Method and apparatus for the reduction of phase noise

A method, comprising:

• dividing an oscillating signal having a first frequency according to a sequence of at least three distinct divide ratios to produce a divided signal having a frequency approximating a reference signal frequency;
• and
• adapting said first frequency to reduce a phase difference between said divided signal and said reference signal;
• wherein a next value in said sequence of divide ratios is determined by (a) accumulating an error between a present value in said sequence of divide ratios and an average value of said sequence of divide ratios, (b) accumulating the accumulated errors, and (c) selecting the next value in said sequence of divide ratios such that the multiply-accumulated error is maintained within finite bounds.

A modulator for producing an integer sequence with an average value of N/M, wherein N and M are integers, comprising:

• a first accumulator for accumulating an error between said integer sequence and said average value, N/M;
• a second accumulator for accumulating an error output of said first accumulator;
• and
• a feedback circuit having at least the error output from said first accumulator and an accumulated error output from said second accumulator as inputs for feeding back an accumulated error to the first accumulator for providing a next value in said integer sequence such that the multiply-accumulated error values are maintained within finite bounds.

A method for reducing phase noise, comprising:

• clocking a programmable pre-scaler using the frequency output of a voltage controlled oscillator;
• dividing the frequency output of said voltage controlled oscillator in said pre-scaler using a divide ratio sequence from a modulator to form an approximation frequency that is on average substantially equal to a reference signal, said divide ratio sequence having an average value substantially equal to N/M, wherein N and M are integers;
• comparing the phases of said approximation frequency and said reference signal;
• and
• in response to a difference in phase between said approximation frequency and said reference signal, generating a control signal to adjust the frequency output of said voltage controlled oscillator to correct for the difference;
• wherein only said pre-scaler is required to operate at the full frequency of said voltage controlled oscillator;
• and
• wherein the modulator provides the divide ratio sequence to said pre-scaler to be used for the dividing of the frequency output of said voltage controlled oscillator according to the steps of:
• accumulating an error between said divide ratio sequence and said average value, N/M in a first accumulator;
• accumulating an error output of said first accumulator in a second accumulator;
• and
• feeding back an accumulated error from the outputs of the first and second accumulators to the first accumulator for providing a next value in said sequence of divide ratios such that the multiply-accumulated error values are maintained within finite bounds.