Patent ID: 6628172
Filing Date: 2003-09-30
Classification: H03L

Abstract:
A frequency synthesizer which functions according to the principle of fractional frequency synthesis, comprising:a phase-regulated oscillator (1), a phase detector (2), a reference frequency source (5), a frequency divider (3) which can be adjusted to an integral division ratio (N), an adjusting device (6) in which a desired fractional rational division ratio (P, F) of the frequency divider (3) is adjustable as a digital value, and a control circuit (7) including an integrator, the output of which is a correction value (K) that is added to an integral component (P) of the desired fractional division ratio (P, F) so as to produce a corrected output value (9), the integral division ratio (N) of the frequency divider (3) being controlled with the corrected output value (9) in such a way that a fractional division ratio corresponding to a fractional component (F) of a desired division ratio is simulated and a phase noise of the output frequency close to a carrier, resulting from a periodic changeover of a division ratio, is simultaneously reduced, characterized in that a first-order or higher-order IIR low-pass filter is used as an integrator, of an integrated value produced at an output of the IIR filter, the integral component is reinjected to an input (10) of the low-pass filter and provided as the correction value (K) and a difference between the correction value (K) and the fractional component (F) is delivered to a first register (12) of the IIR low-pass filter.