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

  • Hi,

    Apologies, this was missed. May I know what is your application and why do you need this type of information? The AD717x is designed for dc type of application. May I know what input frequency will you intend to operate or what sensor are you going to use? Since the digital filter filters out the wideband noise from the input signal, I think the wideband noise is not much of the concern if you intend to operate at very low frequency. If you take a look at the example on the LT part, from the total noise, the wideband noise is much smaller than the ADC noise so the ADC noise dominate the total noise. But if you would like to see the filter response of the AD7175/AD7176 we have EVAL+ Software and 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. 

    Thanks,

    Jellenie

  • Hello Jellenie,

    Thank you for your support.

    This application is about cardiography and the noise level requirement is too small.

    > The AD717x is designed for dc type of application. 

    From the ideal of this customer, he thinks the best way is to bypass the sinc filters.
    If it is able to , the customer will make and tune the original decimation filter on FPGA.

    Is AD7175-8 able to baypass the sinc filter ?

    Best regards,

    ysuzuki

  • 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

     

  • Hello Jellenie,

    Thank you for your suggestion and advice.

    I feel a combination of "minimum oversampling ratio" configuration and custom decimation filter will be better solution.

    I would like to inform this idea to our customer.

    Thnak you,

    ysuzuki