Patent ID: 6518845
Filing Date: 2003-02-11
Classification: H03L,Y10S

Abstract:
A PLL frequency synthesizer circuit comprising:a voltage-controlled oscillator outputting a signal of a frequency controlled by an input voltage of an input signal, the output signal being used for feedback as an internal change signal; a phase comparator detecting a phase difference between the internal change signal and an external reference signal; and a charge pump outputting an output current pulse of a length corresponding to the phase difference to a low-pass filter and providing via the low-pass filter the input signal having the input voltage corresponding to the phase difference to said voltage-controlled oscillator, said charge pump being controlled so that the input voltage of the input signal becomes a voltage for oscillating a lock frequency; and a current-increase control circuit controlling an absolute value of the output current pulse of said charge pump when a changing instruction of the lock frequency is input and/or when a phase inversion of the internal change signal in a locking-up operation is rendered in response to the changing instruction, wherein said current-increase control circuit sets a first value as the absolute value of the output current pulse during a predetermined interval after the locking-up operation is started and sets a second value smaller than said first value as the absolute value of the output current pulse after the predetermined interval has elapsed.