Design of a Wearable Three-Channel Transthoracic Bioimpedance Spectroscopy Front-End with Synchronized ECG Acquisition

Transthoracic bioimpedance spectroscopy is a promising wearable sensing modality for tracking impedance based physiological changes, but practical wearable acquisition is limited by the lack of synchronized cardiac electrical information. This paper presents a portable three-channel thoracic bioimpedance front-end with synchronized electrocardiogram acquisition. The system integrates a DDS based sinusoidal excitation source, single-supply analog conditioning, a Tietze-type VCCS, multiplexed tetrapolar electrode selection, lead-off detection, GPD, an ECG analog front-end, microcontroller control, Bluetooth communication, and battery-powered operation. The excitation circuit generates 100 frequency points from 1 kHz to 1 MHz with an approximately 290μA current and less than 5 percent variation across the measured band. Based on the evaluated data, the impedance mean absolute percentage errors were 3.9±0.24%, 5.2±0.32%, and 5.72±0.5% for Channels 1–3, respectively. The corresponding phase mean absolute errors were 1.12±0.5◦, 1.08±0.7◦, and 1.4±0.65◦. Position-matched Nyquist trajectories further confirmed preservation of the resistive and reactive impedance components for all three channels. The integrated ECG path produced clearly identifiable R−peaks over a 30s recording. These results demonstrate a compact, single supply platform capable of acquiring validated multi-frequency BioZ data from all three transthoracic paths together with synchronized cardiac electrical timing.