| 摘要 |
PURPOSE:To obtain a picture with good quality suitable for a tape recorder in response to both a strong and a weak TV electromagnetic wave, by detecting the phase shift between a horizontal synchronizing signal and a horizontal deflecting output, smoothing its output and switching the result with a filter output. CONSTITUTION:The horizontal synchronizing signal from a horizontal synchronizing signal input terminal 8 is inputted to a phase detecting circuit 1 of the horizontal deflecting circuit driving a horizontal deflecting coil of a CRT to detect the phase shift between the horizontal synchronizing signal and the horizontal deflecting output from a horizontal drive output circuit 3. This detected output is smoothed at an LPF7, inputted to a horizontal oscillating circuit 2, a horizontal deflecting output is generated and applied to an output circuit 3. The time constant determined with a resistor 5 and capacitors 4, 6 of the LPF7 is switched via an NPN TR12 controlled with an automatic gain control voltage (IF-AGC voltage) 13 of a video IF amplifier circuit. Further, the time constant is switched depending whether the voltage 13 is larger than a predetermined value or smaller, allowing to improve the quality of picture corresponding to both the weak and strong TV electromagnetic waves. |
