Measuring a Grounded Impedance Profile Using the AD5933 Application Note (AN-847)

INTRODUCTION This application note describes the circuit architecture and details required to measure the impedance profile of a grounded sensor using the AD5933 impedance-to-digital converter. The AD5933 is a high precision impedance converter system (see Figure 1) that combines an on-board frequency generator with a 12-bit, 1 MSPS, analog-to-digital converter (ADC). The frequency generator allows an external complex impedance to be excited with a known frequency. The response signal from the impedance is sampled by the on-board ADC, and a discrete Fourier transform (DFT) is processed by an on-board DSP engine. The DFT algorithm returns a real (R) and imaginary (I) data-word at each output frequency. The magnitude of the impedance and relative phase of the impedance at each frequency point along the sweep are easily calculated using Equation 1 and Equation 2.