AD5933YRSZ Analog Devices Inc, AD5933YRSZ Datasheet - Page 17

• Manufacturer Part Number: AD5933YRSZ
• Description: IC NTWK ANALYZER 12B 1MSP 16SSOP
• Manufacturer: Analog Devices Inc

Specifications of AD5933YRSZ

• Resolution (bits): 12 b
• Master Fclk: 16.776MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Supply Voltage Range: 2.7V To 5.5V
• Operating Temperature Range: -40°C To +125°C
• Digital Ic Case Style: SSOP
• No. Of Pins: 16
• Frequency Max: 0.1MHz
• Termination Type: SMD
• Pin Count: 16
• Screening Level: Automotive
• Package Type: SSOP
• Filter Terminals: SMD
• Rohs Compliant: Yes
• Communication Function: Network Analyzer
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-AD5933EBZ - BOARD EVALUATION FOR AD5933
• Tuning Word Width (bits): -
• Lead Free Status / Rohs Status: Compliant
• Other names: AD5933BRSZ; Q2204656A

IMPEDANCE CALCULATION
MAGNITUDE 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
where:
R is the real number stored at Register Address 0x94 and Register
Address 0x95.
I is the imaginary number stored at Register Address 0x96 and
Register Address 0x97.
For example, assume the results in the real data and imaginary
data registers are as follows at a frequency point:
To convert this number into impedance, it must be multiplied by
a scaling factor called the gain factor. The gain factor is calculated
during the calibration of the system with a known impedance
connected between the VOUT and VIN pins.
Once the gain factor has been calculated, it can be used in the
calculation of any unknown impedance between the VOUT and
VIN pins.
GAIN FACTOR CALCULATION
An example of a gain factor calculation follows, with the following
assumptions:
Then typical contents of the real data and imaginary data registers
after a frequency point conversion are:
Real data register = 0x038B = 907 decimal
Imaginary data register = 0x0204 = 516 decimal
Output excitation voltage = 2 V p-p
Calibration impedance value, Z
PGA Gain = ×1
Current-to-voltage amplifier gain resistor = 200 kΩ
Calibration frequency = 30 kHz
Real data register = 0xF064 = −3996 decimal
Imaginary data register = 0x227E = +8830 decimal
Gain
Magnitude
Magnitude
Magnitude
Factor
=
=
=
=
⎛
⎜
⎝
R
(
(
Admittance
907
−
2
3996
+
Code
2
I
+
2
)
516
2
+
(
2
8830
)
⎞
⎟
⎠
=
=
1043
CALIBRATION
⎛
⎜
⎜
⎝
)
Impedance
Magnitude
2
=
.
506
9692
1
= 200 kΩ
.
106
⎞
⎟
⎟
⎠
Rev. C | Page 17 of 44
IMPEDANCE CALCULATION USING GAIN FACTOR
The next example illustrates how the calculated gain factor
derived previously is used to measure an unknown impedance.
For this example, assume that the unknown impedance = 510 kΩ.
After measuring the unknown impedance at a frequency of
30 kHz, assume that the real data and imaginary data registers
contain the following data:
Then the measured impedance at the frequency point 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. Figure 22 shows an impedance profile based on
a single-point gain factor calculation. To minimize this error, the
frequency sweep should be limited to as small a frequency range
as possible.
Figure 22. Impedance Profile Using a Single-Point Gain Factor Calculation
Real data register = 0xFA3F = −1473 decimal
Imaginary data register = 0x0DB3 = +3507 decimal
Impedance
Gain
Magnitude
101.5
101.0
100.5
100.0
99.5
99.0
98.5
Factor
54
VDD = 3.3V
CALIBRATION FREQUENCY = 60kHz
T
MEASURED CALIBRATION IMPEDANCE = 100kΩ
A
= 25°C
=
=
=
=
Gain
515
56
⎛
⎜
⎜
⎜
⎜
⎝
((
9692
200
−
.
819273
1473
Factor
1
.
k
106
58
Ω
)
FREQUENCY (kHz)
2
⎞
⎟
⎟
⎟
⎟
⎠
+
1
×
×
=
10
(
Magnitude
3507
1
515.819
60
−
12
)
×
2
)
3802
=
62
×
3802
10
.
863
-
12
.
863
Ω
64
=
509
AD5933
.
791
66
k
Ω