National Semiconductor Corporation

Charles Guan

Andrew John Morrish

Peyman Hojabri

Bias control circuitry and method for use in controlling one or more cathode ray tube (CRT) beam currents.

Bias control circuitry for cathode ray tube beam currents

Temperature compensation may be provided to a square function generator by adjusting a tail current of the square function generator. Temperature compensation of the square function generator may be provided, for example, by a second square function generator circuit and an error amplifier. The second square function generator may be substantially similar to the first square function generator. The error amplifier is arranged in cooperation with the first and second square function generators such that the output of the error amplifier adjusts the tail current of the square function generators. A plurality of temperature square function generators may be configured to provide a temperature-compensated cubic function. The temperature compensated cubic function may be used for S-correction in a display system such as a cathode ray tube.

Temperature compensated square function generator

A method and circuit for generating independent top and bottom corner correction using a single fourth order function is described. The top and bottom corner correction signal may be included in an east-west corrected voltage to correct an asymmetry of a picture with respect to a horizontal axis and a vertical axis of the picture. Two switch signals based on a ramping voltage, which is used to sweep an electron beam, and two clock signals control a sample-and-hold circuit. The sample-and-hold circuit is arranged to sample a fourth order voltage during a top portion and a bottom portion of the ramping voltage and provide two independent correction voltages Vand V. The correction voltages are then provided for top and bottom corner correction to the east-west corrected voltage.

Method of generating independent top and bottom corners correction using one 4th order function

Based, in part, on an input video signal, an autobias circuit generates red, green, and blue channel video signals, which are received by external drivers to drive cathodes in a CRT. The autobias circuit also provides gain and bias control signals based on a sense current. The external drivers generate the sense current such that the sense current is proportional to the sum of the beam currents flowing from the cathodes. The sense current has an error caused by current flowing through external recharge resistors. A correction current (Ivideo) is subtracted from the sense current to compensate. The correction current is generated according to the equation Ivideo=(Vs/Rkin)*[(Vref/Rext)/(Vref/Rin)], where Vkin and Rin are matched internal monolithic resistors, Rext is the resistance of another external resistor that is matched to the external recharge resistors, and Vs is the sum of the red, green, and blue channel video signals.

Circuit for generating a process-independent current

A digitally-controlled vertical S linearity correction with a constant amplitude without using an AGC. To preserve line spacing between horizontal lines toward a top and bottom of a screen a third order correction voltage Vis applied to a sweep voltage V. A constant current decoder determines an amount of appropriate correction current, which is employed to generate a sweep voltage with modified amplitude due to S correction and one without the modified amplitude. The sweep voltage with constant amplitude is employed to generate V. Vis then applied to the sweep voltage along with a compensated amplitude component of the sweep voltage, such that a reduction in the amplitude caused by the S correction is compensated in the output voltage V. The compensation of the output voltage amplitude prevents a size reduction of the displayed picture on the screen without employing an iterative auto-align process.

Digitally controlled vertical S linearity correction with constant amplitude without using an AGC

A method and circuit for digitally controlled vertical C linearity correction with constant start and end points without using an AGC. A squared voltage and a negative squared voltage are added as a correction voltage to a sawtooth-shaped ramping voltage that is employed to sweep an electron beam across a display. Line spacing toward the edges of a screen are maintained equal as a result enabling a uniform presentation of a picture on a non-spherical display. A digitally controlled attenuator determines a correction coefficient for correction voltages. The correction voltage is also processed by a sample-and-hold circuit to obtain a peak squared voltage. The peak squared voltage is then compared to a DC reference voltage and an offset adjustment current determined, based on a result of the comparison. The correction voltage is then added to the ramping voltage, which is also shifted by the offset amount.

Digitally controlled vertical C linearity correction with constant start and end points without using an AGC

A system for regulating beam current in a cathode ray tube. The system includes test signal timing and pulse generation logic for outputting test signals operable to stimulate a cathode ray tube at two voltage levels. The system further includes a circuit that inputs the test signal timing and determines correction signals based on signals derived from the cathode in response to stimulating the cathode ray tube at the two voltage levels. The correction signals may include a gain correction signal, a bias correction signal or both. The gain correction signal modifies a signal output to a gain driver that may be AC coupled to the cathode. The bias correction signal output to a clamping circuit coupled to the cathode.

System and method for regulating cathode ray tube beam current using autobias

A circuit for regulating a signal, such as a cathode current. The circuit has an input stage for inputting a signal and for producing a sense signal based thereon. The circuit may input timing signals and have a first stage for comparing a first reference signal with the sense signal when a first timing signal indicates and for outputting a first correction signal based on the comparison. The circuit may have a second stage for comparing a second reference signal with the sense signal when a second timing signal indicates and for outputting a second correction signal based on the comparison. The circuit may further have elements for measuring a leakage signal in the input signal during a third time interval. In this embodiment, the first and second stages are further for subtracting the leakage signal from the sense signal prior to the comparisons.

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San Francisco, CA, United States of America

Charles Guan