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ADS1281: fIN/fDATA questions

Part Number: ADS1281


 I have some questions to interrupt you about ADS1281.

1) About Figure26&30, what is fIN/fDATA? Does the fIN mean the sinc filter input frequency? While fDATA is the output frequency of sinc filter?

    Are fIN and fFATA the sampling rate? I am not understanding the waveform completely. In addition, what is the Gain of Figure26?

Similar to Figure 29&30, what does the Magnitude mean? 

 2) About Page13, if not used modulator output mode,  DR0/M0 and DR1/M1 float, does it affect  noise function or damage IC? 

Best regards


  • Hi Kailyn,


    1. fIN is the input signal frequency (applied to the ADC inputs). fDATA is the output data data. The ratio fIN/fDATA is a normalized frequency.

      Providing a normalized frequency for the x-axis makes it so that you can reference these graphs no matter which output data rate you select. If we had shown absolute frequency, then we'd need to show separate plots for each output data rate.

      Magnitude (dB) is the "20 * log10( gain )" ratio of the filter's filter's gain/attenuation. Since the FIR filter is a LPF, you'll notice that it significantly attenuates high-frequency signals that are not in the filter's passband region.

    2. Refer to the pin functions table on page 5. If you don't use modulator mode (i.e. you set the MOD/DIN pin LOW), then DRO/M0 and DR1/M1 become digital inputs, which should be pulled HIGH or LOW. If you are in pin mode, these inputs set the output data rate, if not, they are unused, but it is still recommended to tie them low or high through a pull-up or pull-down resistor.

      Generally, if a pin has the potential to become a output signal you should never directly short it to ground or VDD.

  • Hello Christopher,

    Thank  you very much for your detailed explanation.

    Best regards