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Testing ADS1298ECG-FE user development kit with function generator

Komal Mariam
Prodigy 130 points
Other Parts Discussed in Thread: ADS1298

Hi all,

I am testing ADS1298ECG-FE with function generator. The User's guide document says in Section 5.7.2:

"The input signal must be connected differentially since each ADC channel input is differential. If it is desired to connect single-ended signals, bias the negative input of the channels to a mid-supply voltage."

Can anyone please explain what do they mean by 'connected differentially' and 'bias the negative input of the channels to a mid-supply voltage'

Thank you in advance

Komal

  • 0
    TI__Mastermind 38745 points
    Hi Komal,

    This statement is essentially telling users to make sure that the input from the function generator has a common mode range such that the individual input signals do not exceed their valid range for the device with respect to the supplies. The device just measures AINP-AINN, so if you were interested in measuring a signal from a function generator, you'd have to feed that signal to the positive input, ensuring its level with respect to the chip supplies was valid, then feed a DC voltage to the negative input, ideally the mid-supply voltage. The output from the ADC will be your signal with respect to the DC voltage you input on the negative input terminal - a differential measurement .

    For the ADS1298, the mid-supply voltage is available to you as an output from the RLD amplifier. The purpose of the RLD amplifier in an application system is to bias the body to mid-supply, but you can use it in this case to provide a mid-supply voltage to the negative input terminal by fly-wiring it in. Hopefully that answer made sense. Let me know if I need to clarify anything.

    Regards,
    Brian Pisani