| 摘要 |
A horizontal focus circuit in an image display for improving the focus characteristics at the edges of a planar CRT screen or a CRT screen used in a multi-sync mode. The horizontal focus circuit comprises a horizontal output portion for generating a flyback pulse, a horizontal dummy transformer for transforming the flyback pulse supplied from the horizontal output portion, a parabolic output circuit for generating a parabolic signal from the transformed flyback pulse supplied from the horizontal dummy transformer, a voltage circuit for rectifying and integrating the transformed flyback pulse supplied from the horizontal dummy transformer to generate a direct current (DC) voltage, a mode selection portion for generating a mode selection signal according to the sync frequency, a differential amplifying circuit for combining the mode selection signal supplied from the mode selection portion and the parabolic signal supplied from the parabolic output circuit, leveling up the DC voltage of the combined signal by a DC voltage supplied from the voltage circuit, and amplifying the combined and leveled-up parabolic signal, and a cascode amplifying circuit for controlling and amplifying the amplitude and frequency characteristics of the parabolic signal supplied from the differential amplifying circuit and supplying the amplified parabolic singal to a focusing grid of the CRT.
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