Video signal noise elimination circuit

Claim 2

A noise protection arrangement for a television receiver comprising: means for deriving, from a received television signal, a composite video signal having desired video and sync components varying within a predetermined amplitude range between and defined by sync tip and white levels, but subject to the introduction of undesired noise components each extending with decreasing width in the direction of said sync components and to a peak amplitude beyond both said sync tip level and a predetermined noise threshold level lying outside of said range; control means, including pulse-stretching means, for producing in response to each noise component a noise protection pulse of a duration at least greater than the width of the associated noise component as measured at said noise threshold level; and immunizing means, including video signal delay means and matrixing means, responsive to said noise protection pulses for minimizing deleterious effects of said noise components on the operation of said television receiver.

Claim 3

A noise protection arrangement according to claim 1 in which each of said noise protection pulses has a duration greater than the maximum width of its associated noise component.

Claim 4

A noise protection arrangement according to claim 2 in which said immunizing means utilizes each noise protection pulse to modify said composite video signal to delete therefrom the entirety of the associated noise component and develop a resultant composite video signal devoid of any noise contamination both above and below said noise threshold level.

Claim 5

A noise protection arrangement according to claim 1 and including a sync separator for separating said sync components from said composite video signal, and in which said immunizing means utilizes said noise protection pulses to effectively render said sync separator immune to said noise components.

Claim 6

A noise protection arrangement according to claim 1 and including an automatic gain control system for regulating the gain of said receiver inversely with signal strength variations of the received television signal, and in which said immunizing means utilizes said noise protection pulses to effectively render said automatic gain control system immune to said noise components.

Claim 7

A noise protection arrangement according to claim 2 in which said immunizing means includes noise removal means responsive to each noise protection pulse for removing from said composite video signal the entirety of the associated noise component, including the component''s relatively broad portion which lies within the amplitude region between and defined by said noise threshold level and said white level, said noise removal means establishing said composite video signal at a fixed desired amplitude level throughout the entire duration of each noise component.

Claim 8

A noise protection arrangement according to claim 2 in which said control means includes an amplitude-sensitive noise separator for producing, in response to the relatively narrow portion of each noise component which extends beyond said noise threshold level, a noise control pulse of a duration equal to the width of the associated noise component as measured at said noise threshold level, and in which each of said noise protection pulses is produced from a different respective one of said control pulses.

Claim 9

A noise protection arrangement according to claim 7 in which said control means includes a wave-shaping circuit for stretching each of said noise control pulses to form said noise protection pulses.

Claim 10

A noise protection arrangement according to claim 2 in which said immunizing means includes a delay network for delaying said composite video signal in order that each noise protection pulse overlaps the leading and trailing edges of its associated noise component in the delayed video signal.

Claim 11

A noise protection arrangement according to claim 9 in which said immunizing means includes a matrix circuit for effectively subtracting said noise protection pulses from the delayed video signal.

Claim 12

A noise protection arrangement according to claim 10 in which said matrix circuit includes an impedance to one terminal of which is supplied the delayed video signal with its noise components being of one polarity, and to the other terminal of which is supplied said noise protection pulses with opposite polarity, said resultant composite video signal being derived from said other terminal.

Claim 13

A noise protection arrangement according to claim 1 and including a sync separator for separating said sync components from said composite video signal, and in which said immunizing means employs said noise protection pulses as cancellation pulses to neutralize said noise components and render them ineffective with respect to the operation of said sync separator.

Claim 14

A noise protection arrangement according to claim 1 and including a sync separator, threshold-biased to respond to said composite video signal when its instantaneous amplitude reaches a predetermined sync clipping level, for separating said sync Components from said composite video signal; in which each of said noise protection pulses has a duration at least greater than the width of its associated noise component as measured at said sync clipping level; and in which said immunizing means utilizes the noise protection pulses to effectively render said sync separator immune to said noise components.

Claim 15

A noise protection arrangement according to claim 2 in which said video components occur during spaced-apart trace intervals of said composite video signal and said sync components occur during intervening retrace intervals, and including a keyed automatic gain control system for regulating the gain of said receiver in accordance with the peak amplitude of each of said sync components, and in which said immunizing means includes disabling means responsive to said noise protection pulses for disabling said automatic gain control system throughout the entire duration of each noise component, thereby to prevent false operation of said gain control system otherwise resulting in response to said noise components.

Claim 16

A noise protection arrangement according to claim 14 in which said automatic gain control system includes a voltage generator, having a normally cutoff AGC gate enabled during each retrace interval and threshold biased to sample each sync component whose peak amplitude reaches a predetermined AGC reference level, for developing from such samplings an automatic gain control voltage the magnitude of which represents the strength of said received television signal, and means responsive to said automatic gain control voltage for regulating the gain of said receiver inversely with received signal strength variations to maintain a substantially constant peak-to-peak amplitude of said video and sync components and to maintain a fixed relationship between the peak amplitude of said sync components and said AGC reference level, and wherein said disabling means includes a noise gate which, in response to each protection pulse, disables said AGC gate thereby to prevent sampling of any noise component whose instantaneous amplitude lies, during a retrace interval, between said AGC reference level and said noise threshold level.