| 摘要 |
A synchronous signal separation circuit 2 for separating horizontal synchronous signal HSn is connected to a horizontal synchronous signal detection circuit 3, which includes a switch 4, an oscillator 5 and a window signal generator 6 for generating a window signal WP. The switch 4 passes the separated horizontal synchronous signal HSn during an open-period of the window signal WP and intercepts the separated horizontal synchronous signal HSn during a close-period of the window signal. The oscillator 5 generates a rate signal having a period equal to a horizontal scan period synchronously with a change in an output signal HS from the switch circuit, and adjusts a time duration of the open period of the window signal so as to make a timing of a change in the output signal HS coincide with a generation timing of the rate signal while the open-period of the window signal is synchronized with the generation timing of the rate signal. With this adjustment of the time duration of the open-period, the correct horizontal synchronous signal HS in the separated horizontal synchronous signal HSn can be detected highly precisely via the switch circuit.
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