| 摘要 |
PURPOSE:To obtain correct synchronization and further, to shorten a synchronous catching time by closing a normal DLL loop (delay lock loop) when the correlative output of a leading phase arrives at a reference level near a peak value. CONSTITUTION:At the beginning of a synchronous search, an output 12a of an RS latch 12 goes to be '1' and the switch of a switch circuit 10 is caused to be in a VS side. Then, the DLL loop is opened and VCO (voltage control oscillator) 106 is driven by a constant direct current voltage VS. A phase difference detecting signal 203 is closed to a synchronous condition and when the correlative output level of the leading phase rises up and goes over a reference voltage Vrf, the output of a comparator 11 goes to be '1'. Then, the output 12a of the RS latch 12 goes to be '0' and the switch CIRCUIT 10 changes over the switch to a phase difference detecting signal 203 side. After that, the loop is closed and synchronous catching and tracing is executed by operation same as a conventional DLL circuit. Thus, phase transition can be speedily executed and synchronization can be executed to a correct stable point. Then, danger to be a pseudo-stable point is erased. |
