Browse Prior Art Database

Voltage Controlled Asymmetric Linearity

IP.com Disclosure Number: IPCOM000035174D
Original Publication Date: 1989-Jun-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Stone, CD: AUTHOR

Abstract

In a CRT display, an S-shaped current waveform is required through the vertical yoke to provide an undistorted character display. This shaped ramp is generated by adding an exponential charging waveform to an integrated ramp waveform. In the circuit disclosed a variable DC voltage input is used to control the level of correction applied to a vertical ramp generator. The DC voltage may be set up by electronic control.

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Voltage Controlled Asymmetric Linearity

In a CRT display, an S-shaped current waveform is required through the vertical yoke to provide an undistorted character display. This shaped ramp is generated by adding an exponential charging waveform to an integrated ramp waveform. In the circuit disclosed a variable DC voltage input is used to control the level of correction applied to a vertical ramp generator. The DC voltage may be set up by electronic control.

This shaped waveform can be produced by adding an exponential charging waveform and an integrated ramp waveform. The degree of shaping required is wholly determined by the geometry of the CRT and so can be fixed for a particular CRT type. If the relative proportions of the two waveforms are not quite correct, then the top half of the screen becomes a different height to the bottom half. This is called asymmetric linearity error. For this reason, there is usually an adjustment for one of the waveforms, and it is usually the integrated ramp waveform that is chosen as affecting the exponential charging waveform has a large effect on height. A common way of adjusting is by using a variable resistor as per VR1 in Fig. 1.

If the monitor is being designed to be set up purely electrically, for example, in a digitally set monitor where DACs are used for all adjustments, then a circuit is required that can set vertical asymmetric linearity by adjusting a voltage and not by varying a resistor. The circuit described in Fig...