Rejection of the common-mode signal component in the measurement of bioelectric signals

A differential voltage measuring system comprising:

• a first measuring path comprising a first electrode, wherein an input of the first measuring path is connected to a patient and an output of the first measuring path provides a first measuring contact;
• a second measuring path comprising a second electrode, wherein an input of the second measuring path is connected to the patient and an output of the second measuring path provides a second measuring contact;
• an amplifier circuit comprising a first input electrically connected to the first measuring path, a second input electrically connected to the second measuring path, and an output;
• a signal detection unit at the output of the amplifier circuit;
• an additional path comprising a contact with the patient, the additional path having a driver circuit for a right leg, a shunt resistor with a known resistance value, wherein the additional path is connected between an additional contact and the driver circuit;
• and
• a voltage measuring device connected parallel to the shunt resistor and having an electrical voltage dropping across the shunt resistor, the voltage measuring device configured to measure a current flowing between the additional contact and the driver circuit.

A differential voltage measuring system comprising:

• a first measuring path comprising a first electrode, wherein an input of the first measuring path is connected to a patient and an output of the first measuring path provides a first measuring contact;
• a second measuring path comprising a second electrode, wherein an input of the second measuring path is connected to the patient and an output of the second measuring path provides a second measuring contact;
• an amplifier circuit comprising a first input electrically connected to the first measuring path, a second input electrically connected to the second measuring path, and an output;
• a signal detection unit at the output of the amplifier circuit;
• and
• a potential measuring unit designed for determining an average value from a potential at the first measuring path between the first electrode and the first input of the amplifier circuit and a potential at the second measuring path between the second electrode and the second input of the amplifier circuit,
• wherein the potential measuring unit comprises two parallel-connected potential measuring paths and an amplifier circuit having a first input, a second input, and an output, wherein the first input of the amplifier circuit of the potential measuring unit is electrically connected to the branching point of the parallel-connected potential measuring paths and the second input of the amplifier circuit of the potential measuring unit is electrically connected to a reference potential, and
• wherein the reference potential is the potential of an electrocardiogram input circuit.