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ads1278 over sampleing question.

josh wojnas
Intellectual 805 points

Other Parts Discussed in Thread: ADS1278

ads1278 over sampleing question. 

Does the ads1278 set at a data rate for 20k sps does that cover over sampling so the 20k samples per second are over sampled by 2x?

I set the osilator to 16mhz that would allow for 40k sps but my microcontroler is not that fast.

It would be able to handle 20ksps but not 40 so would I be able to pull from the ads1278 at 20ksps and have it have a osilator going at 16mhz to take a max data rate of 40ksps so that the 20ksps that are take out are not bothered by nyquist?

  • 0
    TI__Mastermind 43915 points

    Josh,

    Review the Functional Description of the ADS1278 on page 21 of the data sheet. Table 2 on page 21 breaks down the Oversampling Ratio versus the Mode.

    "In operation, the input signal is sampled by the modulator at a high rate (typically 64x higher than the final output data rate). Since the input signal is sampled at a very high rate, input signal aliasing does not occur until the input signal frequency is at the modulator sampling rate. This architecture greatly relaxes the requirement of external antialiasing filters because of the high modulator sampling rate."

    Table 7 on page 26 can be used to determine the data rate each mode when fclk = 16MHz.

    The setting of the ADC data rate determines the time that you have to read the data out of the ADC before it is updated. So, if your data rate is set to 40kSPS, then you have 25us (1/40,000) to read the data out. I recommend that you select a mode where the data rate is less than 20 kSPS. This way your micro-controller can read the data out in time without any issues.

    Regards,

    Tony Calabria