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Pincushion Correction by Feedback

IP.com Disclosure Number: IPCOM000091530D
Original Publication Date: 1968-Mar-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Johnson, HW: AUTHOR

Abstract

A pincushion correction circuit for a CRT is shown. The basic sweep generator at the left of the dashed line utilizes constant current source 1 to alternately charge and discharge capacitor 2 through transistors Q4 and Q6 as controlled by transistors Q3 and Q5 respectively. When Q3 and Q6 are on, Q4 and Q5 are shut off and vice versa to control the polarity of the sweep voltage transmitted through buffer 7. The sweep voltage slope is determined by the charging rate of capacitor 2.

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Pincushion Correction by Feedback

A pincushion correction circuit for a CRT is shown. The basic sweep generator at the left of the dashed line utilizes constant current source 1 to alternately charge and discharge capacitor 2 through transistors Q4 and Q6 as controlled by transistors Q3 and Q5 respectively. When Q3 and Q6 are on, Q4 and Q5 are shut off and vice versa to control the polarity of the sweep voltage transmitted through buffer 7. The sweep voltage slope is determined by the charging rate of capacitor 2.

To provide pincushion correction by a first arrangement, the current at points A and B is varied by the circuit at the right of the dashed line to alter the rate of charging of capacitor 2. The correction circuit utilizes transistors Q8, Q9, Q10 and Q11. These serve to bleed current from junction A or, on the opposite half cycle, to supply current to junction B. Thus, on one half cycle, Q10 and Q11 turn on and, on the other half cycle, Q8 and Q9 turn on to vary the current to and from capacitor 2 respectively. The variation in amount is proportional to the sweep voltage required to correct the sweep voltage supplied at connection 12. This technique provides first-order correction.

In the second arrangement of the pincushion correction circuit, connection is made to terminals 13. This circuit provides second-order correction by a square function generator 14. The latter controls the action of transistors Q15 and Q16 which, in turn, bleed current from jun...