| 摘要 |
PURPOSE:To prevent a step-out from being caused even if a voltage-controlled oscillator has variance in center frequency by adding a control loop capable of expanding a frequency pull-in range. CONSTITUTION:The auxiliary control loop 200 for expanding the frequency pull-in range in further connected to an automatic frequency control loop 100. The auxiliary control loop 200 generates the 1st and the 2nd pulse trains C and E by utilizing the signal of a counter 25 in an equivalent pulse removing circuit 12. An inverter 27 and a latch circuit 28 are provided, and latch circuits 29 and 20 which latch the 1st and the 2nd pulse trains C and E with a reset pulse B from a differentiating circuit 24 are provided. A discriminating circuit 31 makes a logical decision on whether or not the frequency of oscillation pulses of the voltage-controlled oscillator is in the pull-in range of the control loop 100 on the basis of the contents of the outputs of the latch circuits 29 and 30 and a control signal to the voltage-controlled oscillator 13 is corrected through an adder 26 according to the decision result. |
