Unipolar vs. bipolar ECG measurement circuits

Vala

Hi team,

I have a very basic question. Consider that I have three electrodes. In one case I want to make a bipolar measurement (like between electrode 1 and 2, and between electrode 3 and 2). And in another case I want to measure a unipolar signal considering the electrode 2 as reference. How the circuit for these approaches are different? Is there any difference even? I know that in the first case I can connect the electrodes to the inputs of two in-amps. In this case electrode 2 would be connected to both in-amps. Please answer considering two options, with and without Right Leg Drive.

Appreciate any help.

over 10 years ago

0 Amy Schnoor over 10 years ago

TI__Mastermind 18285 points

V3240,

You question is better suited for the Precision Data Converter team who have the ADS129x devices that do ECG. I am moving your post to their forum.

0 Brian Pisani over 10 years ago

TI__Mastermind 38745 points

Hello V3240,

For our devices, there is essentially no difference between measuring differentially between two electrodes and measuring the voltage at one electrode as a unipolar measurement using the other electrode as a reference. In both cases, the measurement you are making is V1 - V2 or V3 - V2. The only difference between using Right Leg Drive and not using Right Leg Drive is that if you do use the RLD, one of your electrodes may not necessarily be measured and will be used exclusively to drive the patient common mode voltage. It's possible to use your RLD electrode as a reference, though its voltage will not move relative to the ADC power supplies and so that is more consistent with your idea of "unipolar" measurement. Hopefully that explanation makes sense.

Regards,
Brian Pisani

0 Vala over 10 years ago in reply to Amy Schnoor

Expert 1110 points

Thanks Amy Schnoor.

0 Vala over 10 years ago in reply to Brian Pisani

Expert 1110 points

Hi Brian Pisani,

Thanks for the good explanation.

Regards

0 Vala over 10 years ago in reply to Brian Pisani

Expert 1110 points

By the way, what do you mean by the TI's devices? Are you referring to AFEs? I want to know more generally actually, mostly in designs using instrumentation amplifier and op-amps. Is there any thing else I should consider using in-amps?

Thanks

0 Brian Pisani over 10 years ago in reply to Vala

TI__Mastermind 38745 points

Hey V324O,

I was referring to TI's delta sigma catalog as opposed to our SAR ADC lineup (or perhaps even non-TI ADCs). Some SAR ADCs measure a single ended signal with respect to the chip ground.

Regards,
Brian Pisani

0 Vala over 10 years ago in reply to Brian Pisani

Expert 1110 points

Thank you so much Brian Pisani.

Regards.

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Unipolar vs. bipolar ECG measurement circuits