Analog Devices CN-0217 High Accuracy Impedance Measurements Circuit Note

About this manual

The document presents a reference circuit designed to improve the accuracy of impedance measurements when using the AD5933 or AD5934 impedance converter system solutions. The proposed configuration optimizes the signal chain by buffering the transmit path with a low output impedance amplifier and performing an external current-to-voltage conversion for the receive stage.

The note details specific design considerations, including matching DC bias levels between stages to prevent measurement inaccuracies caused by potential differences. It provides example setups for measuring both low impedance (ohm range) and higher impedance (kΩ range), demonstrating how selecting appropriate calibration resistors and output voltage ranges can minimize errors.

What's inside

• Circuit Function and Benefits
• Output Series Resistance
• Matching DC Bias Levels
• Selecting I-V Buffer Amplifier
• Optimized Signal Chain Configuration
• Low Impedance Range Example
• kΩ Impedance Range Example

Specifications

Frequently asked questions

What is the output impedance for Range 1 excitation?

The output impedance for a 1.98 V p-p output voltage (Range 1) is typically 200 Ω.

Which op amps are suggested for the I-V buffer?

Suggested parts include the AD4528-1, AD8628/AD8629, AD8605, and AD8606.