| 摘要 |
PURPOSE:To prevent the filter characteristic from deterioration when a weak electric field is inputted and to obtain a high quality picture reproduction for a wide range of inputted electric field strength, by enlarging the time constant of the loop filter by the AGC voltage when the weak electric field is inputted. CONSTITUTION:A horizontal and a vertical synchronizing signal from a synchronizing separator circuit 20 and a fly-back pulse from a horizontal transformer 30 are received by a phase detecting circuit 21 in an integrated circuit IC, and the detected output form the circuit 21 is outputted to a terminal 14. The oscillating frequency is controlled by adding the output from the terminal 14 to a loop filter composed of a condenser C4, resistances R7-R9, etc., and the detected output which is transformed into DC to a horizontal oscillating circuit 22 consisting a voltage control oscillating circuit from a terminal 12. The time constant of the loop filter is switched in accordance with the AGC voltage which is to be applied to the base of a transistor TRQ1 connected to the space between resistances R8 and R9 and the base of another TRQ2 connected to the base of the TRQ1. Thus the filter characteristic is prevented from deterioration and high quality pictures are reproduced, by enlarging the time constant of the filter when a weak electric field is inputted. |
