I am currently using the software example "ImpedanceMeasurement_4WireBioIsolated" and I wanted to check what was the amplitude of the analog excitation signal. Inside the software you can define the peak amplitude of the signal in mV through the variable VPEAK. I have defined a value of 599, which is the default value for this example, and I have connected the oscilloscope to AFE8. I ran the program and the measured amplitude instead of 599mV is more or less 375mV. I tried also other values for VPEAK, but the measured amplitude it's always lower than the desired value, for example I have defined VPEAK at 399mV and measured an amplitude of 255mV. Can someone kindly explain me the reason?
Can you try changing your RTIA value to 1000. I recommend measuring the actual RTIA as well.
#define RTIA (33000) change to --> #define RTIA (1000)
I have made some tests setting directly the DAC value and I have found out that the amplitude of the sinusoid generated by the trasmit stage decrease heavily increasing the output frequency. For example, with a DAC value of 1023, at 15kHz the peak to peak magnitude of the sinusoid generated is about 0.77 V, while with the same DAC value but an output frequency of 50kHz, the peak to peak magnitude of the sinusoid generated is about 0.5 V. Is this something already known? Do you know what could be the reason for this behaviour? Does the excitation stage have some bandwidth limitations in the ADC allowed frequency range (about 80 kHz)?
There is a 3rd order LP RCF filter on receive channel which causes attenuation. This is centered at 50kHz but can have +/-20% tolerance.So the 3rd order roll off could start happening at ~35 kHz.
I did not notice that filter.