Ref: Figure 99. Sinc3 Filter Response (10 SPS Output Data Rate, Zero Latency

Disabled or 3.33 SPS Output Data Rate, Zero Latency Enabled)

The filter gain is -120dB for frequencies which are integral multiples of 10. for other frequencies the filter gain varies from -40dB to -100dB. In a practical situation, where the noise can be of any frequency, how does one tackle the problem of lower attenuation?

Hi,

May I know what is your target output data rate and what specific noise frequency do you want to attenuate? Sigma delta ADC are intended for high precision, very low frequency applications. The AD7124-8 uses a digital filter. The digital filter applies only a low pass filter which attenuates high frequency noises but also reduces the frequency bandwidth. As the filter is digital, the frequency response is reflected around the sampling frequency. This means that the filter will provide 0dB of attenuation at frequencies which are integer multiples of the sampling frequency. The most common type of frequency noises in a very low frequency applications are 50/60 Hz noise from AC power lines, and this can also be attenuated by AD7124. For example, by selecting the output data rate to 50SPS or 60SPS, a filter notch is placed on the selected output data rate and multiple of it, thus rejecting the 50Hz or 60Hz noise. However, simultaneous 50Hz and 60Hz rejection can also be achieved by using the REJ60 bit in the filter register. AD7124 also has additional post filter, which also gives simultaneous 50Hz/60Hz rejection with low settling time. We have a Virtual Eval Tool which lets you play with various ADC's performance including the frequency response. You can try and visit this to help you evaluate and understand the ADC performance. If you could also give me additional information regarding your application, it will be great.

Thanks,

Jellenie