| 摘要 |
Improvement of the signal-to-noise ratio for a wideband video signal is effected by subtraction from the wideband video signal of a signal which follows low-amplitude excursions of the video signal's high frequency component. The latter signal is formed by a circuit arrangement which includes a high pass filter, of a C-R differentiator form, coupled to the input of an amplifier. A negative feedback path, coupled between the amplifier output and the junction of capacitive and resistive elements of the differentiator includes threshold devices which permit activation of the negative feedback path only during input signal excursions which exceed selected close-to-axis limits. The threshold device disposition relative to the high pass filter elements is such that negative feedback path activation also serves to introduce an appreciable reduction in the effective time constant of the differentiator, whereby a rapid return from a large input signal excursion beyond one of the selected limits may be followed at the amplifier input. In an illustrative use, the noise reduction circuitry is advantageously employed to process a luminance signal component separated by comb filtering from a composite signal recovered during playback of a video disc, with the subtraction step being effected in apparatus also serving to recombine separated luminance and chrominance components for formation of the disc player's output composite signal.
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