Patent ID: 7024171

Claim:
A frequency synthesizer utilizing fractional-N synthesis, comprising: a phase detector having an input receivable of a reference frequency; a loop filter arranged to filter a control signal generated by the phase detector; a tunable oscillator arranged to receive the filtered control signal from said loop filter and provide an output frequency; an integer divider arranged to receive the output frequency of said oscillator, divide the output frequency by a division control number (N+F) and provide the divided output frequency to said phase detector, the division control number being made up of an integer (N) and a fraction portion (F) separated into at least two different fractions; generating means for generating the fraction portion (F) of the division control number, said generating means comprising at least two sigma-delta converters, each of said sigma delta converters processing a respective one of the at least two fractions, one of said sigma-delta converters processing a smaller fraction being driven at a lower clock rate than one of said sigma-delta converters processing the largest fraction; and a first summer arranged to combine the fraction portion (F) of the division control number generated by said generating means and the integer (N) to form the division control number, said integer divider receiving the division control number from said first summer.