Circuit arrangement for suppressing common-mode interference signals during the measurement of bioelectric signals

A differential voltage measuring system comprising:

• a plurality of measurement paths comprising first and second electrodes, respectively, for detecting a signal present at the respective electrode;
• a first amplifier circuit having a first input and a second input, the first input being electrically connected to the first electrode, the second input being electrically connected to the second electrode, wherein the first amplifier circuit is configured to determine a differential signal from signals present at the first electrode and the second electrode;
• a signal detection circuit configured to detect a differential signal determined by the first amplifier circuit;
• a second amplifier circuit having a first input and a second input, the first input and the second input of the second amplifier circuit being respectively coupled via a capacitance to one electrode of the first electrode and the second electrode;
• an additional current path that is provided with an additional impedance, is coupled to an electrode of the first electrode and the second electrode, and is dimensioned such that transfer functions of individual measurement paths assigned to the individual electrodes are matched to one another.

A differential voltage measuring system comprising:

• two electrodes that are connectable to a patient at an input and make available a respective measurement contact at an output, the two electrodes comprising a first electrode and a second electrode;
• an amplifier circuit having a first input for a first signal from the first electrode, a second input for a second signal from the second electrode, and an output;
• a signal detection unit at the output of the first amplifier circuit;
• a further contact for generating a reference signal on the body of the patient;
• a control unit configured to read signals from the signal detection unit and drive the further contact such that a reference signal corresponding to a measured common-mode voltage is generated on the body of the patient;
• and
• a plurality of protective resistors exclusively between the first electrode and the first input of the amplifier circuit and the second electrode and the second input of the amplifier circuit, such that an impedance of the further contact is minimized.

A method for differentially measuring voltages, the method comprising:

• detecting a first signal with a first electrode and a second signal with a second electrode, the first electrode and the second electrode being connected to a patient at an input and making available a respective measurement contact at an output;
• measuring a common-mode current at a shunt resistor connected to the second electrode;
• and
• determining a corrected differential voltage signal based on measurement values determined.