Ambient electromagnetic field compensating magnetic pick-up circuit for integrated drive generators

A magnetic pick-up circuit operating within an enclosure adjacent a single source emanating an ambient electromagnetic field, comprising:

• a frame having a first bore and a second bore parallel with said first bore;
• a permanent magnet providing a flux field and a first coil disposed within said first bore, said first coil responsive to said ambient electromagnetic field emanating from said single source and modulation of said flux field;
• a second coil disposed within said second bore responsive to said ambient electromagnetic field, positioned such that wavefronts of said ambient electromagnetic field simultaneously impinge on said first and second coils and differentially connected to said first coil to thereby ensure that a signal induced by said ambient electromagnetic field in said first coil is cancelled by a signal induced by said ambient electromagnetic field in said second coil;
• and
• means coupled to said first coil and said second coil for providing an output signal representative of modulation of said flux field, which output signal is free from distortion due to said ambient electromagnetic field.

A method for providing a distortion-free output signal representative of the modulation of a flux field within an enclosure adjacent a single source emanating an ambient electromagnetic field, comprising the steps of:

• inducing a first signal and a modulated flux signal in a first coil, said first signal representing pulsation of said ambient electromagnetic field emanating from said single source and said modulated flux signal representing the modulation of said flux field;
• substracting from said first signal a second signal induced in a second coil positioned such that wavefronts from said ambient electromagnetic field simultaneously impinge on said first and second coils, said second signal representing pulsation of the ambient electromagnetic field, to thereby ensure that said second signal nullifies said first signal cancelling distortion in an output signal due to said ambient electromagnetic field;
• and
• producing said output signal representative of the modulation of only said flux field thereby eliminating distortion due to said ambient electromagnetic field.