Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Patent
1985-12-12
1987-11-24
Blum, Theodore M.
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
315403, H01J 2956
Patent
active
047091924
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE ART
The invention is based on a process and a circuit for avoiding of nonlinearities and brightening the picture edges in television pick up tubes.
During the two dimensional scanning of the signal electrode of a television pick up tube with the assistance of an electronic beam only the active picture area had been discharged heretofore. The area of the signal electrode which surrounds this picture area is also charged due to the incoming light, so that during a nonscanning of this surrounding area a charge remains stationary and rapidly accumulates. This charge can only flow off to the active picture area and therefore causes a picture brightening on the four edges of the active picture area. Moreover, the electronic beam is additionally deflected on these four edges due to the accumulated high charge mountains which accumulate in the surrounding area, so that nonlinearities are caused on the picture edges (so-called edge deflection) which are distortions of the picture in the edge area, in the horizontal as well as the vertical direction. Furthermore, these charge mountains cause substantial flicker effects at the left area of the upper edge zone of the signal electrode, in particular with "1/2" pick up tubes.
A process in accordance with the type of the main claim for avoiding these distortions is known from U.S. Pat. No. 4,404,499. Thereby, additional voltages are selectively added for an overscanning to the horizontal and vertical saw tooth deflection signals during the black out intervals, so that the speed of the scanning is increased, for example, doubled or tripled shortly before or shortly after the return movement period. However, it is disadvantageous that the line spacings above the upper and below the lower picture edge are substantially larger than within the active picture area. Thereby, the charges which are present in this surrounding area are only insufficiently discharged, because charges remain stationary between the scanning lines and cause further nonlinearities and picture brightening .
It is therefore an object of the subject invention to provide a process of the aforementioned type with which still present nonlinearities at the proximity of the upper and lower picture edge can be safely avoided.
ADVANTAGES OF THE INVENTION
The process in accordance with the invention with the characterizing features of the main claim is advantageous in that with a relatively low additional expense in timing means all charges above the upper and below the lower picture edge, that is, not only the ones in the area of the predetermined fixed scanning lines of an expanded screen can be neutralized.
Advantageous further embodiments and improvements of the process stated in the main claim is made possible by the measures stated in the subclaims. It is particularly advantageous if the separated positive (or negative) signal amplitudes are invertedly superimposed to the following negative (or positive) amplitudes of the noise signal, whereby a practically complete discharge of the overscanning ranges is made possible.
DRAWING
One exemplified embodiment is illustrated in the drawing and is explained in more detail in the following description. The drawing shows:
FIG. 1 a block diagram for performing the process in accordance with the invention,
FIG. 2 diagrams of some of the signals which occur in FIG. 1,
FIG. 3 the scanning pattern written on the signal electrode,
FIG. 4 a block diagram for another mode of generation of the additional signal.
A difference amplifier 1 in the block diagram in accordance with FIG. 1, has its noninverting input connected to terminal 2 for the saw tooth vertical deflection signal. The pair of vertical deflection coils 4 are connected to output 3 and are grounded via a resistor 6. Different correcting signals (for example, parabola like signals) are applied to the inverting input, whereby only one feed line including a terminal 7 and a resistor 8 is shown by way of example. A feed back through a resistor 11 to the inverting input is provided at connection po
REFERENCES:
patent: 3755707 (1973-08-01), Fremont
patent: 4404499 (1983-09-01), Ryan
patent: 4439713 (1984-03-01), Nakamura et al.
Blum Theodore M.
Issing Gregory C.
Robert & Bosch GmbH
Striker Michael J.
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