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Offset calibration in ADS1148

Hak-Jin Jeong
Intellectual 350 points
Other Parts Discussed in Thread: ADS1148, ADS1248

I have one question about gain/offset calibration (whatever it is system or self).

ADS1148 has eight channels, but, there is only one 24 bit OFC and FSC Register.

It means that these offset anf full scale calibraion is common for all channelsl (not separately)?

Is it true?

In my opinion, there might be difference between input filters of each channel.

How can we deal this difference?

I am a little bit confused.

Thank you for your help in advance.

Best Regards

Hak-Jin Jeong

  • 0
    TI__Guru* 97585 points
    Hak-Jin,


    It is true, that there is only one OFC and one FSC register. These registers are designed to remove the offset and the gain from the ADC itself. As an example, the OFC might remove the offset from the front end PGA, while the FSC may remove the gain error from the PGA and the sampling capacitors in the ADC.

    Note that there is only one PGA and ADC in the device. The channel switching is done by the multiplexer. In most cases, the OFC and FSC values hold from channel to channel. However, you might need to adjust the FSC if you change the PGA gain for each channel.

    If you believe that you need better calibration values for each channel, you could test the device in the system and record the FSC values for each channel after a calibration. Again, you may want to do this if you change PGA gain. Another option would be to use the ADS1248 instead of the ADS1148. For the ADS1248, the ADC automatically updates the FSC with a factory programmed value. This reduces the ADS1248 gain error to ±0.02%, from the ADS1148 gain error of ±0.5%.


    Joseph Wu