| 摘要 |
PURPOSE:To expand a frequency modulation characteristic to a low frequency and to enhance the response characteristic by decreasing the natural frequency of a PLL loop as time elapses in response to the pull-in operation of the PLL loop. CONSTITUTION:A PLL(Phase locked loop) circuit consists of a reference oscillator 1, a phase comparator 2, a loop filter 30, phase comparator output circuits 6l-6n, gate circuits 7l-7n and a selection control signal generating circuit 8. Then the natural frequency of the PLL loop is decreased as the time elapses from a prescribed value in response to the pull-in of the PLL loop. Thus, the frequency modulation characteristic is expanded up to a low frequency and the PLL circuit with the excellent response characteristic is obtained. |
