AD5933 報告人:葉榮陞 指導教授:沈毓泰

SYSTEM DESCRIPTION

SYSTEM DESCRIPTION The DFT algorithm returns both a real (R) and imaginary (I) data-word at each frequency point along the sweep. The impedance magnitude and phase are easily calculated using the following equations:

SYSTEM DESCRIPTION

The frequency sweep is fully described by the programming of three parameters Start Frequency :24-bit Register Address 0x82~0x84 Frequency Increment: 24-bit Register Address 0x85~0x87 Number of Increments: 9-bit Register Address 0x88~0x89

FREQUENCY SWEEP COMMAND SEQUENCE 1.Enter standby mode. 2.Enter initialize mode. 3.Enter start frequency sweep mode.

DFT OPERATION A DFT is calculated for each frequency point in the sweep. The AD5933 DFT algorithm is represented by :

TEMPERATURE SENSOR The measurement range of the sensor is −40°C to +125°C. The accuracy within the measurement range is ±2°C.

IMPEDANCE CALCULATION The first step in impedance calculation for each frequency point is to calculate the magnitude of the DFT at that point. The DFT magnitude is given by :

GAIN FACTOR VARIATION WITH FREQUENCY Because the AD5933 has a finite frequency response, the gain factor also shows a variation with frequency. This variation in gain factor results in an error in the impedance calculation over a frequency range.

GAIN FACTOR VARIATION WITH FREQUENCY Alternatively, it is possible to minimize this error by assuming that the frequency variation is linear and adjusting the gain factor with a two-point calibration.

GAIN FACTOR RECALCULATION The gain factor must be recalculated for a change in any of the following parameters: 1.Current-to-voltage gain setting resistor 2.Output excitation voltage 3. PGA gain

MEASURING THE PHASE ACROSS AN IMPEDANCE Formula:

the correct standard phase angle is dependent upon the sign of the real and imaginary component

Thanks for listening