Circuit for selectively limiting voltage magnitudes

Claim 2

A clipping circuit adapted to be connected between a signal path and a first terminal providing a first reference potential for limiting the magnitudes of a signal, having a first polarity and occurring on the signal path, to a level which is a function of the normal magnitude of the signal, such clipping circuit including in combination: electron control means having an input terminal adapted to be connected to the signal path and an output terminal, said electron control means allowing current flow in one direction in response to the signal; capacitor means connected between said output terminal of said electron control means and the first terminal, said capacitor means providing at said output terminal a second reference potential which depends solely upon the normal magnitude of the signal in response to said current flow through said electron control means; voltage controlled switch means having first and second electrodes, said switch means normally providing a high impedance between said first and second electrodes, said switch means providing a predetermined voltage between said first and second electrodes in response to a voltage applied between said first and second electrodes having a magnitude exceeding such predetermined voltage; first circuit means coupling said first electrode of said switch means to said input terminal of said electron control means; and second circuit means coupling said second electrode of said switch means to said output terminal of said electron control means; said voltage controlled switch means being rendered conductive in response to a signal having an instantaneous magnitude greater than said predetermined voltage above said second reference potential to limit the magnitude of the signal in the signal path to substantially said predetermined voltage above said second reference potential.

Claim 3

The clipping circuit of claim 1 wherein said capacitor means includes first and second plates, said first plate being connected to said output terminal of said electron control means, said second plate being connected to the first terminal providing the first reference potential.

Claim 4

The clipping circuit of claim 2 wherein said electron control means further includes a first resistor means connected in series with diode means between said input terminal and said output terminal thereof, said resistor means having a selected value which allows said reference level across said capacitor means to vary with the variation of the normal peak magnitudes of the signal over a preselected time.

Claim 5

The clipping circuit of claim 2 further including second resistance means connected between said first and second plates of said capacitor means, said second resistance means selectively controlling the discharge rate of said capacitor means.

Claim 6

The clipping circuit of claim 1 wherein said voltage controlled switch means further includes a third electrode which is adapted to be connected to the first terminal providing the first reference potential.

Claim 7

The clipping circuit of claim 5 wherein said voltage controlled switch means includes: first transistor means having emitter, base and collector electrodes, said emitter electrode of said first transistor means being connected to said first electrode of said switch means, said collector electrode of said first transistor means being connected to said third electrode of said switch means; second transistor means having emitter, base and collector electrodes, said emitter electrode of said second transistor means being connecTed to said collector electrode of said first transistor means; and diode means having first and second terminals, said first terminal of said diode means being connected to said base electrode of said second transistor means, said second electrode of said diode means being connected to said second electrode of said voltage controlled switch means.

Claim 8

The clipping circuit of claim 1 wherein said first circuit means includes an inductance means.

Claim 9

A limiting circuit which is adapted to be connected between a video signal path and a terminal providing a first reference potential and which limits the magnitude of peak white video signals to a value which is a function of the normal white magnitudes of the video signal, such limiting circuit including in combination: electron control means having diode means connected between an input terminal adapted to be connected to the signal path and an output terminal, said diode means allowing current flow in one direction in response to each of the normal white magnitudes of the video signal; capacitor means having a first plate connected to said output terminal of said electron control means and a second plate adapted to be connected to the terminal providing the first reference potential, said capacitor means being responsive to said current flow through said diode means to provide a second reference potential which varies automatically with changes in said normal white magnitudes of the video signal; voltage controlled switch means having first, second and third electrodes, said switch means normally providing a high impedance between said first and second electrodes, said switch means providing a predetermined voltage between said first and second electrodes in response to a voltage applied between said first and second electrodes which has a magnitude exceed such predetermined voltage; inductor means coupling said first electrode of said switch means to said input terminal of said first electron control device; circuit means coupling said second electrode of said switch means to said first plate of said capacitor means; and means for coupling said third electrode of said switch means to the terminal providing the first reference potential; said voltage controlled switch means being rendered conductive in response to the instantaneous peak white magnitudes of the video signal which reach a voltage greater than said predetermined voltage plus said second reference potential to limit the magnitudes of said peak white signals to said predetermined voltage plus said second reference potential.

Claim 10

A limiting circuit which is adapted to be connected between a video signal path and a terminal providing a first reference potential and which limits the magnitude of peak white video signals to a value which is a function of the normal white magnitudes of the video signal, such limiting circuit including in combination: electron control means having diode means connected between an input terminal adapted to be connected to the signal path and an output terminal, said diode means allowing current flow in one direction in response to each of the normal white magnitudes of the video signal; capacitor means having a first plate connected to said output terminal of said electron control means and a second plate adapted to be connected to the terminal providing the first reference potential, said capacitor means being responsive to said current flow through said diode means to provide a second reference potential which varies automatically with changes in said normal white magnitudes of the video signal; voltage controlled switch means having first, second and third electrodes, said switch means normally providing a high impedance between said first and second electrodes, said switch means providing a predetermined voltage between said first and second electrodes in response to a voltage applied between said first and second electrodes which has a magnitude exceed such predetermined voltage; inductor means coupling said first electrode of said switch means to said input terminal of said first electron control device; circuit means coupling said second electrode of said switch means to said first plate of said capacitor means; and means for coupling said third electrode of said switch means to the terminal providing the first reference potential; said voltage controlled switch means being rendered conductive in response to the instantaneous peak white magnitudes of the video signal which reach a voltage greater than said predetermined voltage plus said second reference potential to limit the magnitudes of said peak white signals to said predetermined voltage plus said second reference potential.

Claim 11

The clipping circuit of claim 8 wherein said voltage controlled switch means includes; first transistor means having emitter, base and collector electrodes, said emitter electrode of said first transistor means being connected to said first electrode of said switch means, said collector electrode of said first transistor means being connected to said third electrode of said switch means; second transistor means having emitter, base and collector electrodes, said emitter electrode of said second transistor means being connected to said base electrode of said first transistor means, said collector electrode of said second transistor means being connected to said collector electrode of said first transistor means; and diode means having first and second terminals, said first terminal of said diode means being connected to said base electrode of second transistor means, said second electrode of said diode means being connected to said second electrode of said voltage controlled switch means.

Claim 12

The peak white clipping signal of claim 8 wherein said electron control means further includes first resistor means for limiting the charging time constant of said capacitor means so that said second reference level is virtually non-responsive to a peak white signal.

Claim 13

The peak white limiting circuit of claim 10 further including a second resistor means connected in parallel witH said capacitor means for controlling the discharge time constant thereof so that said second reference level varies with changes in the average magnitudes of said normal white video signal.