Noise-cancelling circuits

Claim 2

In a television receiver having a source of composite television signals including image brightness representative signal components and regularly recurring synchronizing signal components extending in amplitude beyond said image brightness representative signal components, the combination comprising, a. automatic gain control means including a transistor of a given conductivity arranged in a common emitter configuration and having an output collector electrode coupled to said source of composite signals for maintaining said synchronizing signals levels at a substantially fixed level, b. noise threshold means including a transistor amplifier of an opposite conductivity with respect to said given conductivity, and having a collector electrode, and an emitter electrode direct coupled to said composite television signal source, said transistor responsive to noise components exceeding said fixed level by a predetermined amount, c. a first voltage source, d. means coupled to said first voltage source for supplying a first fixed reference potential to said source of composite television signals and for supplying a second fixed reference voltage to said automatic gain control transistor and to said noise threshold transistor for establishing said fixed level, e. a synchronizing amplifier including a transistor of an opposite conductivity to said given conductivity having a base electrode coupled to said first voltage source for supplying a third reference level thereto, and an emitter electrode direct coupled to said composite television signal source, and f. means direct coupling said collector electrode of said noise threshold amplifier to said base electrode of said synchronizing transistor amplifier to cancel noise pulses which exceed said predetermined magnitude, according to said differences in said reference voltage levels.

Claim 3

The combination according to claim 1, wherein said noise threshold transistor and said synchronizing amplifier Transistors are arranged in common base configuration.

Claim 4

In a television receiver having a source of composite television signals including image brightness signal components and regularly recurring synchronizing signal components extending in amplitude beyond said image brightness signal components, said receiver including an amplifier having an input terminal coupled to said source of composite signals and an output terminal, the combination therewith, a. automatic gain control means including a transistor of a given conductivity arranged in a common emitter configuration, and having an emitter electrode, and a base electrode thereof directly coupled to said output terminal of said amplifier and having a collector output electrode coupled to said source of composite television signals for maintaining said synchronizing signal levels at a substantially fixed level, b. a noise canceller circuit including a transistor amplifier of an opposite conductivity with respect to said given conductivity, arranged in a common base configuration and having an emitter electrode direct coupled to said output terminal of said amplifier, and a base and collector electrode, c. a first voltage source, d. means coupled to said first voltage source for supplying to said base electrode of said noise canceller circuit transistor and said emitter electrode of said automatic gain control transistor a first reference potential and for supplying a second reference potential to said source of composite signals, the difference between said first and second potentials determinative of the peak amplitude of said composite signals, e. a synchronizing amplifier including a transistor of opposite conductivity to said given conductivity having a base electrode coupled to said first voltage source for supplying an operating potential thereto and an emitter electrode coupled to said output terminal of said amplifier, and f. means direct coupling said collector electrode of said noise canceller transistor to the base electrode of said synchronizing amplifier transistor to cancel noise pulses which exceed said predetermined magnitude, according to said difference in reference potentials, said conduction of said noise canceller transistor serving to load said amplifier at said output terminal to reduce the magnitude of noise pulses as applied to said base electrode of said automatic gain control transistor.

Claim 5

In a television receiver having a source of composite television signals including image brightness signal components and regularly recurring synchronizing signal components extending in amplitude beyond said image brightness signal components, said receiver including an amplifier having an input terminal coupled to said source of composite signals and an output terminal, the combination therewith, a. automatic gain control means including a transistor of a given conductivity arranged in a common emitter configuration, and having an emitter electrode, and a base electrode thereof directly coupled to said output terminal of said amplifier and having a collector output electrode coupled to said source of composite television signals for maintaining said synchronizing signal levels at a substantially fixed level, b. a noise canceller circuit including a transistor amplifier of an opposite conductivity with respect to said given conductivity, arranged in a common base configuration and having an emitter electrode direct coupled to said output terminal of said amplifier, and a base and collector electrode, c. a first voltage source, d. means coupled to said first voltage source for supplying to said base electrode of said noise canceller circuit transistor and said emitter electrode of said automatic gain control transistor a first reference potential and for supplying a second reference potential to said source of composite signals, the difference between said first and second potentials determinative of the peak amplitude of said composite signals, e. a synchronizing amplifier including a transistor of opposite conductivity to said given conductivity having a base electrode coupled to said first voltage source for supplying an operating potential thereto and an emitter electrode coupled to said output terminal of said amplifier, and f. means direct coupling said collector electrode of said noise canceller transistor to the base electrode of said synchronizing amplifier transistor to cancel noise pulses which exceed said predetermined magnitude, according to said difference in reference potentials, said conduction of said noise canceller transistor serving to load said amplifier at said output terminal to reduce the magnitude of noise pulses as applied to said base electrode of said automatic gain control transistor.

Claim 6

In a television receiver having a source of composite signals including image brightness representative signal components and regularly recurring synchronizing signal components extending in amplitude beyond said image brightness components, said receiver including a luminance amplifier having an input terminal direct coupled to said source and an output terminal direct coupled to an input terminal of an automatic gain control circuit for maintaining said synchronizing signal components at a substantially fixed level, in combination therewith, apparatus for cancelling noise pulses which exceed said fixed level comprising, a. a first transistor having a base, collector and emitter electrode direct coupled to said output terminal of said luminance amplifier, b. means coupled to the collector electrode of said first transistor and responsive to said synchronizing components to provide at an output an amplifier version thereof, c. a second transistor having a base, emitter and collector electrode, having the emitter electrode direct coupled to said output terminal of said luminance amplifier and said collector electrode direct coupled to said base electrode of said first transistor, d. a voltage source, e. means for coupling said base electrode of said first transistor to said voltage source, and f. means including a first resistor coupling said base electrode of said second transistor to said voltage source to bias said second transistor to cause said second transistor to conduct for signal levels above said fixed level, to provide at saId collector electrode signals in a direction to cut off said first transistor, said conduction of said second transistor further serving to load said luminance amplifier to decrease any signals during said conduction at said input terminal of said automatic gain control circuit.

Claim 7

In a television receiver having a source of composite signals including image brightness representative signal components and regularly recurring synchronizing signal components extending in amplitude beyond said image brightness components, said receiver including a luminance amplifier having an input terminal direct coupled to said source and an output terminal direct coupled to an input terminal of an automatic gain control circuit for maintaining said synchronizing signal components at a substantially fixed level, in combination therewith, apparatus for cancelling noise pulses which exceed said fixed level comprising, a. a first transistor having a base, collector and emitter electrode direct coupled to said output terminal of said luminance amplifier, b. means coupled to the collector electrode of said first transistor and responsive to said synchronizing components to provide at an output an amplifier version thereof, c. a second transistor having a base, emitter and collector electrode, having the emitter electrode direct coupled to said output terminal of said luminance amplifier and said collector electrode direct coupled to said base electrode of said first transistor, d. a voltage source, e. means for coupling said base electrode of said first transistor to said voltage source, and f. means including a first resistor coupling said base electrode of said second transistor to said voltage source to bias said second transistor to cause said second transistor to conduct for signal levels above said fixed level, to provide at saId collector electrode signals in a direction to cut off said first transistor, said conduction of said second transistor further serving to load said luminance amplifier to decrease any signals during said conduction at said input terminal of said automatic gain control circuit.

Claim 8

The apparatus according to claim 4 wherein said first and second transistors are the same conductivity types.

Claim 9

The apparatus according to claim 4 further comprising, a. means coupling said voltage source to said source of composite signals for supplying a first fixed reference potential thereto of a magnitude less than said fixed level.

Claim 10

The apparatus according to claim 4 further comprising, a. a capacitor coupled between said base electrode of said first transistor and a point of reference potential and selected to provide a relatively low reactance at the synchronizing signal component frequency.

Claim 11

In a color television receiver employing RF and IF amplifiers for responding to a transmitted television carrier signal and providing an IF signal output therefrom, said receiver including a video detector having an input coupled to an output of said IF amplifier for providing at an output of said video detector thereof a composite video signal, said receiver including a luminance channel and a chrominance channel for respectively driving a color kinescope included in said receivers for providing a color display, in combination therewith, apparatus for providing low level video signal processing, comprising, a. a first transistor of a given conductivity type arranged in an emitter follower configuration and having the base electrode thereof direct coupled to said output of said video detector, b. a source of operating potential having a relatively constant DC amplitude, c. means for coupling said source of operating potential to said base electrode of said first transistor to provide a DC operating potential thereto, d. second and third transistors of the same given conductivity types as said first transistor, each arranged in a common emitter configuration and having the base electrodes thereof direct coupled to the emitter electrode of said first transistor, e. means coupling the collector electrode of said second transistor to said chrominance channel, f. means coupling the collector electrode of said third transistor to said luminance channel, g. fourth and fifth transistors of the same conductivity types as said first transistor having the emitter electrodes coupled directly to the emitter electrode of said third transistor, h. a voltage divider coupling said base electrodes of said fourth and fifth transistors to said source of operating potential to bias said fifth transistor in a more forward direction in relation to saturation with respect to the bias of said fourth transistor, i. means coupling the collector electrode of said fourth transistor to the base electrode of said fifth transistor, j. a sixth transistor of an opposite conductivity with respect to that of said first transistor and having an emitter electrode coupled to said voltage divider between said base electrodes of said fourth and fifth transistors having a base electrode direct coupled to said emitter electrode of said third transistor, said collector electrode of said sixth transistor being coupled to said RF and IF amplifier for controlling the gain thereof and therefore controlling the amplitude of said composite video signal in accordance with the conduction of said sixth transistor, which as biased conducts when said composite video signal exceeds a predetermined DC level at said base electrode of said first transistor as biased from said source of operating potential, said fourth transistor as biased from said divider being responsive to signal levels at said emitter electrode which exceeds the signal necessary to cause conduction of said sixth transistor to cancel all such signals at said base electrode of said fifth tRansistor, said fourth transistor when conducting further serving to load said emitter electrode of said third transistor to reduce said excessive signal levels as applied to said base electrode of said sixth transistor.

Claim 12

In a color television receiver employing RF and IF amplifiers for responding to a transmitted television carrier signal and providing an IF signal output therefrom, said receiver including a video detector having an input coupled to an output of said IF amplifier for providing at an output of said video detector thereof a composite video signal, said receiver including a luminance channel and a chrominance channel for respectively driving a color kinescope included in said receivers for providing a color display, in combination therewith, apparatus for providing low level video signal processing, comprising, a. a first transistor of a given conductivity type arranged in an emitter follower configuration and having the base electrode thereof direct coupled to said output of said video detector, b. a source of operating potential having a relatively constant DC amplitude, c. means for coupling said source of operating potential to said base electrode of said first transistor to provide a DC operating potential thereto, d. second and third transistors of the same given conductivity types as said first transistor, each arranged in a common emitter configuration and having the base electrodes thereof direct coupled to the emitter electrode of said first transistor, e. means coupling the collector electrode of said second transistor to said chrominance channel, f. means coupling the collector electrode of said third transistor to said luminance channel, g. fourth and fifth transistors of the same conductivity types as said first transistor having the emitter electrodes coupled directly to the emitter electrode of said third transistor, h. a voltage divider coupling said base electrodes of said fourth and fifth transistors to said source of operating potential to bias said fifth transistor in a more forward direction in relation to saturation with respect to the bias of said fourth transistor, i. means coupling the collector electrode of said fourth transistor to the base electrode of said fifth transistor, j. a sixth transistor of an opposite conductivity with respect to that of said first transistor and having an emitter electrode coupled to said voltage divider between said base electrodes of said fourth and fifth transistors having a base electrode direct coupled to said emitter electrode of said third transistor, said collector electrode of said sixth transistor being coupled to said RF and IF amplifier for controlling the gain thereof and therefore controlling the amplitude of said composite video signal in accordance with the conduction of said sixth transistor, which as biased conducts when said composite video signal exceeds a predetermined DC level at said base electrode of said first transistor as biased from said source of operating potential, said fourth transistor as biased from said divider being responsive to signal levels at said emitter electrode which exceeds the signal necessary to cause conduction of said sixth transistor to cancel all such signals at said base electrode of said fifth tRansistor, said fourth transistor when conducting further serving to load said emitter electrode of said third transistor to reduce said excessive signal levels as applied to said base electrode of said sixth transistor.