Fractional-N divider, fractional-N phase locked loop and method of dividing a frequency f of an output signal by N, wherein N is a non-integer

摘要

A fractional-N divider for dividing a frequency f of an output signal by N, where N is a non-integer. The fractional-N divider includes an oscillator 209 adapted to provide K output signals I,I=I₁, . . . , I_K. Each output signal I has the same frequency f and period T. The output signals I are mutually phase shifted by T/K or a multiple of T/K. The fractional-N divider further comprises a multiplexer 211 adapted to select one signal from the K output signals I. The selected signal is phase shifted by M*T/K in relation to a previously selected signal, where M is an integer. Additionally, the fractional-N divider comprises a counter 206 adapted to receive said selected signal. The counter 206 is adapted to count a predetermined number X of periods of the selected signal, whereupon the counter 206 outputs a counter signal 230 . The counter 206 is connected to a control input of the multiplexer 211 . The multiplexer 211 is adapted to switch from a currently selected output signal to another selected output signal in response to said counter signal 230.