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A Driving Right Leg Circuit or “DgRL” is an electrical circuit which can be added to biological signal amplifiers to reduce Common-mode interference. One of the main issues affecting signal quality in multichannel acquisition systems for bio-potentials (e.g. Electroencephalography, EEG and Electrocardiography, ECG) is the power line interference which can generate common mode voltages on the subject which may be converted to differential signals if the Common Mode Rejection Ratio (CMRR) of the system is insufficient. This is particularly troublesome since the common mode signal can be as high as several hundreds of milliVolts (mV) with the signal to be acquired in the range of tens of microVolts (μV). Many systems employ a Driven Right Leg Circuit (DRL in order to reduce the common-mode interference by trying to fix the patient's common mode to be equal stable with respect to the ground of the acquisition system. However, the level of reduction which can be achieved is limited by the need to keep the circuit stable. With the DgRL, the common-mode is detected by an electrode on the scalp of the patient and drives the isolated ground of the instrumentation which therefore follows the oscillations due to the common mode signal. In this way, even a (single-ended) first stage will see very little common mode at its input, automatically rejecting most of the interference. This is particularly helpful in systems based on active electrodes (where the first amplification stage is integrated on the electrode itself), for which differential acquistion is often impractical.

DgRL can reduce the common mode signal of a factor in excess of 70 dB (at least 30 dB more than a classic DRL loop) and successfully cancel power line interference without any need for differential acquisition and signal post-processing or filtering.