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Incremental Deflection Circuit

IP.com Disclosure Number: IPCOM000089925D
Original Publication Date: 1968-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Greeson, JC: AUTHOR [+2]

Abstract

In one form of cathode ray tube alphanumeric display, the deflection requirement is for equal steps for horizontal and vertical deflection with retrace at the end of each line. A method of obtaining incremental deflection, accomplished by adding an increment of charge to a capacitor for each current step, operates as follows. When a positive current pulse is applied to input terminal 11, capacitor 13, across deflection amplifier 15, is charged to a value Q=IT.

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Incremental Deflection Circuit

In one form of cathode ray tube alphanumeric display, the deflection requirement is for equal steps for horizontal and vertical deflection with retrace at the end of each line. A method of obtaining incremental deflection, accomplished by adding an increment of charge to a capacitor for each current step, operates as follows. When a positive current pulse is applied to input terminal 11, capacitor 13, across deflection amplifier 15, is charged to a value Q=IT.

A constant current source comprising transistors 17 and 19 is connected between +3 and -3 volt sources. The positive current pulse applied to input terminal 11 back biases diode 21, thus presenting a high impedance to the input of amplifier 15 for the period of the pulse. When the current pulse drops, the high impedance input is removed, the constant current source adds another increment of charge across capacitor 13 and increases the output from amplifier 15 by the same amount. This operation is repeated for as many deflection increments as required by the specific display.

To reset the circuit, capacitor 13 is discharged as follows. When capacitor 13 is being incrementally charged, the input level of terminal 23 is down, transistor 25 is nonconducting and the voltage across the input to amplifier 27 corresponds to the charge across capacitor 13. Diodes 29 and 31 comprise a logical input And to transistor 25. Diode 33 provides noise immunity and isolates transistor 25 during...