Video signal switching step suppressor

Claim 2

In a video signal switcher having an input which is switched from a first to a second source of video signal, the average picture levels of which may differ, apparatus for suppressing abrupt changes in the blanking level to the resultant video signal produced in the output of the switcher, said apparatus comprising: utilization means for the resultant video signal; a coupling capacitor having an input terminal coupled to said switcher output and an output terminal coupled to said utilization means; storage means for storing a reference potential representative of the blanking level of said first video signal coupled to the output terminal of said coupling capacitor; clamping means connected between said capacitor output terminal and said storage means; means for activating said clamping means while both of said first and second video signals are at their respective blanking levels to hold said capacitor output terminal at said reference potential; and means operable for switching the input of said switcher from said first to said second source of video signal during said activation period of said clamping means to effect charging of said coupling capacitor to the difference between the blanking level potential of said second video signal and said reference potential.

Claim 3

Apparatus as defined in claim 1, and additionally including: blanking level measuring means coupled between the output terminal of said coupling capacitor and said storage means.

Claim 4

Apparatus as defined in claim 2, and additionally including: a normally closed disconnect switch coupled between said blanking level measuring means and said storage means; and means for opening said disconnect switch during said activation period of saId clamping means.

Claim 5

In a video signal switcher having an input which is switcher from a first to a second source of video signal, the average picture levels of which may differ, apparatus for suppressing abrupt changes in the blanking level of the resultant video signal produced in the output of the switcher, said apparatus comprising: utilization means for the resultant video signal; a coupling capacitor having an input terminal coupled to said switcher output and an output terminal coupled to said utilization means; clamping means connected between said capacitor output terminal and a source of reference potential; means for activating said clamping means while both of said first and second video signals are at their respective blanking levels to hold said capacitor output terminal at said reference potential; means operable for switching the input of said switcher from said first to said second source of video signal during said activation period of said clamping means to effect charging of said coupling capacitor to the difference between the blanking level potential of said second video signal and said reference potential; the time constant of the switcher output circuit including said coupling capacitor in combination with said video signal switcher output and said clamping means is sufficiently small that the blanking level of said second video signal is substantially at said reference potential when said input switching means is operated, said switcher output circuit thereby constituting a high pass filter which discriminates against low-frequency video signals; and low-frequency boosting means coupled between said switcher output circuit and said utilization means.

Claim 6

In a video signal switcher having an input which is switcher from a first to a second source of video signal, the average picture levels of which may differ, apparatus for suppressing abrupt changes in the blanking level of the resultant video signal produced in the output of the switcher, said apparatus comprising: utilization means for the resultant video signal; a coupling capacitor having an input terminal coupled to said switcher output and an output terminal coupled to said utilization means; clamping means connected between said capacitor output terminal and a source of reference potential; means for activating said clamping means while both of said first and second video signals are at their respective blanking levels to hold said capacitor output terminal at said reference potential; means operable for switching the input of said switcher from said first to said second source of video signal during said activation period of said clamping means to effect charging of said coupling capacitor to the difference between the blanking level potential of said second video signal and said reference potential; the time constant of the switcher output circuit including said coupling capacitor in combination with said video signal switcher output and said clamping means is sufficiently small that the blanking level of said second video signal is substantially at said reference potential when said input switching means is operated, said switcher output circuit thereby constituting a high pass filter which discriminates against low-frequency video signals; and low-frequency boosting means coupled between said switcher output circuit and said utilization means.

Claim 7

Apparatus as defined in claim 4, and additionally including: negative feedback means coupled between the output of said low-frequency boosting means and said video signal input to counteract the effect of any difference in time constants of said constituted high pass filter and said low-frequency boosting means, thereby effectively providing the apparatus with a substantially uniform response to all video signal frequencies.