Key result
Three op-amp instrumentation amplifier with active dc suppression achieves a CMRR of 105 without trimmings.
Why the study?
A three op-amps instrumentation amplifier with active DC suppression is proposed to compensate electrode and op-amps offset voltages while preserving CMRR and high input impedance.
The proposed three op-amp instrumentation amplifier provides active DC suppression with high CMRR and input impedance using simple, low-cost components.
May enable low-cost, high-fidelity biopotential amplifiers; leaves open clinical validation and integration.
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.
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A 2000 study studied this question. AC coupled three op-amp biopotential amplifier with active DC suppression was evaluated. A three op-amps instrumentation amplifier with active dc suppression achieved a CMRR of 105 without trimmings, a gain of 80 dB, and a lower cutoff frequency of 0.1 Hz.
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