Transformer comprising: a substrate having an input side and an output side, the input side being connectable to one section of a medical electrical device, the output side being connectable to another section of the medical electrical device, the substrate having an input ground system and an output ground system which is electrically isolated from the input ground system, the input ground system and the output ground system providing independent continuous return paths for an input signal and an output signal, respectively; a magnetic core mounted to the substrate; a primary winding having a first primary end and a second primary end connected to a positive pad and a negative pad of the input side, the primary winding having a middle portion that wraps around the core, an anterior portion between the first primary end and the middle portion, and a posterior portion between the second primary end and the middle portion; a secondary winding having a first secondary end and a second secondary end connected to a positive pad and a negative pad of the output side, the secondary winding having a middle portion that wraps around the core, an anterior portion between the first secondary end and the middle portion, and a posterior portion between the second secondary end and the middle portion; the core transferring data from the primary winding to the secondary winding using magnetic field coupling; wherein the middle portion of the primary winding and the middle portion of the secondary winding are twisted together; and wherein the anterior portion of the primary winding and the posterior portion of the primary winding are twisted together, while the anterior portion of the secondary winding and the posterior portion of the secondary winding are twisted together. a substrate having an input side and an output side, the input side being connectable to one section of a medical electrical device, the output side being connectable to another section of the medical electrical device, the substrate having an input ground system and an output ground system which is electrically isolated from the input ground system, the input ground system and the output ground system providing independent continuous return paths for an input signal and an output signal, respectively; a magnetic core mounted to the substrate; a primary winding having a first primary end and a second primary end connected to a positive pad and a negative pad of the input side, the primary winding having a middle portion that wraps around the core, an anterior portion between the first primary end and the middle portion, and a posterior portion between the second primary end and the middle portion; a secondary winding having a first secondary end and a second secondary end connected to a positive pad and a negative pad of the output side, the secondary winding having a middle portion that wraps around the core, an anterior portion between the first secondary end and the middle portion, and a posterior portion between the second secondary end and the middle portion; the core transferring data from the primary winding to the secondary winding using magnetic field coupling; wherein the middle portion of the primary winding and the middle portion of the secondary winding are twisted together; and wherein the anterior portion of the primary winding and the posterior portion of the primary winding are twisted together, while the anterior portion of the secondary winding and the posterior portion of the secondary winding are twisted together.