Browse Prior Art Database

Adaptive Vector End Timing Control

IP.com Disclosure Number: IPCOM000042068D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Related People

McManigal, DF: AUTHOR

Abstract

This article describes a circuit for minimizing intensity variations at vector endpoints in dynamically refreshed displays, minimizing vector generator overhead for very short vectors, and providing dot-size modulation for stored displays. This circuit adapts beam on/off delay times to vector length up to the point where vector length produces constant beam movement rates. Calligraphic (line-drawing) displays exhibit a kind of "inertia" in operation. Beam movement lags beam positioning input signals, with the amount of lag depending largely upon acceleration and deceleration rates. The "inertia" analogy does not hold at constant beam velocities, however, because input-to-deflection lags exist at constant velocities as well as at varying rates.

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Adaptive Vector End Timing Control

This article describes a circuit for minimizing intensity variations at vector endpoints in dynamically refreshed displays, minimizing vector generator overhead for very short vectors, and providing dot-size modulation for stored displays. This circuit adapts beam on/off delay times to vector length up to the point where vector length produces constant beam movement rates. Calligraphic (line-drawing) displays exhibit a kind of "inertia" in operation. Beam movement lags beam positioning input signals, with the amount of lag depending largely upon acceleration and deceleration rates. The "inertia" analogy does not hold at constant beam velocities, however, because input-to-deflection lags exist at constant velocities as well as at varying rates. This deflection lag does not affect displayed data geometry to a great extent, but it does have a marked effect upon vector intensity (the Z-axis). Without some form of compensation, the vector start point will be greatly over-illuminated (even to the point of potential phosphor damage) and the vector end will be invisible. Very high performance calligraphic displays compensate for both geometry and Z-axis distortion by a back-up-and- overshoot technique. This technique sufficiently backs up the display beam to provide uniform beam movement when the actual vector start is reached. Movement continues past the desired vector endpoint to maintain uniform beam movement past the endpoint. Appropriate timing controls switch the beam on and off at the appropriate points, aided by uniform, known rates of beam movement. Direct-view storage tube (DVST) displays operate at lower beam movement rates than these high performance displays, and typically use digital beam positioning controls, rather than the analog controls used in the higher performance units. This results in lower-cost control and more precise beam positioning, but it also renders the back-up-and-overshoot technique quite impractical. Thus, the beam control problem in DVST displays involves acceleration and deceleration between the actual vector endpoints, the effects of which must be minimized through appropriate Z-axis delay controls. The problem is less severe in displaying stored data because each stored spot is either "on" or "off" and cannot exhibit brightness variations except while being written. The DVST, however, exhibits a spot spreading characteristic that depends on the amount of time the display beam dwells on a spot. This characteristic depends primarily upon the fact that the energy distribution across the CRT beam is not uniform, but follows a bell-shaped curve. Vector storage depends upon charge accumulation on the dielectric surface of the phosphor; therefore, turning the beam on at a given spot for a very long time allows even the marginally illuminated particles at the edge of the beam to be stored. This characteristic has been used to advantage in existing display products, but alwa...