Cathode ray tube focussing system

Claim 2

In combination for reproducing a color image: first means for scanning the color image to produce signals representing a first and a second primary colors and a signal representing the luminance in the color image, the signals representing the first and second primary color having substantially the same frequency with differing phase, the first means including second means for focussing the first means on the color image during the scanning of the color image, wherein the first means provides a scanning beam and the second means includes a focus coil disposed relative to the scanning beam for producing a current to maintain the focus of the beam; third means responsive to the signals representing the first and second primary colors for producing a low frequency control signal having characteristics dependent upon the characteristics of the signals representing the first and second primary colors, wherein the third means is reponsive to the current in the focus coil to provide the control signal with characteristics dependent upon this current; and fourth means reponsive to the control signal for adjusting the focus provided by the first means in accordance with the characteristics of the control signal, the fourth means varying the current in the focus coil in accordance with the characteristics of the control signal, wherEin the fourth means comprises: first and second matched current controlling devices connected to each other at a first common terminal; third and fourth matched current controlling devices connected to each other at a second common terminal; the first and fourth current controlling devices connected to a reference signal and biased to conduct when the reference signal is positive; the second and third current controlling devices connected to a source of operating potential and biased to conduct when the reference signal is negative; fifth means having characteristics for dividing the conducted current between the first and second current controlling devices and the third and fourth current controlling devices in accordance with the phase of a particular voltage so that the magnitude of the correction current reflects the magnitude and direction of the focus coil current from the optimum value; wherein the current conducted through the first, second, third and fourth current controlling devices remains substantially constant and the current conducted by the first and third current controlling devices is the correction current.

Claim 3

A combination as recited in claim 1 wherein the fourth means further comprises: a source of negative operating potential; fifth and sixth matched current controlling devices connected to each other at the source of negative operating potential; the fifth current controlling device connected to the first common terminal and biased by the particular voltage; the sixth current controlling device connected to the second common terminal and biased by a referece potential such as ground; whereby the fifth current controlling device will conduct to a greater extent when the particular voltage is positive and the sixth current controlling device will conduct to a greater extent when the particular voltage is negative.

Claim 4

In combination for maintaining the electromagnetic focussing for a scanning beam in a color television camera tube: a focus coil disposed relative to the scanning beam for producing a current to produce a focus of the beam wherein the optimum focus corresponds to an optimum value for the focus coil current; means responsive to a first output signal from the color camera tube for producing a first control signal, the first output signal having characteristics dependent upon the characteristics of the focus current and a first primary color of an image; means responsive to a second output signal of the specified frequency from the color camera tube for producing a second control signal, the second output signal having characteristics dependent upon the characteristics of the focus current and a second primary color of the image, wherein a phase of the second output signal differs from a phase of the first output signal, wherein the means for providing the first and the second control signals includes: means for providing a reference signal; means for modulating the current in the focus coil with the reference signal to modulate the first and the second output signal, the modulated output signal having a phase dependent upon the direction of deviation of the current of the focus coil from the optimum value and having a magnitude dependent upon the magnitude of the deviation of the current in the focus coil from the optimum value, and means responsive to the first control signal and the second control signal for adjusting the current in the focus coil to maintain the focus current at the optimum value, the current adjusting means responding to the phase and amplitude of the modulated signal to adjust the current in the focussing coil to the optimum value, wherein the means for providing focus current adjustment comprises: a first conductor connected to the resistance means for transmitting the current adjustment thereto; a second conductor connected to the source of positive operating potential; a first pair of balanced current-controlling Devices such as a second and third current-controlling device is also connected to the first conductor and the third current-controlling device is also connected to the second conductor; a second pair of balanced current-controlling devices such as a fourth and fifth current-controlling device connected to each other wherein the fourth current-controlling device is also connected to the first conductor and the fifth current-controlling device is also connected to the second conductor; the second and fifth current-controlling devices commonly biased by the reference signal; the third and fourth current-controlling devices commonly biased by the source of positive operating potential; wherein the second and fifth current-contolling devices conduct when the reference signal is positive and the third and fourth current-controlling devices conduct when the reference signal is negative and the conducted current is correspondingly enabled in the first and second conductors; means connected to the common terminals of the first and second pairs and responsive to a particular voltage signal for dividing the current between a particular current-controlling devices which are conducted in accordance with the phase of the particular voltage; whereby a greater current will flow in the first current path if the particular voltage signal and the reference signal are in phase than if they are out of phase.

Claim 5

In combination for maintaining the electromagnetic focussing for a scanning beam in a color television camera tube: a focus coil disposed relative to the scanning beam for producing a current to produce a focus of the beam wherein the optimum focus corresponds to an optimum value for the focus coil current; means responsive to a first output signal from the color camera tube for producing a first control signal, the first output signal having characteristics dependent upon the characteristics of the focus current and a first primary color of an image; means responsive to a second output signal of the specified frequency from the color camera tube for producing a second control signal, the second output signal having characteristics dependent upon the characteristics of the focus current and a second primary color of the image, wherein a phase of the second output signal differs from a phase of the first output signal, wherein the means for providing the first and the second control signals includes: means for providing a reference signal; means for modulating the current in the focus coil with the reference signal to modulate the first and the second output signal, the modulated output signal having a phase dependent upon the direction of deviation of the current of the focus coil from the optimum value and having a magnitude dependent upon the magnitude of the deviation of the current in the focus coil from the optimum value, and means responsive to the first control signal and the second control signal for adjusting the current in the focus coil to maintain the focus current at the optimum value, the current adjusting means responding to the phase and amplitude of the modulated signal to adjust the current in the focussing coil to the optimum value, wherein the means for providing focus current adjustment comprises: a first conductor connected to the resistance means for transmitting the current adjustment thereto; a second conductor connected to the source of positive operating potential; a first pair of balanced current-controlling Devices such as a second and third current-controlling device is also connected to the first conductor and the third current-controlling device is also connected to the second conductor; a second pair of balanced current-controlling devices such as a fourth and fifth current-controlling device connected to each other wherein the fourth current-controlling device is also connected to the first conductor and the fifth current-controlling device is also connected to the second conductor; the second and fifth current-controlling devices commonly biased by the reference signal; the third and fourth current-controlling devices commonly biased by the source of positive operating potential; wherein the second and fifth current-contolling devices conduct when the reference signal is positive and the third and fourth current-controlling devices conduct when the reference signal is negative and the conducted current is correspondingly enabled in the first and second conductors; means connected to the common terminals of the first and second pairs and responsive to a particular voltage signal for dividing the current between a particular current-controlling devices which are conducted in accordance with the phase of the particular voltage; whereby a greater current will flow in the first current path if the particular voltage signal and the reference signal are in phase than if they are out of phase.

Claim 6

The combination as defined in claim 3 wherein the division means comprises: the third pair of balanced current-controlling devices such as a sixth and seventh current-controlling device is also connected to the common terminal of the second pair; the common terminal of the third current-controlling device pair is connected to the source of negative operating potential; the sixth current-controlling device is biased in part by the particular voltage signal and the seventh current-controlling device in part by the reference potential such as ground; and the sixth and seventh means having characteristics for conducting simultaneously in relative magnitudes corresponding to the instantaneous voltage of the particular voltage signal.