| 摘要 |
PURPOSE:To attain the frequency modulation by a modulation signal including a DC component by providing a switch circuit to an integration device at the input side of a phase locked loop circuit and activating the switch circuit at a period in response to a voltage so as in discharge the electric charge in the integration device. CONSTITUTION:An integration device 5 is provided into a path from an input terminal P1 for a modulation signal to a loop filter 3 in a phase locked loop circuit for a feedback system, in which a comparison frequency fR from a reference oscillator 1 is introduced to a closed loop having a phase comparator 2, the loop filter 3 and a voltage controlled oscillator 4 and an oscillating frequency fVCO of the voltage controlled oscillator 4 is controlled depending on the comparison between a frequency fV fed back from the voltage controlled oscillator 4 and the comparison frequency fR at a phase comparator 2. The integration device 5 discharges the stored charge by a switch circuit SW1. The switch circuit SW1 is operated by using a pulse signal from a discharge pulse generator 6 as a trigger. A pulse signal is generated from the discharge pulse generator 8 when an output of the phase comparator 2 exceeds a prescribed threshold level. |
