| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a PLL synthesizer circuit which improves S/N characteristics by controlling a crossover frequency in AM reception and FM reception. <P>SOLUTION: The present invention relates to the PLL synthesizer circuit for an AM/FM receiver comprising: a phase comparator circuit which generates a phase difference signal in accordance with a phase difference between a reference signal and a frequency-divided signal frequency-dividing an output signal of the PLL synthesizer circuit; a charge pump circuit which performs current control based on the phase difference signal and generates a charge pump signal while switching the current control in use for AM and in use for FM; a register circuit for switching the current control of the charge pump circuit in use for AM and in use for FM; a VCO circuit which inputs the charge pump signal, smoothes the charge pump signal, oscillates at a frequency corresponding to a control voltage signal as a control voltage and outputs a local oscillation signal; and a frequency divider circuit which frequency-divides the local oscillation signal and outputs a result as the frequency-divided signal. <P>COPYRIGHT: (C)2008,JPO&INPIT |
