| 摘要 |
PROBLEM TO BE SOLVED: To provide a video image switching detection circuit that suppresses the circuit scale from being increased and can attain the detection with high accuracy in spite of a smaller scale configuration. SOLUTION: The video image switching detection circuit is provided with a PLL circuit having a phase comparator 1, an LPF 2, a VCO 3, and a frequency divider 4. The phase comparator 1 compares an external HD that is an input signal resulting from shaping a horizontal synchronizing signal pulse with an internal HD that is a reference signal resulting from frequency-dividing an output pulse from the VCO 3 in the PLL circuit. The phase comparator 1 outputs an error signal when the phases of both the signals differ. A 1st counter 6 counts a period when the error signal is active, that is, a time when the phase difference takes place. Then a horizontal synchronizing signal discrimination section 9 discriminates a lock state of the horizontal synchronizing signal depending on the length of the phase difference consecutive time and an output circuit 15 outputs a video switching detection signal when the discrimination section 9 detects out of synchronism.
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