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Phase error when measuring with AFE4300EVM-PDK

Xavier Fernandez
Prodigy 60 points
Other Parts Discussed in Thread: AFE4300EVM-PDK, AFE4300

Hi!

As I said in a previous post, we have purchased the AFE4300EVM-PDK evaluation board and we are using the AFE4300 GUI software to carry out the measurements. The problem is that we are having huge problems when measuring phase in IQ mode. For instance, for a 100 Ohm 1% pure resistor, the measured values for the phase go from 40 to -20 degrees (they greatly vary with the frequency settings). Besides, they also vary with the value of the impedance under test, making impossible any chance of calibration. It seems quite obvious to me that we are committing some aberrant  mistake but, so far, we have not been able to find it out. I attach below a photo of our  hardware setting. Nothing (jumpers, potentiometers, switches) has been modified since we got the board.

Now I shall describe the soft (AFE4300 GUI) settings. 

Global settings: clock 1 MHz (supposed to be internally generated), Internal Vref 1.7 V active, and chip enabled

Weight scale control: disabled

BCM controls: + tension dial to VSENS1 and - to VSENS0. IOUT0 connected to FB0 and IOUT1 to FB1 (at this point, I should ask the upper green connector (J36) contains both IOUT0 and IOUT1 and the lower one VSENS0 and VSENS1, right??). BCM, DAC and IQ are on. (Reference resistors, in case we wanted to use them, are already placed on the board, aren't they??)

ADC controls: BCM AFE I selected for I measurements (BCM AFE Q for Q measurement). ADC is on and 64 SPS.

And these are our settings. Then we measure via the ADC capture & analysis both I and Q components separately.  This way we get both codes for a 100 Ohm 1% resistor. Afterwards, we repeat the same process but replacing the previous resistor with a 220 Ohm 1% pure resistor (rest of the hardware remains the same). This way we obtain the codes of I and Q components for the second resistor. Nevertheless, in spite of using the same frequency for both measurements, we obtain phase values completely different (32º and 6º). In this case, calibration is completely impossible, and what is more, these results suggest a clear mistake either of the hard or the soft settings.

We are now making further investigations to find out what the problem is, but any help would be greatly appreciated.

Thanks in advance!

Best regards

  • Prodigy 115 points

    Good morning,

    I have the same problem. How can I solve it?

    Regards

  • Prodigy 60 points

    Hi!

    I have further information regarding our AFE4300EVM-PDK performance. As you can notice looking at the attached photo, hard settings remain the same as in my previous post except for the connection of the impedance to the AFE4300EVM-PDK: we removed the cables to minimize any parasitic elements and soldered the impedance on a matrix pcb. This 4-wire connection was tested with a commercial impedance analyser and happened to have (with a 18 Ohm 1% pure resistor on it) 18.25 Ohm and 0.2º at 125 kHz. So, this board cannot be the problem.  

     This time we have noticed that, without changing any soft settings (frequency, channel...), phase and quadrature components remain unchanged (to prove this we have acquired 512 samples every 2 minutes, no changes were observed). However, as soon as we changed only the frequency of the current source and changed it back to its original value, the results (both I and Q) were not equal to their previous values at all. That is, results are repeatable as long as no settings are changed and the system is connected to the PC. For this reason, calibration is absolutely impossible. 

    Could anybody throw any light on this? Thank you all!

  • in reply to Giuseppe Giovinazzo
    TI__Mastermind 18275 points

    Giuseppe,

    In IQ mode, switching between BCM DAC frequencies creates this phase error. The phase error will be eliminated in the next rev of the chip.

    For the current version, we have a workaround of calibrating with reference resistor for every impedance measurement. So, do a calibration before every measurement.

  • in reply to Amy Schnoor
    Prodigy 215 points

    Hello,

    i would like to know when the new rev of the chip will be published?

    Thank you.

  • in reply to An Zo
    TI__Mastermind 18275 points

    An,


    There are no concrete dates at this time. I can update you when more information is available.