Patent ID: 7183713

Claim:
A magnetic field compensation apparatus, comprising: a first digital-to-analog converter responsive to a digitally encoded signal containing magnetic field compensation information; for generating a first analog signal containing the magnetic field compensation information from said digitally encoded signal; a magnetic field compensation winding positioned on a cathode ray tube; an amplifier responsive to said first analog signal and having an output that is coupled to said magnetic field compensation winding for producing a current in said magnetic field compensation winding, said current producing a magnetic field in a beam path of said cathode ray tube that compensates for an ambient magnetic field; and a second digital-to-analog converter for generating a second analog signal that is coupled to an input of said amplifier that varies said current in accordance with said second analog signal; wherein said compensation winding is coupled to a source of a supply voltage, wherein a polarity of said current varies in accordance with a difference between an output voltage of said amplifier and said supply voltage and wherein a polarity of said amplifier output voltage remains the same both when said current is at a first polarity and when said current is at a polarity that is opposite to said first polarity.