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Browse Prior Art Database

Focus Coil Regulator And Pin Cushion Correction

IP.com Disclosure Number: IPCOM000098428D
Original Publication Date: 1960-Oct-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 74K

Publishing Venue

IBM

Related People

Smura, EJ: AUTHOR

Abstract

(Image Omitted) The circuit regulates the current applied to the convergence coil 11 of a cathode ray tube 10 as a function of the potential of the high voltage supply 13. The circuit is employed in a Charactron type of CRT display utilizing magnetic focusing. A character is formed by passing the CRT beam through a character matrix 15 so that the diffused electron beam is formed in the shape of the character on the matrix. For a fixed position of the focus coil 11 in the tube 10, the current applied to 11 is proportional to the square root of the potential of the high voltage supply 13. Thus, to produce a uniform focus, a convergence current regulator 17 is utilized to maintain a constant ratio between the potential of supply 13 and the current supplied to the coil 11.

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Focus Coil Regulator And Pin Cushion Correction

(Image Omitted)

The circuit regulates the current applied to the convergence coil 11 of a cathode ray tube 10 as a function of the potential of the high voltage supply 13. The circuit is employed in a Charactron type of CRT display utilizing magnetic focusing. A character is formed by passing the CRT beam through a character matrix 15 so that the diffused electron beam is formed in the shape of the character on the matrix. For a fixed position of the focus coil 11 in the tube 10, the current applied to 11 is proportional to the square root of the potential of the high voltage supply 13. Thus, to produce a uniform focus, a convergence current regulator 17 is utilized to maintain a constant ratio between the potential of supply 13 and the current supplied to the coil 11.

Regulator 17 includes an amplifier 19 whose control grid is connected to a reference battery 20. A pair of serially connected differential amplifiers 21 and 23 receive the output from amplifier 19 and provide stability to the circuit. The output from amplifier 23 is coupled through an output amplifier 25 to the focus coil 11.

Tube 10 has a flat screen which, due to its geometry, tends to distort the shape of the characters in a so called pin cushion distortion. Pin cushion error is given by the formula, R= RO (1 + KRO/2/), where RO is the radius of a circle, R is the enlarged radius and K is a constant. The R in the equation is the expression for the...