| 摘要 |
PURPOSE:To switch a generating frequency stably at a high speed. CONSTITUTION:Photocouplers 9, 10 are used for the switching of a current gain of a charge pump circuit 4 in a PLL circuit switching the generating frequency, and photocouplers 11, 12, 13, 14 are used for switching a time constant of a loop filter circuit 5. When a capacitor 20 is charged at frequency switching, photocouplers 5, 7, 9 are conductive, and when the capacitor 20 is discharged, photocouplers 6, 8, 10 are conductive to decrease the time constant and charge/ discharge of the capacitor 20 is quickly implemented thereby switching the frequency at a high speed. |
