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ADS131E0x need clarification for the noise measurement tables

Oleksiy Pazyuk
Expert 2585 points
Other Parts Discussed in Thread: ADS131E04, ADS131E08

Hi

In the datasheet for the ADS131E04/06/08  there is the table 1 and table 2  where Input noise figures are placed.

But in this tables besides CONGIG1 and Output Data rate is menstioned -3dB bandwidth. Could someone explain what does this  bandwidth mean?

  • 0
    TI__Mastermind 23235 points

    The ADS131E08 is a delta-sigma ADC and  implements a 3rd order low-pass sinc filter as the digital filter used to decimate the modulator output data.

    The -3dB point is the frequency at which the sinc filter of the ADC reaches -3dBFS.  See Sinc Filter Stage section and FIgures 42-45 in the datasheet for more information.

  • 0 in reply to Greg Hupp
    Expert 2585 points

    Hi Greg,

    I understand that for delta-sigma ADC we have internal low pass filter by default. For ADS131E family we have third order low pas filter. Unfortunately it is not clear for me  how could I impact on the Sinc Filterbandwidth .

    Am I correct that bandwidth  of the Sinc Filter is defined only by output rate and we doesn't have any possibility to impact on it?

    I mean next. With DR  BITS 010 I have output data rate 16kSPS with 24-bit resolution. This mean that Sinc filter according to the table 1 or table 2 will be 4192Hz. So this mean that I couldn't measure input signal with frequency 5kHz. This mean that I could only decrease decimation ratio and go to the 16-bit 32kSPS to measure 5kHz signal. Am I right?

  • 0 in reply to Oleksiy Pazyuk
    TI__Mastermind 23235 points

    For the ADS131E0x, you are correct in that you cannot change the behavior of the internal sinc filter.  This is pretty standard behavior for most delta-sigma converters since these filters effect the operation and performance of the device.

    You can still put in signals above the -3dB cutoff frequency (keep below FS/2), however they will be attenuated by the sinc filter as shown in the graphs.  You would potentially want to compensate for the attenuation/droop in the signal magnitude through external/post-processing means.