| 摘要 |
PURPOSE: To provide a lock detection circuit capable of being constituted of a digital circuit and accurately detecting lock without being affected by noise or the like. CONSTITUTION: This lock detection circuit 18 detects that a reference frequency and a feedback frequency are frequency-locked by using a reference counter 32 and a feedback counter 36. The reference counter and the feedback counter are respectively clocked by the reference frequency and the feedback frequency. In order to be frequency locked, two counted values are required to be equal both at the ends of first and second periods. A count window is generated from reference frequency signals and the range of the frequency of locking the feedback frequency is indicated. When the lock is achieved, the count window is widened and the feedback frequency is still present inside a lock range even in the case that aliasing is generated. |
