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ADS1120: ADS1120 issue

user5195014
Intellectual 450 points
Part Number: ADS1120

Dears

1.ADS1120 Date Rate  up to 1k at normal mode pls check very channel has 1k date rate or four channels total has 1K data rate.

2.what's the sample point ?for example at 1K data rate sample time is 1ms,but in this 1ms time window what's the sample point,the sample result is one time sample or several samples then get average.

3.At DR = 20 SPS why the Date filter could filter 50HZ and 60hz data.

  • 0
    TI__Guru** 112775 points

    Hi user5195014,

    The ADS1120 is an oversampling converter.  The input is actually sampling at the modulator rate which is 256kHz in normal mode (512kHz in turbo mode).  See section 8.3.3 in the ADS1120 datasheet.  The modulator output is processed through an FIR digital filter within the device (section 8.2.4) and decimated to the output data rate.  The design implementation of the FIR digital filter allows for 50 and/or 60 Hz frequency rejection at 20 sps (with the appropriate register settings).  Higher data rates do not have enough data to accurately filter these frequencies with this modulator/filter implementation.

    Aside from the datasheet, you may find the following app notes helpful in understanding the basic operation of the device:

    http://www.ti.com/lit/pdf/slyt423

    http://www.ti.com/lit/pdf/slyt438

    http://www.ti.com/lit/pdf/sbaa230

    The ADS1120 uses a single ADC and an input mux.  At the 1000 sps nominal output data rate, only one input measurement path can be selected at a time, which takes about 1ms for one measurement channel.  However, the actual conversion times are somewhat different than the nominal rates.  The nominal data rates (shown in table 11 on page 28 of the datasheet) is rounded off to simpler numbers. The actual times will depend on the mode of operation (normal or turbo), mode of conversion (single-shot or continuous) and true oscillator operating frequency.  The internal oscillator can vary by as much as +/-2% as shown in the electrical characteristics table on page 7 (Internal Oscillator) and this difference will scale in proportion with the data rate.  For the 1000 sps register setting, the true rate for continuous mode is about 988.4 sps (1/((1/4096000)*4144)) +/- 2% while using the internal oscillator.

    The total time to cycle through 4 channels will also depend on the ability to process the data quickly and change to the next mux input channel.  At the nominal rate of 1000 sps, it would take more than 4ms to cycle through four channels.

    Best regards,

    Bob B