| 摘要 |
PURPOSE:To enhance responsiveness and also to stably keep locking. CONSTITUTION:When an MO signal is inputted in a PLL circuit 8, a time constant change-over switch 29 connects a time constant circuit 30 to an arithmetic amplifier 28. At this time, the time constant circuit 31 is not connected to the arithmetic amplifier 28 so that capacitors CY1 and CY2 excute self-discharge. Then, when an ID signal is inputted, the time constant change-over switch 29 connects the time constant circuit 31 to the arithmetic amplifier 28. Since the capacitors CY1 and CY2 have almost no electric charge, the capacitors CY1 and CY2 are charged. Thus, the time constant of a low pass filter 26 transitionally becomes smaller than the normal time constant of the time constant circuit 31 till charge is completed and becomes the normal time constant when charge is completed. In the same way, when the time constant circuit 30 is connected to the arithmetic amplifier 28 from the self discharge state of the capacitors CX1 and CX2, the time constant of the low pass filter 26 transitionally becomes small. |
