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CCS/ADS1147: ADS1147 filtering function?

Yang micco
Prodigy 30 points
Part Number: ADS1147
Other Parts Discussed in Thread: ADS1260, ADS124S06, ADS1120, ADS114S06, ADS1220, ADS1235

Tool/software: Code Composer Studio

Hi：

I used ADS1147 to capture the instantaneous maximum signal, but the test is currently wrong. Does the ADS1147 have a filtering function that will not capture the largest signal?

  • 0
    TI__Guru** 113765 points

    Hi Micco,

    Welcome to the E2E forum!  The ADS1147 is an oversampling ADC that samples at the modulator rate and then uses an FIR filter to output the data at the selected data rate chosen in the register settings.  The modulator rate changes depending on the chosen data rate and is shown in Table 5 on page 22 of the ADS1147 datasheet.

    The Digital Filter is also discussed on page 22 of the datasheet with the filter specifications shown in Table 6.  Most likely the signal you are attempting to capture is being lost due the digital low-pass filter.  If you need capture a fast transient, then most likely you will need to use a different type of ADC such as a SAR type converter.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 30 points

    Hi Bob：

    1. Is there a corresponding register that can be modified? (for ADS1147)


    2. Since my front end is connected to a load cell, are there any relevant models to push? (must to fast capture data)

         the devices need a low-noise, PGA, a precision delta-sigma (ΔΣ) ADC 

  • 0 in reply to Yang micco
    TI__Guru** 113765 points

    Hi Micco,

    For the ADS1147, the data rate can be changed in System Control Register 0 in bits 3:0 with the maximum data rate at 2000 sps.  This means that by Nyquist theorem the fastest measurable frequency is 1000 Hz.  However, due to the response characteristics of the filter there may be some degradation at 1000 Hz.  See Table 6 and Figure 35 of the datasheet.

    I would suggest not using the ADS1147 for load cell measurements.  To achieve the lowest noise and lowest drift of the measurement the measurement itself should be made ratiometric.  This means that the excitation source of the load cell should be the same as the reference.  The ADS1147 is limited in the reference voltage that can be applied and can no be no greater than (AVDD-AVSS) -1V.  This limitation will reduce the signal-to-noise of the load cell output.  Second thing to consider is the faster the measurement the noisier the conversion result.  So low-noise and fast data rates don't correlate well with each other.  Third thing to consider is the actual measurement resolution desired from the load cell.  The output of the load cell is only a small portion of the full-scale range of the ADC, so don't expect to get 16-bits of measurement range of the load cell.

    Devices that would be better alternatives are ADS1220 (ADS1120), ADS124S06 (ADS114S06), ADS1235, and ADS1260.  There are bridge circuit examples in these device's datasheet.

    Best regards,

    Bob B