Electrodes on double-sided printed circuit board (PCB) to cancel far-held signal

A medical apparatus, comprising:

• a shaft for insertion into an organ of a patient;
• an expandable frame coupled to a distal end of the shaft, the expandable frame extending along a longitudinal axis, wherein the expandable frame comprises a plurality of expandable spines disposed about the longitudinal axis;
• a plurality of diagnostic electrodes, which are disposed on external surfaces of the expandable spines, and which are configured to sense diagnostic signals when in contact with tissue;
• and
• a single reference electrode disposed on substantially the entire internal surface of each of the expandable spines opposite the plurality of diagnostic electrodes,
• wherein the single reference electrode is electrically insulated from the tissue and is configured to sense interfering signals;
• and
• a processor, which is configured to:
• receive the diagnostic signals sensed by each of the plurality of diagnostic electrodes;
• receive the interfering signals sensed by the single reference electrodes;
• and
• calculate corrected diagnostic signals by subtracting the interfering signals from the diagnostic signals.

A method, comprising:

• inserting into an organ of a patient a medical probe, comprising an expandable frame coupled to a distal end of the shaft, the expandable frame extending along a longitudinal axis, wherein the expandable frame comprises a plurality of expandable spines disposed about the longitudinal axis;
• sensing diagnostic signals with a plurality of diagnostic electrodes, which are disposed on the external surfaces of the expandable spines, wherein the plurality diagnostic electrodes are configured to sense diagnostic signals when in contact with tissue;
• sensing interfering signals with a respective plurality of reference electrodes, which are disposed on a surface of the expandable frame directly opposite the diagnostic electrodes, wherein the respective plurality of reference electrodes are electrically connected to each other and electrically insulated from the tissue;
• receiving the diagnostic signals sensed by each of the plurality of diagnostic electrodes;
• receiving the interfering signals sensed by the respective plurality of reference electrodes;
• and
• calculating corrected diagnostic signals by subtracting the interfering signals from the diagnostic signals.