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ADS1148 EMC issue

Lorenzo Di Giovanni
Prodigy 100 points


We have to test our device in an anechoic room with EM field in the range 80...2000 MHz with 10 V/m intensity.

Our device measure pressure and temperature by means of a piezoresistive pressure sensor and temperature Pt1000 sensor. This sensors are connected with 1.5 m long shielded cables.

The analog portion of our device is the one attached (1263.1148.pdf)

We found some offset error in the differential reading AIN2-AIN3 when field frequency is about 200 MHz and 400 MHz.

This error has a magnitude of 1-2%. 

Do you have some suggestion to mitigate this phenomenon?

  • 0
    TI__Guru** 113765 points

    Hi Lorenzo,

    It is difficult to say for sure what the mechanism is that is causing the offset.  It could be due to noise aliasing back through the ADC, or it could be due to the noise creating a differential voltage across the caps C27 and C58.  Even though you don't have a specifically designed RC filter, there is some resistance in the leads.  If the noise is being filtered slightly differently between the inputs, then you may see an offset created by this differential voltage.  This affect appears worse when any gain is applied to the input signal as well.

    I'm not sure if you are using a shielded cable from your pressure sensor.  A shielded cable that is properly terminated should help with any common mode RF noise that is picked up.  You could also create a RC filter (which is a good idea for anti-aliasing) by adding series resistor and a capacitor across the differential input pair.  The differential cap must be 10 times larger than the common mode caps (the ones from the input to ground) or you may see the same effects returning. Adding a ferrite in series with the input lines may also help. 

    Best regards,

    Bob B