Hi All,

I have a AD5933 impedance measurement question, when I measured frequency 1k-100kHz for only resistor, and calculated the impedance by the formula which datasheet provided, I got decreased impedance with increase frequency.

My circuit only have AD5933 chip with 1uF and 10uF capacitor connect between VDD and GND.

I used 51kohm resistor for feedback resistor and calibrated by 200kohm resistor, which I followed this article(https://www.analog.com/media/en/technical-documentation/application-notes/AN-1252.pdf) to calculate my feedback resistor and calibration resistor. My VDD = 3.3V, Gain = x1, Frequency increment = 1kHz, clock = internal clock(16M). The resistor range I want to test is 100kohm to 510kohm.

First picture tested on the calibration resistor, and this seems okay.

Second picture tested on 100kohm resistor.

Third tested on 330kohm resistor.

Last tested on 510kohm resistor.

And I had find someone said the testing range of different calibration resistor and feedback resistor, like if I want to test 100k-1Mohm resistor, I need to use 100kohm resistor for calibrating and 100kohm resistor for feedback, but the result looked similar like above.

Thank if anyone help me!!!!