Photodiode amplifier

[jctoday]

Hi all,

I recently ran across a switched capacitor integrating transimpedance amplifier for photodiode app note from TI for IVC102 device. In a more conventional design, one would use one amp for one photodiode to integrate the charge from the photodiode. But in this article/schematic, they showed a circuit with one photodiode using two IVC102's in differential mode claiming that it cancels out photodiodes' dark current and ambient light.

Could someone please explain as to how this circuit works to detect light of interest but can canceled out unwanted light in this differential mode? Does it work with AC signal only?

Thanks!

 

[alec_t]

Can you post a link to this circuit? Like photodiodes, we can't work in the dark!

 

[crutschow]

In general a differential circuit cancels any signal that is common to both inputs (it generates no output signal). If the two diodes are looking at the same scene they will both be generating the same dark current and ambient light current, so they are both canceled. Any signal applied to only one input, however, would be amplified and appear at the amplifier output). For this cancellation to work properly the signal of interest must be applied to only one input.

 

[jctoday]

Oops, the attachment wasn't uploaded completely before I submitted the message. The picture is from TI's Medical Solution Guide under Pulse Oximeter section.

https://www.electro-tech-online.com/custompdfs/2011/08/slyb108e.pdf

Thanks!