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MSP430FR50431: Hilbert Option for AbsTOF Acquisition

Part Number: MSP430FR50431

Hello,

Can someone describe how to use the Hilbert option for AbsTOF Acquisition or point me to the documentation?  Specifically, I'm wondering:

1.  How are the coefficients created?

2. How does the trigger threshold algorithm work in this case?  If the envelope of the signal goes up, but then down and crosses the threshold twice, is the first crossing always used?

Thanks!

  • Hi,

    1. We generate the filter coefficients for Hilbert transform for all frequencies, generated in MATLAB.

    For example,

    N = 10;

    hilbertCoeffs = [firpm(N, [0.3 0.7], [1 1], 'h') 0];

    2.You get the max envelope value first. And then search forward to find the first envelope value which below the threshold.

    Best regards,

    Cash Hao

  • Hi Cash,

    Thanks for clarifying.  I will try in Matlab and let you know if I have any questions.

    Can you clarify point 2.  When you say search forward, do you mean the algorithm starts at time=0 and searches the Hilbert transform data forward in time?  Or do you start at the Hilbert transform peak and work backwards in time?  I ask because we sometimes get a little bump at the front of the envelope but the signal goes back down and then up again.  See below:

    We always want to trigger at the earliest threshold cross point in time.  In the example above, we want to trigger at about sample 42, not sample 62 where the threshold is crossed again.  Does that make sense?

    Thanks!

  • HI,

    It starts at the Hilbert transform peak and work backwards in time.

    What is your threshold setting? Sample 42 seems only get 50 ADC codes. Why you need to trigger at a such small threshold? We do not recommend it.

    If you set a proper threshold like 50, the trigger should at around sample 80. It has a strong signal around there, it can hardly get wrong with this setting. And if you need to get the time of the first waveform, you can directly use the time of sample 80 and minus 11 signal period(I count the number in your image) to get it.

    Best regards,

    Cash Hao