US 4,063,134 A · Raster distortion correction circuit

Abstract

A raster distortion correction circuit for correcting both pincushion distortion and trapezoidal distortion of a raster on a cathode ray tube. A parabolic-shaped signal and a sawtooth-shaped signal, both having frequencies equal to the vertical deflection frequency, are supplied to the correction circuit. The amplitude and polarity of the sawtooth-shaped signal is selectively adjusted, and the adjusted sawtooth-shaped signal is combined with the parabolic-shaped signal and supplied to a current modulator. A horizontal deflecting current flows through the modulator and is thus modulated by the combined parabolic-shaped signal and adjusted sawtooth-shaped signal, the modulated horizontal deflecting current being supplied to a horizontal deflection coil included in the horizontal deflection circuit for the cathode ray tube. The parabolic-shaped signal component corrects the pincushion distortion and the adjusted sawtooth-shaped component corrects the trapezoidal distortion.

Claims14

Dependent claims

For use with a cathode ray tube of the type having trapezoidal distortion of the raster caused by beam mislanding correction means adapted to correct for beam mislanding caused by the magnetic field of the earth, a raster distortion correction circuit for correcting both pincushion distortion and said trapezoidal distortion of said raster, comprising:

means for supplying a periodic parabolic signal having a parabolic waveform and a frequency equal to the vertical deflection frequency of said cathode ray tube;
means for supplying plural periodic sawtooth signal components, each having a sawtooth waveform and a frequency equal to said vertical deflection frequency of said cathode ray tube;
adjusting means for receiving said sawtooth signal components and producing an output sawtooth signal as a function of said supplied sawtooth signal components, said output sawtooth signal having adjustable amplitude and polarity for correcting said trapezoidal distortion caused by said beam mislanding correction means;
a horizontal deflection circuit including a horizontal deflection coil for passing a horizontal deflecting current through said horizontal deflection coil at the horizontal deflection frequency of said cathode ray tube;
and
modulating means for receiving both said parabolic signal and said output sawtooth signal to modulate said horizontal deflecting current therewith, whereby said parabolic signal corrects said pincushion distortion and said adjusted sawtooth signal corrects said trapezoidal distortion.

3 more elements

For use with a cathode ray tube of the type having pincushion distortion of the raster on its viewing screen and trapezoidal distortion of said raster caused by beam mislanding correction means, the latter means being adapted to correct for beam mislanding caused by the magnetic field of the earth, said mislanding correction being a function of the compass direction in which said viewing screen faces, apparatus for correcting both said pincushion distortion and said trapezoidal distortion of said raster, comprising:

first means for supplying a periodic parabolic signal having a parabolic waveform superposed on a first periodic sawtooth signal having a sawtooth waveform, said parabolic and first sawtooth signals each having a frequency equal to the vertical deflection frequency of said cathode ray tube;
second means for supplying a second periodic sawtooth signal having a sawtooth waveform and a frequency equal to said vertical deflection frequency;
variably adjustable control means coupled to said first and second means for receiving said parabolic signal and said first and second sawtooth signals and for variably adjusting the ratio between said sawtooth signals to produce a control signal having a parabolic signal component and a sawtooth signal component of amplitude and polarity proportional to said ratio;
a horizontal deflection circuit including a horizontal deflection coil for passing a horizontal deflecting current through said horizontal deflection coil;
and
variable impedance means responsive to said control signal to proportionately vary the impedance thereof for correspondingly modulating the horizontal deflecting current flowing therethrough.

3 more elements

Dependencies are inferred from the claim text.

Raster distortion correction circuit

Life of this patent

Raster distortion correction circuit

Life of this patent

Abstract

Claims14