| 摘要 |
PURPOSE:To reduce noises in a color signal by providing a filter, which decreases in band width when the level of the amplitude-modulated color signal is low, in a transmission line for the color signal. CONSTITUTION:A reproduced color signal from a magnetic tape is passed through a low-pass filter to extract a low-frequency converted color signal. This signal is supplied to the input terminal 14 of a band-width control circuit through an automatic chroma saturation regulating circuit. The band-width control circuit consists of a coil 18, a capacitor 9, a resistance 20, and two diodes 16 and 17, and the value of the resistance 20 is so set that the resonance frequency of the series resonance circuit consisting of the coil 18, capacitor 9, and resistance 20 is equal to a low-band carrier frequency. Consequently, when the color signal has great amplitude, the diodes 16 and 17 are nearly short- circuited and the band width is not limited, but when the amplitide is small, the impedance of the diode 16 and 17 increases to limit the color signal by the band width determined by the series resonance circuit, thereby obtaining an improve S/N ratio. |
