| 摘要 |
PURPOSE:To make stable receiving possible, by holding the frequency control signal in the state before the time below during the time when detection of the synchronizing signal is broken because of a high input signal level. CONSTITUTION:When synchronizing signal detecting circuit 12 detects the synchronizing signal included in the input signal, the sweep counter generating the automatic tuning voltage is controlled to perform tuning automatically. Meanwhile, if the input signal is excessive, the synchronizing signal is not detected, and the synchronizing signal lack period is generated. During this period, since transistors TRQ1 and Q2 are turned off, diode D5 is turned on, and a current is flowed through the emitter and the base of TRQ4, resistance R0, and diode D5, and the potential of output terminal P4 is lowered though TRQ4 is turned off, and thus, the sweep counter is not operated to hold stable receiving. |
