| 摘要 |
PURPOSE:To attain the secure and stable synchronization decision without using an analog circuit by specifying the action of a counting means to execute the frequency-dividing action at the same period as the synchronizing signal based on a phase difference signal from a phase comparator and deciding with the counted value of the counting means. CONSTITUTION:For a phase comparator 32, when a phase error occurs at the signal of input terminals R and V, either of output terminals U1 and D1 goes to an 'L' level and when the phase error eliminated, both go to an 'H' level. A signal UD1, in which signals U1 and D1 and obtained through an AND gate 33, is made into the enable signal of a horizontal counter 34. In a phase locked condition, the signal UD1 becomes the 'H' level, the counter 34 becomes the enable and always, the stepping of the counting is executed. When the counted value exceeds the threshold at a 1H period and the time constant of a mono- stable mono-multi vibrator 38 is set to 1H or above, the output continues to always go to the 'H' and is decided to be the phase locked condition. The threshold of comparators 35 and 36 is made into S1, S2 (S1>S2), and at the time of no phase locking, a comparator 35 is selected and at the time of phase locking, 36 is selected. |
