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ADS1115 - 16 Bit Aliasing

Kiluba Nicolas
Prodigy 35 points

Other Parts Discussed in Thread: ADS1115

In temperature measurement applications, using the device ADS1115 - 16 Bit in continuous mode, from time to time, aliasing occurs. What can I do to prevent aliasing ? I want to digitize signals between 0 Hz and 1500 Hz. Can anyone suggest me an efficient Anti-Aliasing Filter ?

Regards,

Nicolas

  • 0
    Prodigy 70 points

    ADS1115 can only sample with speed 860 sps so your signal can only has frequency half of that (it's theoretical maximum). If it's higher you will have aliasing. Anti-aliasing filter will make your signal not visible. Because will suppress useful signal, not only noise. You have to find faster ADC.

  • 0 in reply to Lukasz Wozniakowski
    TI__Guru 55466 points

    Hi,

    The ADS1115 is optimized to perform low frequency or DC type measurements such as battery monitoring, or temperature measurement applications.  Most of these applications produce continuous signals that change slowly over time, and tend to be low frequency or could be considered DC signals. These devices include a digital filter that have a frequency response profile similar to a "SINC" function.  These digital filters are optimal for these DC or slow moving signals where a flat frequency response is not required and these digital filters offer a fast settling time.

    As Lukasz mentioned on the post, in order to digitize a signal of a frequency ranging from 0-1500Hz,  the user will need an ADC that offers at least twice the data rate; or aliasing will occur.  For example, if the user has the ADS1115 configured at 860SPS; the signals above 430Hz (1/2 the output data rate), after some attenuation is provided by the digital filter, will alias into the measurement.   When selecting the external anti-aliasing filter, the user will have to consider the external noise or aliasing signals present in the application.   The internal digital filter helps/provides some attenuation and helps reducing the constraints of the analog front-end filter.  In many cases, a simple RC filter with a 3dB corner frequency above the required input frequency bandwidth and a 20dB/decade roll-off combined with the internal digital filter attenuation is sufficient; since most of the signals generated by the sensors are bandwidth self-limited, and the user in many cases is concerned with attenuating higher frequency noise signals that may be present in the application environment.

    Thank you and Best Regards,

    Luis