Capacitive ECG Circuit with Fast Recovery for Continuous Exercise Monitoring

To detect electrophysiological signals on clothing through capacitive electrocardiogram(cECG), the front-end amplifier must possess a very high impedance to effectively capture ECG information. However, the trade-off for high impedance and capacitive coupling is the introduction of large time constants, making cECG more susceptible to interference from electrostatic charges and motion artifacts. In instances where artifacts reach levels sufficient to saturate the preamplifier, a considerable amount of time (up to tens of seconds) is required to restore the circuit to its normal detection voltage. During this interval, biopotential signals are irretrievably lost.To address this challenge, this paper proposes a cECG circuit featuring a fast recovery(FR) function. This function operates at the front stage, using the over flow signal of a single-lead heart rate monitor IC(AD8232). It elevates the potential high through the T-network bias resistor connected to the positive phase input terminal of the front stage, inducing the front stage follower circuit to transition from a saturated state while preserving a high input impedance. The time constant of the circuit underwent testing, and the feasibility of this method was verified through simulations of the saturation state and assessments of the circuit's fast recovery during actual movement.