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MSP430F6733 sinc3 filter

Other Parts Discussed in Thread: MSP430F6733

Hello

I read something about a sinc3 filter, and there are some information.

But I can't understand its characteristics.

I understand a sinc3 filter is some kind of simple moving average. Is it wrong?

If its ok, I think a sinc3 filter is also some kind of low pass fileter.

That's my understanding.

If you have some information about a sinc3 fileter.

Pleas let me know.

regards

  • >I understand a sinc3 filter is some kind of simple moving average. Is it wrong?

    It is wrong. So called sinc filter usually is FIR filter with sinc impulse response. Sinc function is response of "ideal" low pass filter. This also tells that sinc filter is low pass filter indeed.

    >If you have some information about a sinc3 fileter.

    About DS converters:  part1 and part2.

    Internet have lot of information about sinc filters.

  • Thank you for your reply.

    I understand that a sinc3 filter is like a low pass filter.


    I want more information about a sinc3 filete, that is input step response.
    If you know about input step response, pls let me know.

    MSP430F6733 specification sheet describes about sinc3 filter, and filter characteristics of frequency
    depends on OSR(Over sampling rate).

    If you know about input step response by value of OSR, also pls let me know.


    regards
  • >If you know about input step response by value of OSR, also pls let me know.

    You shall refer to User's Guide of the chip, Digital filter  29.2.7 chapter. There's everything you would want to know to use SD ADC and it's filter.

  • I know about it.

    But it's not what I meant.

    I want to know input step response chart, for example that is below

  • BTW Freq response you show is high pass filter response.

    >I know about it.

    Well, then you shall also read it. What you ask is written there (excerpt):

    Figure 29-7 shows the filter's frequency response for an OSR of 32.

    The first filter notch is always at fS =  fM/OSR.

    The notch's frequency can be adjusted by changing the modulator's frequency, fM, using
    SD24SSELx, SD24PDIVx, and SD24DIVx or by adjusting the oversampling rate using the SD24BOSRx
    registers.

    In case you are not fine with knowing first notch frequency, then you can calculate -3dB cutoff requency using provided formula for filter transfer function which is also there.

  • thank you for your reply.

    then, a sinc3 filter has some cut off frequency which is fS = fM/OSR, right ?
  • >then, a sinc3 filter has some cut off frequency which is fS = fM/OSR, right ?
    No. fM/OSR is frequency of the first notch, not -3dB cutoff. Look at the sinc filter frequency response graph, you will see. I guess that cutoff is around 0.8 * (fM/OSR), but if you want exact number, then you shall calculate yourself. After all formula is there in the Users Guide

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