Apparatus for providing vertical as well as horizontal smoothing of convergence correction signals in a digital convergence system

• US 4,422,019 A
• Filed: 07/12/1982
• Issued: 12/20/1983
• Est. Priority Date: 07/12/1982
• Status: Expired due to Term

• Current Assignee: Tektronix Incorporated FITH Drive
• Original Assignee: Tektronix Incorporated (Fortive Corp.)
• Inventors: Meyer, William W.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US06/397,615
• Time in Patent Office: 526 Days
• Field of Search: 315/368, 315/13 C, 358/10
• US Class Current: 315/368.13
• CPC Class Codes: H04N 9/28 Arrangements for convergence or focusing

Abstract

An apparatus of providing vertical smoothing of convergence correction signals in a digital convergence system is disclosed. The surface of a cathode ray tube is subdivided into a matrix including a plurality of intersecting rows and columns and having a plurality of intersections corresponding thereto. A value is assigned to each intersection of a row and a column of said matrix. An electron beam traces a plurality of scan lines within each of the rows of the matrix. For each scan line within a row of the matrix, a convergence correction signal is synthesized using the plurality of values associated with the plurality of intersections in said row. A plurality of horizontal discontinuities are present in the convergence correction signal as a result of the different magnitudes associated with the plurality of values used to synthesize the convergence correction signal. Using conventional filtering techniques, the impact of the horizontal discontinuities in the convergence correction signal may be minimized thereby providing horizontal smoothing of the convergence correction signal. When the electron beam begins tracing the plurality of scan lines in the next, subsequent row of the matrix, a vertical discontinuity is produced, i.e., a gap or an overlap between groups of scan lines traced by the electron beam. The impact of these vertical discontinuities can be minimized by providing vertical smoothing of the convergence correction signal. This vertical smoothing is accomplished by using a linear interpolator to interpolate between values associated with two adjacent, vertically oriented intersections of said matrix, and by progressively changing the magnitude of the convergence correction signal in response thereto. Vertical smoothing of the convergence correction signal is accomplished and the vertical discontinuities between groups of scan lines traced by the electron beams are eliminated.

Claims

1. An interpolator for use in a convergence system, said convergence system developing convergence correction signals for deflecting an electron beam while scanning across the inner surface of a cathode ray tube, the surface of said cathode ray tube being subdivided into a matrix including a plurality of intersecting rows and columns, each row and each column having an address associated therewith, said electron beam tracing within one of the rows and across said columns of said matrix while scanning across the inner surface of said tube, a row address signal and a column address signal being developed corresponding to the address of the row and the column in which said electron beam is scanning, a certain number of scans of said electron beam are actually traced within each of said rows of said matrix, a horizontal sync signal being produced for each of said scans, comprising:

storing means for storing a plurality of values therein corresponding, respectively, to a plurality of intersections associated with the plurality of intersecting rows and columns of said matrix, said storing means generating a first output signal indicative of one of said values associated with one of said intersections and generating a second output signal indicative of another of said values associated with the next, adjacent, vertically oriented intersection relative to the one intersection in response to said row address signal and said column address signal;

converter means responsive to said first and said second output signal from said storing means for developing said convergence correction signal, said convergence correction signal having a signal parameter which changes linearly ranging from a first signal parameter corresponding to said first output signal from said storing means to a second signal parameter corresponding to said second output signal from said storing means, the degree of deflection of said electron beam being proportional to the linear change of said signal parameter associated with said convergence correction signal; and

compensating means responsive to the certain number of said horizontal sync signals for each of said rows of said matrix for developing an output signal indicative of a particular number when the last of said certain number of scans is traced within each of the rows of said matrix, said particular number representing a desired number of scans to be traced by said electron beam within each of said rows of said matrix;

said converter means developing said convergence correction signal in response to said output signal from said compensating means and to the first and second output signals from said storing means.

3. The interpolator of claim 1 wherein said compensating means includes:

binary rate multiplier means energized by the horizontal sync signal for generating a plurality of equally spaced pulses in its output signal in response to a count correction signal that is representative of the difference the selected number scans within each row and the maximum number of scans expected within each row;

delay means for delaying the output signal pulses from the binary rate multiplier means; and

exclusive-or means coupled to receive the horizontal sync signal and the delayed pulses for delay means for causing the signal parameter of the converter means to change in response to both the horizontal sync signal and the delayed pulses.

4. The interpolator of claim 3 wherein said converter means comprises:

line counter means responsive to the output signal from the exclusive-or means for maintaining a count indicative of the number of the scan currently being traced by said electron beam within a said row of the matrix;

first means responsive to said count and to said first output signal from said storing means for developing a first signal, the magnitude of said first signal being a function of said count and said first output signal;

second means responsive to said count and to said second output signal from said storing means for developing a second signal, the magnitude of said second signal being a function of said count and said second output signal,

the magnitude of said first signal decreasing as the count of said line counter means increases,

the magnitude of said second signal increasing as the count of said line counter means increases,

an output terminal of said first means developing said first signal being connected, at a junction, to an output terminal of said second means developing said second signal, said first signal being added to said second signal at said junction to produce a summed signal; and

means responsive to said summed signal for producing said convergence correction signal, said convergence correction signal being a function of said summed signal.

2. The interpolator of claim 2 wherein said converter means comprises:

line counter means responsive to said horizontal sync signal for maintaining a count indicative of the number of the scan currently being traced by said electron beam within a said row of the matrix;

first means responsive to said count and to said first output signal from said storing means for developing a first signal, the magnitude of said first signal being a function of said count and said first output signal;

second means responsive to said count and to said second output signal from said storing means for developing a second signal, the magnitude of said second signal being a function of said count and said second output signal,

the magnitude of said first signal decreasing as the count of said line counter means increases,

the magnitude of said second signal increasing as the count of said line counter means increases,

an output terminal of said first means developing said first signal being connected, at a junction, to an output terminal of said second means developing said second signal, said first signal being added to said second signal at said junction to produce a summed signal; and

means responsive to said summed signal for producing said convergence correction signal, said convergence correction signal being a function of said summed signal.