Patent ID: 6574288
Filing Date: 2003-06-03
Classification: H03J,H03L

Abstract:
A frequency synthesizer having at least one variable frequency output, the output frequency varying as a capacitance within the synthesizer varies, comprising:a discretely variable capacitance circuit within the frequency synthesizer including a plurality of capacitor circuits having capacitances that may be selectably included within an overall capacitance for the variable capacitance circuit, the capacitances of the plurality of capacitor circuits being weighted with respect to each other by selected amounts; a digital control signal coupled to the discretely variable capacitance circuit, the digital control signal comprising multiple-bits coupled to the plurality of capacitor circuits to select which of the capacitances to include in the overall capacitance of the variable capacitance circuit; and discrete control circuitry coupled to the output frequency and providing the digital control signal as an output, the discrete control circuitry being configured to use a predetermined set of capacitance selection cycles to adjust the output frequency to approximate a desired output frequency by adjusting the bits of the digital control signal depending upon feedback from the output frequency; wherein the capacitance selection cycles are configured to successively add a plurality of different capacitances in a predetermined order and in each of a plurality of cycles to drop an added capacitance if the feedback provides a too slow indication and to keep that same capacitance if the feedback provides a too fast indication.