A FPGA-based sweep-frequency voltage source for EIT system

A FPGA-based sweep-frequency voltage source for EIT is designed in this paper. There are three methods for generating sine signal for EIT, including the special function generator, the general purpose chip, and the ordinary oscillator circuit. The special function generator has some inherent characteristics of wide-band frequency and stable output. But the range of frequency is so broad that it is difficult to be changed into suitable output signal for acquiring the tissue characteristic in a very narrow band. The oscillator circuit possesses simple structure and low cost, but with the fatal flaw of an unstable output signal and a lot of inconvenience for adjusting frequency. The general purpose chip such as field programmable gate array is an excellent product in stability and adjustability for sweep-frequency EIT system. In EIT system, the range of frequency is between 1 KHz and 1 MHz. And in order to ensure the phase resolution and the up-limit frequency, a new method to expand the frequency was introduced. Then, a sweep-frequency digital voltage source was designed with the new method to acquire a broad-band output. Finally, it analyzed the frequency spectrum of output signal.