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Configuring ADS1298R ADC

Purushottam BE
Prodigy 130 points
Other Parts Discussed in Thread: ADS1298

I have two questions.

1) I believe the Sigma delta ADC can be configured for either unipolar or bipolar. Could someone tell me how to configure that. If it is unipolar how does it measure PQRST ECG signal (Negative part of the ECG wave) ?

2) Also about the ADC (digital count format).

    I mean if IN1P is fed with 1mV DC and IN1N = 0V, and VREFP is at 2.4V , VREFN @ 0V. How much will ADC count?

For the same input of 1mV, how    much will be the ADC counts when configured in bipolar mode?

  • 0
    TI__Guru 57326 points

    Hello Purushotam,

    Unipolar and bipolar modes are simply referring to the analog power supplies on the ADC. This only dictates the maximum voltages that can appear on the input pins. The differential signal (INP - INN), however, is compared to the reference voltage (VREF = VREFP - VREFN) and can be anywhere between -VREF and +VREF, so it is not a problem for INP - INN to be a negative result. Please refer to the Data Format section on Page 46.

    If you wish to hold INN at 0 V, you will need to operate the ADS1298 with bipolar supplies (i.e. +/- 2.5 V). This will allow the positive input, INP, to swing above and below the 0 V common-mode input voltage. As long as the absolute value of your differential input voltage is less than VREF, you are good to go.

    To determine the number of ADC counts, you need to calculate the least-significant bit voltage (LSB) = [ 2*VREF ] / [(2^24) - 1]. Again, refer to the Data Format section to see how we use 2's compliment to convert positive and negative differential inputs into output codes.

    Best Regards,