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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 twopoint 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