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ADS1298: Test input signals have different offsets as compared to dev kit

Part Number: ADS1298
Other Parts Discussed in Thread: , TEST,

Hi there,

Background

We did some tests recently to compare our custom design (using ADS1298) against the development kit (ADS1298RECGFE-PDK - note the 'R'). We conducted 2 different tests to compare the signals:

  1. Test input signal
  2. Using a simulator to simulate a square wave

Our observations are that:

  1. We are seeing that the amplitudes are the same; but
  2. The offset of the signals are different


Test results
I have attached some images for reference:-

Test input signal comparison


Square Wave signal comparison



Questions

  1. Is this expected?
  2. Are the test input signals different for ADS1298 and ADS1298R?
  3. And if not, any thoughts on why this is the case?


Request for suggestions for troubleshooting steps (if any)
If this is unexpected, could you offer some other troubleshooting steps please?

Thank you in advance.

Best regards,
Eric

  • Hi Eric,

    It is normal for the device offset to vary from device to device and channel to channel (+/-500uV for gain =6). You can verify this by setting the device channel input to Input-Shorted and comparing the offset from the test signal output. There is no difference between the test signal for the ADS1298 and ADS1298R.

    Thanks

    -TC

  • Hi TC,

    Thanks for that.

    We did that comparison, and while the amplitudes are the same, the offsets are different.

    Custom Design (ADS1298)

    Dev Kit (ADS1298RECGFE-PDK)

     

    Offset (mV) Offset (mV)
    CH1 -0.07 -0.6
    CH2 -0.14 +0.27
    CH3 -0.24 -0.23
    CH4 +0.06 -0.4
    CH5 -0.1 -0.4
    CH6 -0.09 -0.25
    CH7 +0.02 -0.28
    CH8 +0.02 -0.28

    Although the differences between offsets are within +/-500uV, we are keen to understand differences in results for Input-Shorted test signal are meant to be different. Could you let us know please?

    Thanks,

    Eric

  • Hi Eric,

    The device contains eight individual programmable gain amplifiers and ADC for each channel. Hence, the offset will differ for each channel due to design matching and manufacturing variation.

    Thanks

    -TC