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Environmental magnetism compensating device and cathode-ray tube display device
| Details |
Inventors: Chujo, Takeshi;
Assignee: NEC-Mitsubishi Electric Visual Systems Corporation (Tokyo, JP)
Primary Examiner: Lee; Michael H.
Assistant Examiner:
Attorney, Agent or Firm: Birch, Stewart, Kolasch & Birch, LLP
A geomagnetism sensor (2) outputs the vertical magnitude of geomagnetism as a detection signal (Vy). An A-D converter (5) converts the detection signal (Vy) into digital data which in turn is supplied to a CPU (6) together with data from a memory (1). The CPU (6) performs a computation based on a vertical deflection signal (VH), the data from the memory (1) and the detection signal (Vy) to provide parameters (hposi, yvj, vcancel) for determining current values to be supplied to a deflection yoke (13), a convergence correction coil (14) and a beam landing correction coil (15). D-A converters (7-9) convert these parameters into analog signals. Drive circuits (10-12) receives the analog signals provided by conversion to generate current for driving the deflection yoke (13), the convergence correction coil (14) and the beam landing correction coil (15). Image variations under the influence of the vertical component of geomagnetism are automatically corrected. |
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DETAILED DESCRIPTION According to a first aspect of the present invention, an environmental magnetism compensating device comprises: a magnetism sensor for detecting a vertical component of a magnetic environment in which a cathode-ray tube including a deflection yoke, a convergence correction coil and a beam landing correction coil is placed to output a detection signal; an arithmetic unit for determining first to third parameters based on the detection signal; and a driver for supplying current having values set based on the first to third parameters, respectively, to the deflection yoke, the convergence correction coil and the beam landing correction coil.
Preferably, according to a third aspect of the present invention, in the environmental magnetism compensating device of the first aspect, the current supplied to the convergence correction coil varies at two different rates of change for a time period corresponding to one frame in synchronism with a vertical deflection signal for the cathode-ray tube.
Preferably, according to a third aspect of the present invention, in the environmental magnetism compensating device of the first aspect, the current supplied to the convergence correction coil varies at two difference rates of change for a time period corresponding to one frame in synchronism with a vertical deflection signal for the cathode-ray tube.
Preferably, according to a fourth aspect of the present invention, in the environmental magnetism compensating device of the first aspect, the current supplied to the beam landing correction coil is in synchronism with a vertical deflection signal for the cathode-ray tube and has a waveform symmetrical with respect to a midpoint of a time period corresponding to one frame.
Preferably, according to a fifth aspect of the present invention, in the environmental magnetism compensating device of the first aspect, the current supplied to the beam landing correction coil is in synchronism with a vertical deflection signal for the cathode-ray tube and has a waveform asymmetrical with respect to a midpoint of a time period corresponding to one frame
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