AD5933

The AD5933 is a high precision impedance converter system solution which combines an on board frequency generator with a 12 Bit 1MSPS ADC. The requency 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 DFT processed by an on-board DSP engine. The DFT algorithm returns a Real (R) and imaginary (I) data word at each output frequency. This magnitude of these data words must be further scaled by calibrated Gain Factor in order to return the actual impedance value at each frequency point. The magnitude of the impedance and relative phase of the impedance at each frequency point along the sweep is easily
calculated using the following equations:
Magnitude= R²+ I² Phase =Tan ^-1(I /R)

To determine the value of the unknown impedance Z(w), generally a frequency sweep is performed. The impedance can be calculated at each point and an impedance profile i.e. frequency vs. magnitude plot can be created. The system allows the user to program a 2 V p-p sinusoidal signal as excitation to an external load. Output voltage excitation ranges of 1 V, 400 mV, 200 mV can also be programmed. The signal is provided on chip using DDS techniques. Frequency resolution of 27 bits (less than 0.1HZ) can be achieved using this method. To perform the frequency sweep, the user must first program the conditions required for the sweep; start frequency, step frequency, and number of incremental points along the sweep into onboard registers. Once the relevant registers have been programmed, a Start Command to the control register is required in order to begin the sweep. To determine the impedance of the load at any one frequency point, Z(w), a measurement system comprised of a transimpedance amplifier, gain stage, and ADC are used to record data. The gain stage for the response stage is 1 or 5. At each point on the sweep the ADC will take 1024 samples and calculate a Discrete Fourier Transform to provide the real and imaginary data for the response signal waveform. The real and imaginary data stored in memory and is available to the user through the 12C interface. The ADC is a low noise; high speed 1 MSPS sampling ADC that operates from 3 V supply. Clocking for both the DDS and ADC signals is provided externally via the MCLK reference clock, which is provided externally from a crystal oscillator or system clock or by use of the internal RC oscillator. The AD5933 is available in a 16 lead SSOP.