Analysis and Simple Circuit Design of Double Differential EMG Active Electrode

FEDERICO GUERRERO; ENRIQUE M. SPINELLI; MARCELO HABERMAN

IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

Lugar: New York; Año: 2016 vol. 10 p. 787 - 795

1932-4545

In this paper we present an analysis of the voltageamplifier needed for double differential (DD) sEMG measurementsand a novel, very simple circuit for implementing DDactive electrodes. The three-input amplifier that standalone DDactive electrodes require is inherently different from a differentialamplifier, and general knowledge about its design is scarce in theliterature. First, the figures of merit of the amplifier are definedthrough a decomposition of its input signal into three orthogonalmodes. This analysis reveals a mode containing EMG crosstalkcomponents that the DD electrode should reject. Then, the effectof finite input impedance is analyzed. Because there are threeterminals, minimum bounds for interference rejection ratios dueto electrode and input impedance unbalances with two degrees offreedom are obtained. Finally, a novel circuit design is presented,including only a quadruple operational amplifier and a few passivecomponents. This design is nearly as simple as the branched electrodeand much simpler than the three instrumentation amplifierdesign, while providing robust EMG crosstalk rejection and betterinput impedance using unity gain buffers for each electrode input.The interference rejection limits of this input stage are analyzed.An easily replicable implementation of the proposed circuit isdescribed, together with a parameter design guideline to adjust itto specific needs. The electrode is compared with the establishedalternatives, and sample sEMG signals are obtained, acquired ondifferent body locations with dry contacts, successfully rejectinginterference sources.