FRACTIONAL-DIVISION FREQUENCY SYNTHESIZER FOR DIGITAL ANGLE-MODULATION

摘要

A FRACTIONAL-DIVISION FREQUENCY SYNTHESIZER FOR DIGITAL ANGLE-MODULATION In order to deliver an angle-modulated output signal as a function of digital information, the frequency synthesizer delivers an output frequency FS = (N + k)FR, where N is the integral part of a number N+k and FR is a reference frequency. Provision is made for a variable oscillator, an oscillator control loop comprising in series a variable-rank divider prepositioned on the division rank N, a phase comparator for receiving the reference frequency and a summing device. The synthesizer further comprises a phase accumulator for performing at the frequency FR modulo-M summation of a number G = k.M applied to its input. The sum and carry outputs of the accumulator are coupled respectively to the summing device in order to deliver a signal for compensating the signal delivered by the phase comparator and to the divider for delivering a control signal at N+1 of the division rank. An adder having one output coupled to the input of the phase accumulator receives a constant number g on one input and a number dg which is representative of the digital information on another input.