| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a frequency synthesizer corresponding to multimode which carries out the optimization of a consumption current in all modes, and suppresses enlargement of a chip area. <P>SOLUTION: The synthesizer is provided with a VCO (voltage controlled oscillator) 6, a variable frequency divider which divides a frequency of an output signal of the VCO, a phase comparator 3c which compares phases of the output signal of the variable frequency divider and a reference signal, a charge pump 4c whose charge and discharge outputs are controlled based on an output signal of the phase comparator, and a low pass filter which obtains an average of output signals of the charge pump, and supplies to the VCO as control voltage. The variable frequency divider is configured to count output of a modulus prescaler by a programmable counter, controls a frequency dividing ratio of the modulus prescaler based on the count value, and establishes a frequency dividing ratio from a fraction frequency dividing control unit. The synthesizer is composed to be provided with a plurality of modulus prescalers whose composition is different, and composes frequency synthesizers whose phase comparison frequencies are different by switching the modulus prescalers to the same output frequencies of the VCO. <P>COPYRIGHT: (C)2008,JPO&INPIT |
