PLL frequency synthesizer and portable terminal employing the PLL frequency synthesizer

摘要

A PLL frequency synthesizer has: a reference frequency generator which issues a first frequency signal; a PLL section which outputs a phase error signal based on the first frequency signal and a second frequency signal; a first filter which smoothes the phase error signal output from the PLL section according to a first reference, and which outputs a first smoothed phase error signal; a second filter which smoothes the phase error signal output from the PLL section according to a second reference, and which outputs a second smoothed phase error signal; a switch which issues, in a switching mode, the first or second smoothed phase error signal output from the first filter or the second filter; an output frequency generator which issues a second frequency signal based on the first or second smoothed phase error signal to the PLL section; and a switch controller which controls the changeover of the switch.