A Single-Channel Amplifier for Simultaneously Monitoring Impedance Respiration Signal and ECG Signal

Physiological signals can reflect the physiological characteristics of the human body and serve as important reference for doctors in clinical diagnosis. Hence, wearable intelligent equipment for physiological signal monitoring has attracted increasing attention. Such equipment must be of a small size and must have low power consumption. To meet these demands, we designed a single-channel amplifier, that can simultaneously acquire the electrocardiograph (ECG) signal and impedance respiration signal. We used oversampling and fast digital lock-in technology to improve the measuring precision of the circuit without increasing the complexity of the circuit. The circuit makes use of the capacitive reactance of a capacitor, which changes with the frequency of the signal; this can meet the different impedance requirements of both the impedance respiratory signal and ECG signal during the measurements. The result of experiments shows that the circuit can obtain high-quality ECG and respiratory waveforms. This circuit can serve as a valuable reference for the design of wearable health monitoring equipment to simultaneously acquire multiple human physiological signals in a signal channel.