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ADS1299: Unipolar/Bipolar Supply for Differential/Single-Ended Inputs

Dennis Ryu38
Prodigy 60 points
Part Number: ADS1299

We are currently using the Differential Inputs mode with no bias or reference electrode, as shown below from the ADS1299 datasheet.

 

We are looking to change to a Single-Ended Inputs mode, as shown below.

 

My question is, does it matter which Power Supply configuration we use for each of the two Analog input modes?

I.e. Does Differential mode need to use Unipolar or Single-Ended need to use Bipolar?

If not, what are the advantages/dis-advantages of using either Unipolar or Bipolar supplies?

Is it Related to the pseudo-differential or fully-differential input signal quality shown below?

  • 0
    TI__Guru 62506 points

    Hello Dennis,

    Welcome to our forum and thank you for your post!

    Either input mode can be used with either supply voltage configuration. Both unipolar and bipolar supply configurations will also give exactly the same performance results.

    What's not shown in Figure 21 and Figure 22 is the absolute voltage relative to the analog supplies. You can assume that VCM is normally close to mid-supply ((AVDD + AVSS) / 2) such that both inputs are allowed to swing equally in both directions. The differential voltage (INxP - INxN) must always be less than abs(VREF) / Gain in order to be converted properly.

    Measuring bio-potential signals with DC-coupled inputs requires you to bias the common-mode voltage of the body. That is the purpose behind the internal BIAS amplifier. Without the BIAS, the VCM of your input signals will be floating and undertmined. They could potential float towards either supply rail and clip the signal.


    Best regards,