Patent ID: 7834705
Filing Date: 2010-11-16
Classification: H03L

Abstract:
1. A frequency synthesizer comprising: a multi-band voltage controlled oscillator comprising a plurality of voltage controlled oscillating cores outputting oscillation frequencies having different bands according to an input control voltage, the plurality of voltage controlled oscillating cores outputting a frequency band divided into a plurality of bands, each voltage controlled oscillating core outputting one of said divided bands, one of the voltage controlled oscillating cores operating in one of the bands according to the control voltage; a comparator unit comparing the control voltage with a pre-set reference voltage range; and an oscillation band-determining unit changing the band where the voltage controlled oscillating core operates into another one of the bands when the control voltage is out of the pre-set reference voltage range, wherein the oscillation band-determining unit comprises, an up/down counter generating an up-count signal when the control voltage is greater than the maximum value of the reference voltage range, and generating a down-count signal when the control voltage is less than the minimum value of the reference voltage range; a first lookup table storing information about the respective bands corresponding to the plurality of voltage controlled oscillating cores and information about bias currents provided to the plurality of voltage controlled oscillating cores by each of the bands; a bias current-supplying unit, when the up-count signal is generated, providing the relevant voltage controlled oscillating core with the bias current corresponding to a high frequency band among the bands adjacent to the band where the voltage controlled oscillating core is operating, by referring to the first lookup table, the bias current-supplying unit, when the down-count signal is generated, providing the relevant voltage controlled oscillating core with the bias current corresponding to a low frequency band among the bands adjacent to the band where the voltage controlled oscillating core is operating, by referring to the first lookup table; and a prescaler converting the oscillation frequencies output from the voltage controlled oscillator through a prescale operation, the prescaler having a plurality of different operation bands according to the oscillation frequencies, wherein the oscillation band-determining unit further comprises a second lookup table storing information about the operation band of the prescaler corresponding to the frequency band that each of the voltage controlled oscillating cores has, and when the up-count signal is generated, the prescaler changes the operation band into the operation band corresponding to a high frequency band among the bands adjacent to the band where the voltage controlled oscillating core is operating, by referring to the second lookup table, and when the down-count signal is generated, the prescaler changes the operation band into the operation band corresponding to a low frequency band among the bands adjacent to the band, where the voltage controlled oscillating core is operating, by referring to the second lookup table.