| 摘要 |
PURPOSE: To build an LPF into an IC in order to decrease the number of component parts of a PLL circuit by using as the ON resistance of a transistor constructing a charge pump and as the resistance of the LPF. CONSTITUTION: A phase comparator 1 compares the phases with each other between a 1st input signal 7 inputted from an input terminal T1 and a 2nd input signal 8 inputted from a frequency divider 5 and outputs the difference of both phases. This phase difference is converted into a DC signal by a charge pump 2, and the DC signal includes the high and low frequency components, the noises, etc. The high frequency component and noises are eliminated by an LPF 3, and only the low frequency component is outputted as the control voltage of a voltage controlled oscillator 4. In this instance, the ON resistance of a transistor that constructs the pump 2 is served also as the resistance of the LPF 3. As a result, the capacitor value of the LPF 3 is reduced since the resistance can be increased for the cut-off frequency that is needed for the LPF 3. |
