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How does the ADAU1979 and AD9212 handle signals below 10hz?

I am using the ADAU1979 card to measure vibration using accelerometers and the AD9212 to measure tachometer signals.  I am having some issues with signals below 10hz.  All the individuals who decided on the hardware are no longer with the company.   I am wondering if your card is equipped to handle these signals.  The ADAU1979 has a listed bandwidth of 20hz-20khz in the data sheet.

  • Hi Buzz,

    The ADAU1979 is an ADC that is designed for audio application i.e. 20Hz to 20KHz BW. However the ADC could be used for signals below 10Hz with some limitations. 

    The ADC performance is tested for the 20Hz to 20KHz BW in the DS. so the specifications are valid for this BW only. If using below 10Hz, the noise spec might not be same. 

    The AC input coupling capacitor for the analog inputs might need to be adjusted for the desired BW The input impedance for the ADC is specified in DS and can be used along with the source impedance of the tachometer to calculate the input coupling capacitor value. 

    Is the tachometer output single ended or differential? Depending on the configuration the tachometer output, the ADC input connections will need be set up. I would recommend to use the differential input configuration to reject the common mode noise at the inputs. 

    The full scale output level of your tachometer should match the ADC full scale input to prevent the clipping of signals.

    Regards

    Rajeev

  • Hi, 

    The AD9212 will respond to signals all the way to DC, but the 1/f noise at low frequency would degrade SNR.  High speed converters like the AD9212 are rarely used in this manner, and there is no data on the low frequency degradation.  I would recommend that you look at the low frequency noise while the inputs are floating by doing an FFT in that condition, and verify that the device will provide the performance you need. 

    Regards, 

    David

  • Ok, sorry for my delay.  My real problem is how do I remove this large impulse around 0hz?  Is there a way to do it using the registers?