AFE4400 Ambient noise cancel

Takumi Suzuki1

Mastermind 8610 points

Hi,

I would like to ask you a question about "ambient noise calcel" as below.

There is a following equation on datasheet p26.

Here, we can control "I cancel" value is from 0 - 10uA, step 1uA.

For example, in case of Rg=100K and Icancel =1uA, output value of "cancel" part is 0.2V.

(2*Icancel*Rg = 2*1uA*100K = 0.2V)

On the other hand, the full-scale of the ADC is +/-1.2V.

I suppose the cancel voltage of 0.2V seems to be too rough against ADC range. (0.2V vs 2.4V)

I am afraid this is not very useful for SpO2 product.

Will you tell me how to improve the resolution of "I cancel" if you know?

Or if my understanding is not correct, please let me know.

Thank you for your support.

over 9 years ago

0 Praveen Aroul over 9 years ago

TI__Mastermind 49946 points

Hello Takumi,

The ambient cancellation DAC is enabled during high ambient light condition, in conjunction with the second stage gain to maximize the ADC dynamic range. You are correct in your understanding. The minimum cancellation voltage (output referred) is 0.2V. But the benefit of ambient cancellation DAC is realized for very high ambient currents. With smaller ambient current levels, by using the digital subtraction (LED - AMBIENT), the additive effect of the ambient light in the LED phase can be cancelled out.

0 Takumi Suzuki1 over 9 years ago in reply to Praveen Aroul

Mastermind 8610 points

Hi Praveen-san,

Thank you for your answer!
I understood.

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AFE4400 Ambient noise cancel