Special effects generators for providing iris-type television displays

Claim 2

In a special effects generator of the type for providing an iris display, said generator including an electronic switch for switching from a first video signal to a second video signal upon application of suitable control pulses thereto, provided by a control pulse generating circuit responsive to a composite parabolic waveform including the combination of a parabolic waveform at the vertical deflection rate and a parabolic waveform at the horizontal deflection rate, in combination therewith apparatus for providing increased sensitivity for said comparator when iris displays of small diameter are provided, comprising: a. a variable gain amplifier having an input terminal adapted to receive said composite parabolic waveform, an output terminal coupled to said control pulse generating circuit, and a gain control terminal, b. an integrator responsive to said control pulses to provide at an output thereof a DC control voltage proportional to the maximum width of said pulses, and c. means coupling said output terminal of said integrator to said gain control terminal of said variable gain amplifier.

Claim 3

The generator according to claim 1 wherein, said variable gain amplifier comprises a transistor, having an input base electrode, an output collector electrode, and an emitter control terminal.

Claim 4

The generator according to claim 2 further comprising, a. a second transistor arranged in an emitter follower configuration, having a base input electrode coupled to said integrator, and an emitter electrode coupled to said emitter electrode of said first transistor for shunting said electrode and thereby controlling the gain thereof in accordance with the magnitude of said DC control signal.

Claim 5

The apparatus according to claim 1 further comprising, a. a DC amplifier having an input terminal coupled to said integrator and responsive to said DC control signal to provide at an output terminal an amplified DC control signal, and b. means coupling said output terminal of said DC amplifier to said control terminal of said variable gain amplifier.

Claim 6

The apparatus according to claim 1 wherein said integrator includes a resistor and a capacitor.

Claim 7

A special effects generator for providing signals necessary to generate a circular type television display comprising in combination, a. an electronic switch having first and second inputs, each adapted to receive a different video signal, a control terminal for causing said signal at said first input to appear at an output terminal of said switch for a first voltage level applied thereto, and to cause said signal at said second input to appear at said output terminal for a second voltage level applied to said control terminal, b. a comparator circuit having a first input terminal adapted for application thereto of a composite parabolic waveform representative of said circular display, and a second terminal adapted to receive a reference level, said comparator operative to provide said first voltage level at an output terminal when the magnitude of said composite parabolic waveform exceeds said reference level, and to provide said second voltage level when the magnitude is lower than said reference level, said output terminal coupled to said control terminal of said switch, C. an integrator circuit having an input coupled to said output terminal of said comparator for providing a DC voltage according to the durations of the transitions of said comparator between said first and second levels, d. a variable gain amplifier having an input terminal adapted for application thereto of said composite parabolic waveform, and an output terminal coupled to said first input terminal of said comparator, said amplifier further having a gain control terminal coupled to said output terminal of said integrator to vary the gain of said amplifier according to the magnitude of said DC voltage.

Claim 8

A special effects generator for providing signals necessary to generate a circular type television display comprising in combination, a. an electronic switch having first and second inputs, each adapted to receive a different video signal, a control terminal for causing said signal at said first input to appear at an output terminal of said switch for a first voltage level applied thereto, and to cause said signal at said second input to appear at said output terminal for a second voltage level applied to said control terminal, b. a comparator circuit having a first input terminal adapted for application thereto of a composite parabolic waveform representative of said circular display, and a second terminal adapted to receive a reference level, said comparator operative to provide said first voltage level at an output terminal when the magnitude of said composite parabolic waveform exceeds said reference level, and to provide said second voltage level when the magnitude is lower than said reference level, said output terminal coupled to said control terminal of said switch, C. an integrator circuit having an input coupled to said output terminal of said comparator for providing a DC voltage according to the durations of the transitions of said comparator between said first and second levels, d. a variable gain amplifier having an input terminal adapted for application thereto of said composite parabolic waveform, and an output terminal coupled to said first input terminal of said comparator, said amplifier further having a gain control terminal coupled to said output terminal of said integrator to vary the gain of said amplifier according to the magnitude of said DC voltage.

Claim 9

The generator according to claim 6 wherein the gain of said variable gain amplifier increases as the DC voltage from said integrator decreases.