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Sigma-Delta ADC low frequency attenuation

viliamklein
on Apr 9, 2016


I have a simple question about sigma-delta converters. I've noticed a lot of the products seem to have filters designed attenuate low frequencies. For example, the AD7781 datasheet shows -50dB gain for a 10Hz signal (see image). For my application, I would like to measure some low frequencies out of a pressure sensor. Should I really expect to see -50dB attenuation if my source is a 10Hz wave?

Thanks for your help!

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    •  Analog Employees 
    on Apr 10, 2016 7:32 PM

    Hi, VilliamKlein.

    For AD7781, the filter response for output data rate of 16.7Hz shows a -50dB attenuation, but this notch is for frequency around 8.5Hz. For 10Hz, you will be expecting around -13dB attenuation. Sigma delta ADC are intended for high precision, very low frequency applications. Thus, the digital filter applies only a low pass filter which attenuates high frequency noises but also reduces the frequency bandwidth.

    Thanks,

    Jellenie

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    •  Analog Employees 
    on Apr 10, 2016 7:32 PM

    Hi, VilliamKlein.

    For AD7781, the filter response for output data rate of 16.7Hz shows a -50dB attenuation, but this notch is for frequency around 8.5Hz. For 10Hz, you will be expecting around -13dB attenuation. Sigma delta ADC are intended for high precision, very low frequency applications. Thus, the digital filter applies only a low pass filter which attenuates high frequency noises but also reduces the frequency bandwidth.

    Thanks,

    Jellenie

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