, which is designed to receive a first input signal and a second input signal and to emit the control signal that is representative of a frequency difference between the first and second input signals, the first and second input signals comprising the output signal of the oscillator and a reference signal, respectively, the device including: a phase/frequency comparator, which is designed to receive the first and second input signals and to emit a first regulation signal; a lowpass filter responsive to the first regulation signal to produce a filtered first regulation signal; at least two current sources, each of which is designed to emit a charge current with a value that is variable according to the filtered first regulation signal; and a capacitive element, which is designed to have the charge current pass through it and to generate the control signal; wherein the phase/frequency comparator includes: a flip-flop RS, the inputs of which for setting to one and to zero are piloted respectively by the first and second input signals, and an output of which is designed to emit the control signal; a first and a second detector for active edges of the first and second input signals respectively, the outputs of which are connected to the inputs for setting to one and to zero of the flip-flop RS; and means for re-initialization of the first and second detectors, which are designed to deactivate one or the other of the detectors, when the active edge which it has detected has been taken into account by the flip-flop RS; the phase/frequency comparator being designed such that the first regulation signal comprises a succession of pulses, each of which has a width which is modulated according to the frequency difference which exists between said first and second input signals.