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Product for high-speed pulse-width measurement

Robert Cachro
Intellectual 845 points

Other Parts Discussed in Thread: TMS320F280025, TMS320F280049, LAUNCHXL-F280049C, C2000WARE

Hi,

Our application requires a real-time pulse width measurement on a digital signal which has a max frequency of 500kHz. This signal's pulse width measurement represents a position value and we need to derive acceleration by computing the double derivative, in real-time, onboard the microcontroller (simple arithmetic). We have successfully tested the validity of this computation by using a DAQ, which has a 100MHz counter timebase, and we were able to accurately calculate acceleration (with some filtering of course). The much higher counter timebase of 100MHz (>> 500kHz base signal) allows us to accurately computer acceleration since derivative calculations require samp_freq >> signal_freq. Now we are planning to calculate the pulse width of the signal using a TI microprocessor which also has a 100 MHz counter timebase and can effectively compute a moving average acceleration value in real-time.

What product would you recommend for this computation? I see the C2000 (TMS32) might fit the bill but I am entirely unfamiliar coming from MSP430/432.

Also, are there any reference examples or application notes that refer to high-speed pulse width measurement?

Thank you for your support,

Robert

  • 0
    TI__Guru* 84390 points

    Robert,

    Thanks for reaching out to us on the E2E.  The module you are looking for on the C2000 MCU is called eCAP(enhanced Capture), and it will be typically clocked at the same frequency as the MCU.  

    In this case you had mentioned 100MHz sampling target, there are two devices I would recommend looking at; either the TMS320F280049 (7 capture modules) or the TMS320F280025 (3 capture modules).  There are several different configurations inside these series of devices, depending on how much memory you need as well as other features.

    You can read more about the capture unit in the F280049 TRM

    In terms of examples and evaluation, I would recommend our LAUNCHXL-F280049C launchpad, is around $30.00 total and will allow you to try out the HW.  The modules on the F280025 are the same, so a code port would be straightforward if you choose that device later on.

    For SW you can find a eCAP example here in C2000Ware or in our cloud version of this here. 

    This should get you started, but please reach back out of you have further questions. 

    We also have a module called HRCAP(High Resolution Capture) on both these devices, which is capable of ~300ps edge placement resolution, but from your description I think eCAP will be adequate.  You'll find that module in the same TRM if that is of interest.

    Best,

    Matthew

  • 0 in reply to MatthewPate
    Intellectual 845 points

    Fantastic, that is exactly the answer I was looking for.

    Section 19.6.3 Example 3 - Time Difference (Delta) Operation Rising Edge Trigger in the F280049 TRM details the exact functionality we are interested in.

    I have ordered a dev kit and will let you know if we have any questions!

    Best,

    Robert