| 摘要 |
PROBLEM TO BE SOLVED: To provide a miniaturized and inexpensive PLL frequency synthesizer, reducing the number of parts by having one part of a circuit shared by a low- pass filter(LPF) and a voltage controlled oscillator(VCO). SOLUTION: For a VCO 6, the anode of a varactor diode 2 is connected to the high potential side of a resonance circuit 1, the cathode of this varactor diode 2 is connected through a resistor 4 to a BPF 5 and the node of the varactor diode 2 and the resistor 4 is grounded via a capacitor 3. When such a VCO 6 is used, a lag/lead filter is made of the capacitor 3 and the resistor 4. Therefore, the number of lag/lead filters conventionally required for sufficiently removing noises superimposed on a DC voltage outputted from a charge pump output terminal 19 can be reduced by one. |
