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AFE4300 maximum source signal frequency and accuracy

Xavier Fernandez
Prodigy 60 points

Other Parts Discussed in Thread: AFE4300

Hello everyone! We are interested in using the AFE4300 in an electrical bioimpedance measurement (IQ mode). But we want to be sure which is the frequency range of the chip and its accuracy. So, the question is: nowhere in the datasheet it is said what the maximum source signal frequency could be and the accuracy obtainable at this frequency. Using a 1 MHz external clock (as recommended), theoretically, the maximum attainable frequency would be 250 kHz (IQ driven directly by fclk, which should be 4 times the frequency of the DAC output, according to the sheet). Am I right? If so, anyone knows or has tested what is the accuracy measurement in those conditions?

Thank you all!

  • 0
    TI__Mastermind 18305 points

    Yes, you are correct the maximum attainable frequency is 250kHz. However, our maximum source signal frequency is 80kHz. There is a lowpass filter after the DAC with a cutoff frequency of 150kHz +/- 30kHz. So, to keep the signal from attenuating we made the max excitation frequency to be 80kHz.

    After calibration you can get an accuracy of 1%.

  • 0 in reply to Amy Schnoor
    Prodigy 60 points

    Hi Amy!

    Thank you for your reply! I am aware that next to the DAC there is a 2nd order LPF, so, theoretically, the amplitude of the source at 150 kHz would be half of the expected, right? That is 187 uArms approx.  (plus a lag in phase). Yet, would it be possible to carry out measurements at that frequency? I would expect a worse SNR due to the fact that the amplitude of the source would be reduced but I do not know if the IQ demod block would work properly. If it is only a matter of SNR it would not be that bad. In any case, we have just purchased the AFE4300 evaluation board and we will test its performance ourselves. I hope we can post our results as soon as we get them  so that they are useful to anyone with the same doubt!

    Regards