Circuit for switching video sources

Claim 2

A circuit for rapidly switching, in a television receiver, between at least three separate video sources which are connectable to a video processing stage providing the display of a picture, said circuit comprising at least a first change-over switch in cascade with a second change-over switch, the first change-over switch having an output coupled directly to the video processing stage, a first input coupled to one of said at least three separate video sources, and a second input; and the second change-over switch having an output coupled to the second input of said first change-over switch and inputs coupled, respectively to the others of said at least three separate video sources the switching action of said circuit being controlled by a plurality of control signals emitted by a control signal means coupled to said second change-over switch, characterized in that said first change-over switch has a switching speed substantially faster than that of said second change-over switch and that the control signal means includes a timing circuit which preserves said control signals during at least one field period, wherein the switching speed of said first change-over switch establishes the switching speed of said rapidly switching circuit.

Claim 3

A circuit as claimed in claim 1, wherein the timing circuit comprises a logic circuit which preserves a said control signals during at least one field period.

Claim 4

A circuit as claimed in claim 3, wherein the logic circuit operates in response to field pulses and said control signals such that when said control signals have a short duration and occurs at least once in every field period said control signals are maintained by said logic circuit up to the end of a subsequent field period

Claim 5

A circuit as claimed in claim 3, wherein the logic circuit comprises a divide-by-two divider for dividing a field frequency which produces a field signal alternately on a first output and on a second output and in that these two outputs are each coupled to an input of a respective bistable trigger circuit R-S whose other input receives said control signals, the outputs of these bistable trigger circuits R-S being each coupled to a respective input of a logic gate whose output applies said preserved control signals to the second change-over switch.

Claim 6

A circuit as claimed in claim 3, wherein the logic circuit comprises a field pulse counter, having a maximum count of at least two, which is reset to zero by said control signals and a bistable trigger circuit R-S having one input coupled to an output of said field pulse counter and a second input energized by said control signals.

Claim 7

A circuit for rapidly switching, between a main source and one of a plurality of auxiliary sources of video which are connectable to a video processing stage providing the display of a television picture, said circuit comprising: a first change-over switch having first and second inputs, said first input coupled to said main source, and an output coupled to said video processing stage, said first change-over switch having a first switching rate for alternately switching said first and second inputs to said output; a second change-over switch having an output coupled to said second input of said first change-over switch and a plurality of inputs each coupled to ones of said plurality of auxiliary sources for selectable connecting one of said auxiliary sources to said first change-over switch, said second change-over switch having a second switching rate for alternately switching said plurality of inputs to said output; and a control signal means coupled to said second change-over switch for providing a plurality of control signals to said second change-over switch, said control signal means comprising a means for storing said control signals during at least one field period, wherein said first switching rate is substantially faster than said second switching rate and said first switching rate establishes the switching speed of said rapidly switching circuit..

Claim 8

A circuit for rapidly switching, between a main source and one of a plurality of auxiliary sources of video which are connectable to a video processing stage providing the display of a television picture, said circuit comprising: a first change-over switch having first and second inputs, said first input coupled to said main source, and an output coupled to said video processing stage, said first change-over switch having a first switching rate for alternately switching said first and second inputs to said output; a second change-over switch having an output coupled to said second input of said first change-over switch and a plurality of inputs each coupled to ones of said plurality of auxiliary sources for selectable connecting one of said auxiliary sources to said first change-over switch, said second change-over switch having a second switching rate for alternately switching said plurality of inputs to said output; and a control signal means coupled to said second change-over switch for providing a plurality of control signals to said second change-over switch, said control signal means comprising a means for storing said control signals during at least one field period, wherein said first switching rate is substantially faster than said second switching rate and said first switching rate establishes the switching speed of said rapidly switching circuit..

Claim 9

A circuit as claimed in claim 6, wherein a connection to the video processing stage is effected via three-wire links "red, green, blue" and that said first and second change-over switches are three-fold switches.

Claim 10

A circuit as claimed in claim 7, wherein said control signal means comprises an avalanche semiconductor assembly which is rendered conductive by the control signal and is cut-off by a field signal, arranged in series with a time-constant circuit having a resistance-capacitance time constant which is equal to or longer than said one field period.

Claim 11

A circuit as claimed in claim 6, wherein said control signal means comprises an analog circuit having resistance-capacitance time constants.