Fractional-N phased-lock-loop (PLL) system

In one general embodiment, a fractional-N phased-lock-loop (PLL) structure comprises a first circuit located on an integrated circuit, where the first circuit includes a voltage controlled oscillator for generating a periodic output signal, a phase detector for controlling the voltage controlled oscillator, a charge pump for modifying an input to the voltage controlled oscillator, a frequency divider in a feedback path for modifying a frequency of the output signal, a first multiplexer, and a first random number generator. The fractional-N phased-lock-loop (PLL) structure further comprises a second circuit including a second multiplexer and a second random number generator, wherein the second circuit is a programmable circuit located off the integrated circuit and coupled to the first circuit. Additional systems and structures are also presented.