Browse Prior Art Database

Pulse Stretching for CRT Display Visibility

IP.com Disclosure Number: IPCOM000049236D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Chase, BO: AUTHOR

Abstract

With a high density CRT raster display video amplifier rise time is critical to the definition of the characters or graphics. This is particularly the case with displays not operated in pulsed mode where single pel (picture element) vertical strokes can be less bright than continuous line horizontal strokes. The problem is overcome by using standard logic delay techniques to stretch the video pulses and thus the pels by a predetermined amount. The logic is equally effective for stretching positive-going pulses for display in normal mode or negative-going pulses for display in reverse mode. In images where both normal and reverse mode are used together, the nature of the required pulse stretching can be defined by character attributes or determined on the fly by integration of the pel content.

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Pulse Stretching for CRT Display Visibility

With a high density CRT raster display video amplifier rise time is critical to the definition of the characters or graphics. This is particularly the case with displays not operated in pulsed mode where single pel (picture element) vertical strokes can be less bright than continuous line horizontal strokes. The problem is overcome by using standard logic delay techniques to stretch the video pulses and thus the pels by a predetermined amount.

The logic is equally effective for stretching positive-going pulses for display in normal mode or negative-going pulses for display in reverse mode. In images where both normal and reverse mode are used together, the nature of the required pulse stretching can be defined by character attributes or determined on the fly by integration of the pel content.

A simple circuit for performing pulse stretching is shown in the figure. The input video data at input terminal 1 is passed by exclusive OR-gate 2, inverted or unchanged, depending on whether the display is operating in normal or reverse video mode. The switching of the OR-gate 2 into invert mode is achieved by raising the level of a signal applied to its switching input from terminal 3. In this example, negative-going pulses representing information for display in reverse mode are transmitted unchanged by OR-gate 2, whereas positive-going pulses representing information for display in normal mode are inverted. The level of the sig...