A 2.79-mW 0.5%-THD CMOS current driver IC for portable electrical impedance tomography system

A low-power and high-accuracy current driver IC is proposed for portable electrical impedance tomography (EIT) systems. The proposed IC supports active electrode configuration and has three key features. First, high output impedance current driver is implemented with phase compensation scheme through a delay-locked loop (DLL) to significantly alleviate a phase shift and a required power consumption in the driver. Second, low-power pseudo-sine wave generator is used not only for a low-harmonic distortion but also for a flexible injection frequency utilization. Through the proposed quantization scheme, total harmonic distortion (THD) is reduced by 35%, achieving THD less than 0.5%. Third, the calibration unit is proposed to compensate injection-current amplitude variations among active electrodes. As a result, the proposed current driver IC guarantees more than 1MΩ output impedance over a wide range of injection current up to 400pA and operating frequency from 1kHz to 5MHz, only consuming 2.79mW.