An analog bootstrapped biosignal read-out circuit with common-mode impedance two-electrode compensation

In this paper, a two-electrode system performing biomedical signal recordings is presented. Thanks to a continuous balancing of the impedance bridge included in the front-end, the proposed system does not suffer the impedance mismatch of a two-electrode front-end that may affect the biopotential measurement. The rejection of the common mode interference has been improved by including a bootstrapped instrumentation amplifier [showing 133 dB common-mode rejection ratio]. The front-end differential input impedance is very high, being in the worst case 500 MΩ , whereas its common-mode input impedance is 135 kΩ. The proposed architecture also works for an unfavorable input signal-to-noise ratio (SNR) as low as -14 dB. As an example, the electronic interface has been designed and tested for an ECG-like signal. Preliminary tests on a discrete-element electronic prototype have shown the overall system capability of easily recording the heart signal, having evaluated an experimental output SNR of about 32 dB. In addition, the effectiveness of the feedback implementation in restoring the impedance balance has been demonstrated in practice.