Hello,
I'm doing measurements with the AFE4300 in I/Q mode on simple parallel networks consisting of a resistor and a capacitor. While the amplitude is measured correctly, the values for the phase seem to have the opposite sign. The absolute value corresponds to the one that I calculated for the network, but I'm expecting negative sign and the AFE gives a positive sign.
I'm sticking to the application report ("Impedance Measurement with the AFE4300"). I also set the frequency only once before measuring the calibration resistors, so I'm following section 8.1.3 "Achieving Deterministic Phase in the IQ Mode " from the data sheet.
To give you an example, these are the values that I measured on a network with a 100 Ohm resistor in parallel to a 4,7 nF capacitor, which should have an amplitude of 99,56 Ohm and a phase of - 5.4°. My calibration resistors in this example are 10 Ohm and 150 Ohm, and I'm subtracting the Phase of the 150 Ohm resistor from the measured phase at R_m.
| raw I value | raw Q value | calculated Phase | calculated amplitude | |
| R_cali_0 | 86 | -17 | ||
| R_cali_1 | 1608 | 1202 | 36.78° | |
| R_m | 978 | 862 | 4.61° | 98.71 Ohm |
So you can see that the absolute value of the phase is pretty close to what you'd expect, but the sign is wrong.
Another issue is that the phase seems to be very off for the 10 Ohm resistor, but that's not my main concern right now.
Do you have an idea why this might happen?
Best regards
Alissa
