A voltage sensing system includes input impedance balancing for electrocardiogram
(ECG) sensing or other applications, providing immunity to common-mode noise signals
while capable of use with two electrodes. Signals are received at first and second
electrodes having associated impedances. An impedance circuit includes a feedback
controller that adjusts an effective impedance associated with the second electrode
based on a difference signal, a common mode signal, a phase-shifted (e.g., quadrature
common mode) signal, and an impedance associated with the first electrode. As a
result, signals associated with each electrode undergo a similar degree of gain/attenuation
and/or phase-shift. This reduces common mode noise and enhances the signal-to-noise
characteristics of a desired ECG or other output signal, without requiring the
use of more than two electrodes.
