| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a PLL frequency synthesizer and a communication apparatus using the same which is miniaturizable, facilitates providing requirements for designing a PLL loop on the occasion of switching a target communication apparatus, and outputs a local oscillation signal having characteristics suited to each communication system. <P>SOLUTION: The PLL frequency synthesizer 1 has a PLL loop circuit comprising: a voltage controlled oscillator 2 capable of switching its oscillation frequency to required local oscillation signal frequencies for a plurality of communication systems different in frequency band; a PLL-IC 3 to which a part of an output signal from the oscillator is inputted and which allows a charge pump output current to be switched according to the plurality of communication systems; and a loop filter 4 having a fixed transfer function. The PLL loop circuit is so constituted that the phase of an open loop transfer function ranges between -140° and -130° at a gain crossing frequency, when the charge pump output current to the PLL-IC is switched. <P>COPYRIGHT: (C)2004,JPO |
