| 摘要 |
PURPOSE:To remove unstableness from phase-unlocked state detecting operation by generating pulse signals from an original signal and a feedback signal respectively, and detecting the crossing of those two pulse signals. CONSTITUTION:An input signal [original signal (a)] and the feedback signal (b) to the phase comparing circuit 1 of a phase-locked loop are inputted to a pulse generating circuit 6 respectively. The circuit 6 generates pulse signals (f) and (g) from the original signal (a) and feedback signal (b). The signals (f) and (g) are controlled in relative phase relation while the phase-locked loop is in a phase- locked state, so a pulse crossing detecting circuit 7 detects no crossing of the signals (f) and (g). When the phase-locked loop enters the phase-unlocked state, the relative phase relation between the signals (f) and (g) is not maintained any more and varies continuously in either direction, and the circuit 7 detects the crossing of the signals (f) and (g) synchronously to send a pulse crossing detection signal (h) to an unlocked-state detection output circuit 8, which outputs a phase-unlocked state detection output signal (e). |
