| 摘要 |
A method of and an apparatus for securely and precisely extracting from a received television signal a start pulse signal which is a binary signal provided at the beginning of an information signal multiplexed in the vertical blanking period of the television signal is disclosed. A PLL circuit acting as a frequency multiplier is provided to obtain a multiplied-frequency signal synchronized with a horizontal synchronizing signal (separated from the television signal by a synchronizing separator circuit) and having a frequency N times equal to or higher than a horizontal synchronizing frequency, first and second extracting gate pulses are formed from the multiplied-frequency signal, the start pulse signal is extracted from the received television signal by the first extracting gate pulse, the extracted start pulse signal is made to pass through a filter resonating with the start pulse signal to remove a noise component, a waveform at a central portion of the filtered start pulse signal is extracted by the second extracting gate pulse, and the extracted waveform is produced as a start pulse for bit synchronization of the information signal. |
