Inductive noise cancellation circuit for electromagnetic pickups

An electromagnetic pickup for canceling inductive noise in electrical circuits resulting from external magnetic flux, the pickup comprising

• a first magnetic pickup means responsive to an external magnetic flux for producing a first pickup signal having a first amplitude and a first phase,
• a second magnetic pickup means responsive to the external magnetic flux for producing a second pickup signal having a second amplitude and a second phase,
• a phase-adjustment means coupled to at least one of said first and second magnetic pickups to phase-shift at least one of said first and second pickup signals for reducing the variation in the relative phase with respect to frequency between said first and second pickup signals that results from impedance-differences between said first and second magnetic pickups,
• an amplitude-adjustment means coupled to at least one of said phase-adjustment means, said first magnetic pickup, and said second magnetic pickup to adjust the relative amplitude between said first and second pickup signals for substantially equalizing the amplitudes of inductive noise in said first and second pickup signals, and
• a combining means coupled to at least two of said amplitude-adjustment means, said phase-adjustment means, said first magnetic pickup, and said second magnetic pickup to combine the phase-shifted and amplitude-adjusted first and second pickup signals for producing a combined pickup signal therefrom, wherein the contribution of the external magnetic flux to said first pickup signal is subtracted from the contribution of the external magnetic flux to said second pickup signal, thereby reducing the effects of electromagnetic inductive noise in said combined pickup signal.

An electromagnetic pickup for providing notch-cancellation with respect to frequency for at least one desired frequency of inductive signals in electrical circuits resulting from external magnetic flux, the pickup comprising

• a first magnetic pickup means responsive to an external magnetic flux for producing a first pickup signal having a first amplitude and a first phase,
• a second magnetic pickup means responsive to the external magnetic flux for producing a second pickup signal having a second amplitude and a second phase,
• a combining means coupled to said first and second magnetic pickups for combining said first and second pickup signals to cancel inductive noise at said desired frequency, said combining means comprising an amplitude-adjustment means for equalizing the magnitudes of said first and second pickup signals at said desired frequency and creating unequal magnitudes of said first and second pickup signals away from said desired frequency, and said combining means further comprising a phase-adjustment means for reducing the variation in the relative phase with respect to frequency between said first and second pickup signals that results from impedance-differences between said first and second magnetic pickups and to adjust the phase of at least one of said first and second pickup signals with respect to frequency for providing a predetermined phase-relationship wherein the relative phase between said first and second pickup signals is substantially 180 degrees at said desired frequency, and the relative phase between said first and second pickup signals departs from 180 degrees away from said desired frequency, said first and second pickup signals being combined to optimize cancellation of the external magnetic flux at said desired frequency and minimize cancellation of the external magnetic flux away from said desired frequency.