AC coupled three op-amp biopotential amplifier with active DC suppression.
A three op-amps instrumentation amplifier (I.A) with active dc suppression is presented. dc suppression is achieved by means of a controlled floating source at the input stage, to compensate electrode and op-amps offset voltages. This isolated floating source is built around an optical-isolated device using a general-purpose optocoupler, working as a photovoltaic generator. The proposed circuit has many interesting characteristics regarding simplicity and cost, while preserving common mode rejection ratio (CMRR) and high input impedance characteristics of the classic three op-amps I.A. As an example, a biopotential amplifier with a gain of 80 dB, a lower cutoff frequency of 0.1 Hz, and a dc input range of +/- 8 mV was built and tested. Using general-purpose op-amps, a CMRR of 105 was achieved without trimmings.
Spinelli
E M
EM
Industrial Electronics, Control and Instrumentation Laboratory (LEICI), Department of Electronics, Universidad Nacional de La Plata (UNLP), CC 91, (1900) La Plata, Argentina. spinelli@venus.fisica.unlp.edu.ar
Mayosky
M A
MA
D000200:Action Potentials; D000669:Amplifiers, Electronic; D016477:Artifacts; D001674:Bioelectric Energy Sources; D017097:Electric Impedance; D004559:Electric Wiring / Q000295:instrumentation*; D055095:Optics and Photonics; D012815:Signal Processing, Computer-Assisted