Effect of the Electrode Impedance in Improved Buffer Amplifier for Bioelectric Recordings

ESTEBAN VALVERDE; PEDRO ARINI; MARCELO BIAGETTI; GUILLERMO BERTRÁN; RICARDO QUINTEIRO

JOURNAL OF MEDICAL ENGINEERING AND TECHNOLOGY

Taylor & Francis Group

Lugar: Londres; Año: 2004 vol. 28 p. 217 - 222

0309-1902

We analysed the effects of electrode impedance on the transfer response of a one-stage improved buffer amplifier. The electrode DC resistance (Rd) modifies the one-stage buffer transfer response. We found a limit electrode resistance (Rd(lim)) which depends on the transfer damping factor (e). If Rd is lower than 86.5 kOhm, the transfer response of the buffer fulfils American Heart Association (AHA) recommendations, but when Rd is greater than Rd(lim) it must be cautiously weighed up because its influence in the transfer response becomes appreciable. The maximum Rd that can be driven by the buffer is 1.2 MOhm. Higher values do not fulfil AHA recommendations. Therefore, electrodes with higher impedance should not be used with this kind of buffer. In contrast, when this buffer is used to build in an instrumentation amplifier (IA) for bipolar recording, the common-mode rejection ratio (CMRR) is sensitive to the electrode type used.