Passive neutralization of myoelectric interference from neural recording tripoles

In this paper, we present a simple passive technique for removing myoelectric interference in neural recording systems using tripolar electrodes. Imbalance is simply unavoidable with the conventional quasi-tripole (QT) amplifier and this technakshnique is based on a modified version of the QT, which sees the tripole as a bridge that can be balanced by adding impedance to one of the outer electrodes. We show that parallel resistance and capacitance is better than a series combination for use at all frequencies, and that with a tripole that was intentionally made imbalanced, by an amount that we measure as 3%, the interference can be reduced about 10-fold. It is important to null the interference at low frequencies, in the electromyography (EMG) band, to get the best improvement. Common-mode interference can also be reduced by appropriate trimming if necessary.