Two-electrode non-differential biopotential amplifier

Abstract

A circuit is proposed for a non-differential two-electrode biopotential amplifier, with a current source and a transimpedance amplifier as a potential equaliser for its inputs, fully emulating a differential amplifier. The principle of operation is that the current in the input of the transimpedance amplifier is sensed and made to flow with the same value in the other input. The circuit has a simple structure and uses a small number of components. The current source maintains balanced common-mode interference currents, thus ensuring high signal input impedance. In addition, these currents can be tolerated up to more than 10 microA per input, at a supply voltage of +/- 5 V. A two-electrode differential amplifier with 2 x 10 Mohm input resistances to the reference point allows less than 0.5 microA per input. The circuit can be useful in cases of biosignal acquisition by portable instruments, using low supply voltages, from subjects in areas of high electromagnetic fields. Examples include biosignal recordings in electric power stations and electrically powered locomotives, where traditionally designed input amplifier stages can be saturated.

Estimation of stray coupling capacitances in biopotential measurements

“…Holter systems, as current wearable monitoring devices, must be able to work in very aggressive interference environments. The knowledge of the EMI conditions that biopotential amplifiers can be subject to, is particularly important for designing these portable devices; in order to obtain interference-free biomedical signals [6] and to prevent amplifier saturation because of high EMI levels [2,4].…”

Simple two-electrode biosignal amplifier

“…The moderately high differential input impedance of this amplifier would limit its application in cases where special, very high electrode-skin impedance electrodes are necessary and/or a high level of common mode interference has to be tolerated. In these cases, previously published designs are more convenient (DOBREV, 2002;2004;DOBREV and DASKALOV, 2002).…”

“…A circuit for a two-electrode, non-differential amplifier was developed (DOBREV, 2002) quasi-equivalent to the differential amplifier described by DOBREV and DASKALOV (2002). Because the body as signal source is floating and, in addition, the modern biopotential amplifiers are isolated, it is possible to drive actively one of the electrodes to the circuit common potential and thus to balance the flowing interference currents.…”

Two-electrode low supply voltage electrocardiogram signal amplifier

“…The last requirement corresponds to interference level, which commonly occurs in a hospital room environment, according to our previous experience (DOBREV and DASKALOV, 2002;DOBREV, 2002). Even with a battery-supplied amplifier, input common mode currents can often reach 1.5 gA per input.…”