22.6 A 13-Channel 1.53-mW 11.28-mm 2 Electrical Impedance Tomography SoC Based on Frequency Division Multiplexing with 10× Throughput Reduction

Electrical-impedance tomography (EIT) has been reported as the only viable wearable real-time method for lung imaging [1]. Previous EIT chips generally employ Time-Division Multiplexing (TDM) or as active electrode to facilitate multi-channel read-out [2]–[4], and support a large number of electrodes by sharing a maximum of 6 parallel readout channels per chip. In this paper, we present an EIT-SoC with the following features: 1) early demodulation to relax the bandwidth requirement of the analog front-end, and minimize the impact of motion artifact and DC offset generated at the skin-electrode interface; 2) Frequency-Division Multiplexing (FDM) to combine 13 pairs of I/Q signals into 2 data streams for quantization by 2 $\Delta \Sigma$ Modulators (DSMs); 3) throughput reduction at a compression ratio of 9.75:1; 4) an inverted ‘V-shape’ gain configuration to minimize voltage variations across all channels; and 5) batch spectrum processing for data from all channels with no digital filtering.