Methods and apparatus to calibrate electrocardiogram systems

An apparatus comprising:

• a first electrode, a second electrode, and a third electrode;
• first Low Pass Filter (LPF) circuitry having an input coupled to the first electrode and an output;
• second LPF circuitry having an input coupled to the second electrode and an output;
• and
• front-end circuitry having:
• a first input terminal coupled to the output of the first LPF circuitry;
• a first adjustable capacitor coupled to the first input terminal;
• a second input terminal coupled to the output of the second LPF circuitry;
• a first output terminal coupled to the third electrode;
• and
• a second output terminal coupled to controller circuitry.

A method comprising:

• transmitting an excitation signal at an output terminal of front-end circuitry;
• determining an amplitude and phase of a first input signal received at a first input terminal of the front-end circuitry, wherein the first input signal corresponds to first low pass filter (LPF) circuitry;
• determining an amplitude and phase of a second input signal received at a second input terminal of the front-end circuitry, wherein the second input signal corresponds to a second LPF circuitry;
• and
• matching the phase of the second input signal to the phase of the first input signal by changing, responsive to a difference between the amplitudes, a capacitance of an adjustable capacitor coupled to the second input terminal within the front-end circuitry.