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Using the AD5933 Evaluation Board for Low Frequency Measurements

Question asked by AWilhelm on Jul 3, 2017
Latest reply on Jan 29, 2018 by ronishi3



I have been trying to perform low frequency (less than 10 kHz) impedance measurements using the AD5933 Evaluation Board (EVAL-AD5933EBZ). My understanding is that to perform measurements at frequencies less than 10 kHz, I simply need to reduce the system clock. To achieve this, I removed Link 3, connected Link 4, and then connected a function generator via the CLK 1 input. I then used a square wave with an amplitude of 3.3 volts to replicate the clock signal.


I then proceeded to perform low frequency measurements. First I adjusted the function generator to have a frequency of 8 MHz and updated the external clock value in the program accordingly. I then performed frequency sweeps. For measuring real impedance, the board returned correct results. However, for complex impedance (i.e. a capacitor), the results were inaccurate. I then proceeded to do more tests with the evaluation board, lowering the external clock signal. At around 100 kHz, the board started to become unresponsive. I could usually program the device registers, but sometimes calculating the gain factor would cause the device to hang and not return a calculated gain factor value.


Is my understanding of how to perform low frequency measurements correct? Furthermore, when lowering the frequency of the master clock for the AD5933, does this affect I2C communication (i.e. is that why the board starts to become unresponsive)? If so, is there a way to correct this?