| 摘要 |
PURPOSE:To obtain the correction of a high precision through a comparatively simple circuit constitution by obtaining the approximate expression of the correction curve of a two dimensional higher order function from the convergence correction quantities of plural points on a CRT picture field, and generating approximately the analog signal waveform of the two dimensional higher order from the coefficients of this approximate expression. CONSTITUTION:In an arithmetic circuit 1, the coefficients k1-k9 of two dimensional second order function expression are obtained from the convergence correction quantities a1-a9 by an arithmetic operation. Next, from the convergence correction quantities a1-a9 of nine points, shown in a figure, a correction waveform is generated through the approximate correction expression, expressed by the two dimensional second order function. The arithmetic operation is performed by the arithmetic circuit 1 and the data of the coefficients k1-k9 obtained by this operation are stored in a digital memory 2. These data are converted into analog voltages by a D/A converter 3. Then, by adding the outputs of an addition circuit 12, a multiplication circuit 17 and the multiplication circuit 18 by the addition circuit 19, the two dimensional second order function waveform is obtained. An output circuit 20 allows a convergence correction current waveform, expressed by the two dimension second order function to flow in a correction coil 21.
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