Effective noise bandwisth of AD7175-8 and AD7176-2

Hello,

I have a question from a customer about effective noise bandwidth of AD7175-8 and AD7176-2.

In the datasheet for LTC2444, EFFECTIVE NOISE BW is presented in table-8.

The customer need to know the same parameter to estimete SNR of his system.

Could you please present the effective noise band width of AD7175-8 and AD7176-2 ?

Best regards,

ysuzuki

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  • Hi,

    Apologies. But this is not possible for AD7175. You cannot bypass the sinc filter but the AD7175 offers a number of different filter settings selectable by the user. A sinc filter is used on these precision low bandwidth sigma delta ADCs as it has low latency or low settling time. A sinc type filter always provides this type of profile i.e. deep notches at the programmed output data rate with less attenuation at other frequencies. Target ODR will determine the required decimation rate. The minimum oversampling ratio of the AD7175 is ×32, so given the 8 MHz FMOD, the maximum output data rate offered is 250 kHz. Filter choice affects the filtering of quantization noise thus a higher order filter is more than sufficient to eliminate the modulator noise. Beyond filtering quantization noise, the digital filter can be used to trade off input bandwidth for lower noise. This is done by increasing the decimation rate. So what I was saying is the ADC filter and decimation rate is configurable via registers based on your target application and noise performance. You can see the filter response of the AD7175/AD7176 on EVAL+ Software and Virtual Eval Tool. The datasheet also show noise numbers at different ODR and filter settings.

    Thanks,

    Jellenie

     

Reply
  • Hi,

    Apologies. But this is not possible for AD7175. You cannot bypass the sinc filter but the AD7175 offers a number of different filter settings selectable by the user. A sinc filter is used on these precision low bandwidth sigma delta ADCs as it has low latency or low settling time. A sinc type filter always provides this type of profile i.e. deep notches at the programmed output data rate with less attenuation at other frequencies. Target ODR will determine the required decimation rate. The minimum oversampling ratio of the AD7175 is ×32, so given the 8 MHz FMOD, the maximum output data rate offered is 250 kHz. Filter choice affects the filtering of quantization noise thus a higher order filter is more than sufficient to eliminate the modulator noise. Beyond filtering quantization noise, the digital filter can be used to trade off input bandwidth for lower noise. This is done by increasing the decimation rate. So what I was saying is the ADC filter and decimation rate is configurable via registers based on your target application and noise performance. You can see the filter response of the AD7175/AD7176 on EVAL+ Software and Virtual Eval Tool. The datasheet also show noise numbers at different ODR and filter settings.

    Thanks,

    Jellenie

     

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