Design and Implementation of a DSP-based Digital Phase Sensitive Demodulation for an EIT System

Electrical Impedance Tomography (EIT) is a non-invasive imaging method that can generate image of impedance distribution inside an object. In this imaging method, measured voltages are complex quantities that contain real and imaginary parts. To increase the accuracy of image reconstruction in EIT systems, it is necessary to utilize both real and imaginary parts of measured voltages. Phase sensitive demodulator can accurately specify the two parts of measured voltages. In this paper, a digital phase sensitive demodulator (DPSD) has been designed and implemented using a DSP board. Floating point 32-bit arithmetic with high speed of 225 MHz of the DSP core allows this digital demodulator to accurately measure real and imaginary parts of measured voltages with a desired SNR in an EIT system. This paper describes the theory and implementation of DPSD on a TMS320C6713 DSP board. Next, simulation data generated by the Code Composer Studio software and the data of an EIT phantom are applied to the DPSD. The simulation data results show a 0.12 degree phase error and a 0.37 % amplitude error with high SNR of 130.6 dB. The EIT phantom results present the 0.76 degree phase error and the 0.91 % amplitude error.