| 摘要 |
PURPOSE:To realize the reference signal generating circuit having a switching function in which the changeover to a standby system is attained immediately against to an interruption of a reference signal and an output frequency change of a PLL is suppressed small. CONSTITUTION:The circuit consists of 1st and 2nd reference signal generating means 10, 12 generating a signal of a reference frequency, 1st and 2nd frequency divider means 14, 16 frequency-dividing an output of the 1st and 2nd reference signal generating means 10, 12 at a prescribed frequency division ratio respectively, a delay means 18 delaying an output of the 1st frequency divider means 14 at a prescribed delay time, an OR means 20 ORing an input and an output of the delay means 18 whose output connects to a reset input to reset the operation of the 2nd frequency divider means 16, an exclusive OR means 22 exclusively ORing the output of the delay means 18 and the output of the 2nd frequency divider means 16, and a phase locked loop means 24 outputting a signal controlled in phase lock with an output signal of the exclusive OR means 22. |
