Phase-switched dual-mode counter circuit for a frequency synthesizer

A dual-modulus prescaler circuit, in particular for a frequency synthesizer, said circuit comprising:

• a plurality of asynchronous dividers-by-two connected in series, one of the dividers-by-two a master-slave type, for receiving two input signals in phase opposition, and supplying four phase shifted signals with a relative phase difference of 90°,
• a phase selector unit between two of said dividers-by-two for receiving the four phase shifted signals from a first of the two dividers-by-two which is the master-slave divider and supplying a selected one of the four phase shifted signals to the second of the two dividers-by-two, control signals being supplied to said selector unit in order for it to supply at its output a selected one of the four phase shifted signals in a division period determined as a function of a selected division mode, and
• a control unit for supplying the control signals to the selector unit, said control unit receiving an output signal of one of the dividers-by-two for clocking operations in the control unit and a signal for selecting the mode, said circuit dividing the frequency of at least one high-frequency signal by a first factor in a first selected mode and by a second factor in a second selected mode,
• wherein, in a selected one of the first and second modes, the control unit is adapted to supply control signals to the selector unit so that it effects phase switching in each division period between two selected phase shifted signals, which are approximately of sinusoidal shape, the second phase shifted signal being in phase lead of 90° in relation to the first phase shifted signal.