| 摘要 |
PURPOSE:To lock a PLL quickly just after starting and to apply stable PLL lock afterward by controlling a time constant of a circuit integrating an output frequency of a reference oscillator and a variable reactance FM modulator through the phase comparison depending on the difference of the phases. CONSTITUTION:The phase of an output frequency of a reference oscillator 2 excited from a crystal oscillator 1 and an output frequency of the variable reactance FM modulator 4 are compared (3). The phase difference is subject to integration 5, the result is mixed with a voice signal input at a mixer 6, the result is modulated by a variable reactance FM modulator 4, the output is inputted to the phase comparator 3. The PLL is formed in this way. The PLL is locked up in a short time constant by the control of a time constant controller 10 in a short time during a short time when the PLL is unlocked just after starting and then a longer time constant is selected. Thus, the noise production time at the reception side due to missing of the voice signal is decreased and the stable modulation in the center frequency is atained with out being affected by the voice signal after lockup. |
