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Delta Sigma Modulator SDFM LaunchPad TMS320F28377S

Andreas Mueller90
Prodigy 30 points
Other Parts Discussed in Thread: TMS320F28377S, AMC1304M05

Hi Folks,

This is my first post to E2E. I found it very helpful to learn things quickly and I appreciate this effort from TI.

I am a beginner in Microcontrollers and I am using Delfino LaunchPad in my master internship. I have a querry from SDFM module of TMS320F28377S.

a) Why the Data Rate of Sigma Delta Modulator (ADC) depends on the input control unit of digital filter (SDFM) ? I mean, if I am operating in Mode_0 and my modulator clock is 20MHz, my modulator data rate will also be 20MHz?

If I use sinc3 filter with maximum OSR 256 at a clock frequency of 20Mhz, I get filter Data Rate of 78KSPS but my filter Latency is three times more than time period of my sinc3 filter ( which should be 1 / Filter Data rate = 1/ 78KSPS = 12.9 micro-seconds) i-e 38.7 micro-seconds

b) So my confusion is, if the output of filter could be seen on oscilloscope for example or in software, what would be sinc3 filter waveform frequency? 1/ Latency or 78 KSPS? Because their reciprocals aren't equal.


I would be thankful if someone can clear my confusion.

Best Regards,

Andreas

  • 0
    TI__Guru 55700 points
    Andreas,

    Data rate of SD-modulator and data rate of SDFM are different.

    Data rate of SD-modulator is the sampling rate of the SD-modulator. Whereas, data rate of SDFM depends on sampling rate of modulator and OSR configuration.

    Sinc filter waveform should be the digital representation of analog signal fed to SD-modulator. In your example, Sinc3 filter would produce a new data at 78 KSPS (or every 12.8 us).

    Regards,
    Manoj
  • 0 in reply to Manoj Santha Mohan
    Prodigy 30 points
    Hi Manhoj,

    Thank you for your reply.

    a) So the data rate of Delta Sigma Modulator (e.g AMC1304M05) will be equal to the clock frequency provided at CLK input?
    Data Rate of filter can then be obtaind by : Data Rate of Modulator / OSR

    b) Sinc3 filter would produce a new data every 12.8 us for 20MHz CLK and OSR_256, latency is something else? I was thinking latency is the time at which the filter is updating its output. (Latency is 3*times update rate of filter : 38,46us)

    Looking forward to your reply.

    Andreas
  • 0 in reply to Andreas Mueller90
    TI__Guru 55700 points

    Andreas,

    a) For AMC1304, data rate is equal to clock frequency provided at CLK input. But, there are modulator is market whose data rate is half the clock provided in CLK input.


    b) Yes, that's correct. Please refer TRM to understand the differences between latency and data rate.


    Regards,

    Manoj

  • 0 in reply to Manoj Santha Mohan
    Prodigy 30 points
    Thankls alot Manhoj.

    It killed my confusion.

    Andreas