The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jan. 18, 2000
Filed:
Jan. 15, 1998
Nozomu Takahashi, Kanagawa-ken, JP;
Kabushiki Kaisha Toshiba, Kanagawa-ken, JP;
Abstract
A gradation controlled LED display device has an LED array having a matrix of LED chips. The lighting time of each of the LED chips is controlled to display one of gradation levels. The display device has a gradation control circuit, linearity adjusting circuits, and a base-resistance selector that are connected to data lines, which are connected to the LED chips. The gradation control circuit controls the lighting time of each LED chip according to 8-bit display data, to display one of 255 gradation levels. The linearity adjusting circuit determines whether or not five upper bits of given 8-bit display data are all 'zero' and provides a resultant signal. If the resultant signal indicates that the five upper bits are all 'zero', the base-resistance selector selects a large base resistance value, and if any one of the five upper bits is '1', a small base resistance value. In this way, a base resistance value applied to the base of a pnp transistor of a data driver for driving one data line is selected between the large and small values, to sharply turn on and off the pnp transistor at low gradation levels. This arrangement clearly distinguishes the lighting times of low gradation levels from one another and improves the contrast of low gradation levels.