Rca Inc.

Frank C Liu

Walter G Gibson

Max Ward Muterspaugh

Yih-Sien Kao

Impulse noise detection circuitry for determining the occurrence of short noise pulses in TV video signal includes two 1H delay lines to align successive image lines for signal comparison. The amplitude of signal from one image line is compared with the signal amplitude of a succeeding and a preceding image line along a vertical line. If the amplitude of the one signal concurrently exceeds the signal of both the preceding and the succeeding image lines, then a control signal, indicative of the presence of impulse noise, is produced.

Impulse noise detection circuit for TV signals

A video signal processing circuit including signal substitution circuitry for eliminating impulse noise has a signal peaking circuit conditionally operable for the duration of one or more video fields depending upon the presence of noise being detected in the vertical blanking interval. A circuit responsive to enabling pulses generated as a result of impulse noise or defects being detected in a vertical blanking interval provides one of two peaking control signals for controlling the level of peaking applied to the video signal by the peaking circuit.

Variable peaking control circuit

A video defect compensator is provided which develops a replacement or substitution video signal for use during a defect in the signal normally being displayed. The substitution signal is generated by averaging four picture points in the vicinity of the displayed picture point, two from the television line preceding the line currently being displayed and two from the television line succeeding the line currently being displayed. The four picture points are made available by utilizing a 2H delay line and wherein the line currently displayed is delayed by one TV line. Two signals temporally displayed by one color subcarrier period and delayed from the current signal by 1H are summed. Two signals temporally displaced by one color subcarrier period and preceding the currently displayed signal by 1H are also summed. The two sets of summed signals are then combined and divided by four to produce a replacement signal which is the average of four picture points.

Video signal defect replacement circuitry

An automatic fine tuning (AFT) circuit is provided which generates an AFT control signal in response to a video intermedate frequency (I.F.) signal. The I.F. signal is supplied to the input of a current source amplifier, which provides current signals of like phase relationship to a discriminator network. The discriminator network is comprised of two tuned circuits, one of which is resonant at a frequency below the desired frequency of the I.F. picture carrier, and the other resonant at a frequency above the desired frequency. The tuned circuits develop voltage variations which vary differentially in magnitude in response to the frequency deviation of the I.F. picture carrier from its desired frequency. The differentially related voltages are detected by two peak detector networks for use as AFT control signals. The current source amplifier and peak detector networks may be conveniently fabricated on a single I.C. chip. The tuned circuits are coupled to the current source amplifier and peak detector networks through two external I.C. terminals.

AFT Circuit

A selectivity network is provided for a synchronous detector, a reference signal circuit, and an AFT circuit. The selectivity network comprises a first tuned circuit coupled across two terminals of the reference signal circuit and tuned to the desired frequency of the I.F. picture carrier. A second tuned circuit is lightly coupled to the first tuned circuit and is coupled across two inputs of the AFT circuit to provide a frequency dependent phase-sifted reference signal to the AFT circuit. The first tuned circuit includes a trap circuit tuned to provide attenuation about a frequency intermediate the frequency of a sound carrier and that picture signal sideband frequency which, upon detection, results in a video signal corresponding to the intercarrier sound second subharmonic frequency. The trap in the reference signal tuned circuit minimizes quadrature distortion in the reference channel and the resultant harmonic distortion in the video signals, which causes sound buzz. The frequency notched reference signal is applied to the AFT tuned circuit, which causes a balancing of the pull-in range of the AFT circuit about the desired picture carrier frequency, thereby immunizing the AFT circuit against noise-pulling. The frequency notch in the AFT circuit at the indicated frequency also minimizes AFT effects of a frequency offset co-channel sound carrier, allowing the automatic acquisition of signals which are offset in frequency toward the lower adjacent channel.

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Phoenix, AZ, United States of America

Frank C Liu