Frequency synthesizer having a more versatile and efficient fractional-N control circuit and method

摘要

A frequency synthesizer is provided having a fractional-N control circuit and method that can selectively apply any fractional ratio to a frequency divider within the feedback loop of a PLL. A special digital delta-sigma modulator can be implemented as the control circuit and can receive any arbitrary numerator and denominator value, or their arithmetic combination, or a positive and negative vector values used by the modulator to achieve an average fractional division. Both the numerator and denominator (or the positive and negative vectors) can be chosen based on any integer value to achieve a more optimal, higher frequency resolution and efficient fractional-N control circuit and methodology thereof.