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Browse Prior Art Database

Physically Integrated CRT Line Scan Circuit

IP.com Disclosure Number: IPCOM000048077D
Original Publication Date: 1981-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 3 page(s) / 59K

Publishing Venue

IBM

Related People

Gardner, PAE: AUTHOR

Abstract

In order to eliminate or greatly reduce ringing excited by current commutation in a CRT line scan circuit, the active node and ground node connections of the circuit are made to two parallel metal plates separated by a dielectric film. Intercomponent connections are kept to a minimum by mounting the components directly on the active node plate which also acts as a heat sink. By this means, internal inductances causing the ringing are reduced. Further, the inductance associated with capacitor connections may be reduced by using the distributed capacitance of the plates to provide at least a portion of the required circuit capacitance.

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Physically Integrated CRT Line Scan Circuit

In order to eliminate or greatly reduce ringing excited by current commutation in a CRT line scan circuit, the active node and ground node connections of the circuit are made to two parallel metal plates separated by a dielectric film. Intercomponent connections are kept to a minimum by mounting the components directly on the active node plate which also acts as a heat sink. By this means, internal inductances causing the ringing are reduced. Further, the inductance associated with capacitor connections may be reduced by using the distributed capacitance of the plates to provide at least a portion of the required circuit capacitance.

Fig. 1 shows schematically a typical line scan circuit for generating line scan current I(SC) in scan coil 1 in response to input line flyback signals applied to input terminal 2 driving switching element 3. The remainder of the circuit is comprised of negative clamp diode 4, energy store capacitor 5, and S-connection capacitor 6. The switching element 3, diode 4, and capacitor 5 are connected in parallel between the active node and ground node of the circuit. A power supply (not shown) supplies a voltage V(P) to terminal 7 to power the active node through line feed inductance 8. The active node V(A) and ideal scan current I(SC) are shown in Fig. 2.

In use, abrupt changes of current associated with the commutation of current between switching element 3, diode 4 and capacitor 5, together with spurious inductances L3, L4 and L5 associated with these devices cause oscillation trains to be generated. A particular problem is the ringing that occurs when current switches from capacitor 5 to diode 4. These unwanted oscillations distort the early part of the ramp of the line scan waveform, and this is unacceptable in high resolution CRT displays that require a high standard of raster linearity.

The problem is overcome, as shown schematically in Fig. 3 and as a practical implementation in Fig. 4, by forming the active node as one metal plate 9 and the ground node as a second metal plate 10. The plat...