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ADS1232: EMI problem effects ADC's input signal

Part Number: ADS1232
Other Parts Discussed in Thread: ADS1220

Hi,

The customer has designed their own board with using ADS1232 and a GSM module. they based ADS1232 EVM as reference design. 

they have EMI problem causes from GSM module and the input signal is effected. 

Can you recommend any reference designs including a delta sigma ADC and a GSM module (or a wireless solution instead) 

Thanks,

Mete

  • Hi Mete,

    Board layout is critical in the prevention of RFI into the ADS1232.  Also input filtering is critical.  If ferrites are used then R peaking should be at 1000MHz instead of 100MHz.  I'm not sure that any other ADC will not have the same issues if high gain is being used and high resolution is desired.  The ADS1220 has a TI Design:

    http://www.ti.com/tool/TIDA-00650

    But the resolution will not be as good as the ADS1232.  In the end, proximity analog input signal to the RF source will be an issue.  It is not clear as to what the sensor input is for this design, but if cabling is used from the sensor to the PCB then the cabling will act as an antenna.  So any potential EMI/RFI should be eliminated prior to the ADC, otherwise the noise created will just be passed through or amplified if gain is used.

    Best regards,

    Bob B 

  • Hi Bob,
    Thanks for your reply.
    Do you have any advice on using ferrites? we are not sure which frequency we need to use ferrite on? do we need to use seperate ferrites for Avdd and Dvdd?
    you are right about the cable cabling is used and the problem may cause from cabling.
    Best regards,
    Mete
  • Hi Mete,

    Be careful about using ferrites on supply lines as the inductance of the ferrite can limit (choke) required current demands when powering the device.  It would be better to use a small value of resistance in series with the supply lines to create an RC filter.  You don't want a large voltage drop across the resistor, so I would limit resistance to less than 10 ohms.

    Regarding the ferrites, I was referring to using ferrites at the inputs.  You need to target the ferrites for a large resistance at the frequency range involved to effectively create a larger R for the RC input filter.  There a lot of different approaches that can be used from using a single ferrite to a series of ferrites as well as creating multi-pole filters.  Unfortunately there is no easier answer and requires some experimentation relative to your system.

    A large issue as a part of any system using cabling in an RF environment is noise pickup.  Using a shielded cable with proper termination is the best approach.

    Proper board layout is also essential.  You should create a good ground plane and keep analog and digital signals from crossing paths.  For cable termination you need to keep the shield ground from affecting the analog ground.

    Best regards,

    Bob B