AD5934 datasheet(16/32 Pages) AD

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AD5934

Rev. 0 | Page 16 of 32

GAIN FACTOR TEMPERATURE VARIATION

The typical impedance error variation with temperature is in the

order of 30 ppm/°C. Figure 21 shows an impedance profile with a

variation in temperature for 100 kΩ impedance using a 2-point

gain factor calibration.

101.5

98.5

FREQUENCY (kHz)

101.0

100.5

100.0

99.5

99.0

+125

°C

+25

°C

–40

°C

VDD = 3.3V

CALIBRATION FREQUENCY = 60kHz

MEASURED CALIBRATION IMPEDANCE = 100k

Figure 21. Impedance Profile Variation with Temperature Using a 2-Point Gain

Factor Calculation

IMPEDANCE ERROR

Minimizing the impedance range under test optimizes the

AD5934 measurement performance. Below are examples of the

AD5934 performance when operating in the six different

impedance ranges. The gain factor is calculated with a precision

resistor in each case.

Range 1 (0.1 kΩ to 1 kΩ)

Output excitation voltage = 2 V p-p

Calibration impedance value, ZCALIBRATION = 100 Ω

PGA gain = ×1

Supply voltage = 3.3 V

Current-to-voltage amplifier gain resistor = 100 Ω

FREQUENCY (kHz)

100

RFB = 0.1k

CALIBRATION IMPEDANCE = 0.1k

TA = 25°C

0.5k

Figure 22. Range 1: Typical % Impedance Error over Frequency

Range 2 (1 kΩ to 10 kΩ)

Output excitation voltage = 2 V p-p

Calibration impedance value, ZCALIBRATION = 1 kΩ

PGA gain = ×1

Supply voltage = 3.3 V

Current-to-voltage amplifier gain resistor = 1 kΩ

2.0

FREQUENCY (kHz)

100

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

RFB = 1k

CALIBRATION IMPEDANCE = 1k

TA = 25°C

10k

Figure 23. Range 2: Typical % Impedance Error over Frequency

Range 3 (10 kΩ to 100 kΩ)

Output excitation voltage = 2 V p-p

Calibration impedance value, ZCALIBRATION = 10 kΩ

PGA gain = ×1

Supply voltage = 3.3 V

Current-to-voltage amplifier gain resistor = 10 kΩ

0.3

–0.3

FREQUENCY (kHz)

100

0.2

0.1

–0.1

–0.2

RFB = 10k

CALIBRATION IMPEDANCE = 10k

TA = 25°C

50k

100k

Figure 24. Range 3: Typical % Impedance Error over Frequency

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