Patent ID: 6690339
Filing Date: 2004-02-10
Classification: G09G,H04N

Abstract:
Method for controlling the operating point of a cathode ray tube, to which a video signal is supplied and which includes a control grid that applies a control voltage from an adjusting unit for adjusting the operating point, comprising:a) during a calibration phase using a test image for a set operating point with different brightness and/or contrast values: supplying a test video signal to a cathode ray tube model and to the cathode ray tube; determining an emulated beam current from the video signal using the cathode ray tube model, measuring a beam current of the cathode ray tube, which is proportional to the video signal, calculating first characteristic quantities from the measured beam current and the emulated beam current, storing said first characteristic quantities calculated from the measured and emulated beam currents in a memory location, b) during normal operation, when the cathode ray tube is controlled with picture signals: supplying a picture video signal to the cathode ray tube model and to the cathode ray tube; determining an operational beam current from the picture video signal using the cathode ray tube model, measuring an operational beam current of the cathode ray tube, which is proportional to the picture video signal, calculating second characteristic quantities from the measured operational beam current and the operational emulated beam current; comparing the second characteristic quantities with the first characteristic quantities stored in the memory, and adjusting the control voltage until the second characteristic quantities substantially match the first characteristic quantities stored in the memory during the calibration phase, as a function of said comparison.