Thursday, March 17, 2011

SPAD Imagers Overview

Edoardo Charbon published a popular overview of SPAD imagers, the approaches to single-photon imaging and bibliography. The overview is titled "CMOS integration enables massively parallel single-photon detection" and can be found on SPIE site.


  1. is there any commercial product based on SAPD?

  2. There is some interesting SPAD reading if you search for "SPAD" and "imager" at Google.

    It looks like one of the main applications will be identifying unknown molecules by tagging them with a fluorescent dye, then wiping them on an array of known receptor molecules on a substrate, then illuminating them, then counting emitted photons from each test site to see if a tagged unknown molecule attached there. Apparently it is important to determine not just how many photons are emitted, but when, in order to best identify the attachment site. The arrival profile is basically a signature, and you want to be able to distinguish between similar signatures if you can.

    The SPAD pixel sizes are really large and the array resolutions are really small compared to, say, a CIS for a mobile phone, but the known molecule array sizes are also really small in comparison. The advantage of a SPAD imager in this application is probably something like being able to test against 1000 known molecules in parallel rather than against 100 in parallel in each of 10 tries. So faster testing, or testing against more candidate receptor molecules, or better test accuracy might be possible.

    I suppose "it looks like there's potential" is a bit of an ambivalent answer to the question, but it's the only one I have at the moment.

  3. @ "is there any commercial product based on SAPD?"

    sensL offers few products:

  4. What is the fundamental difference between APD and SPAD??

    1. SPADs operate in Geiger mode in which the Photodiode is biased witha voltage bigger than (More Negative) the breakdown voltage. Therefore, the diode is in a state that dven a single photon imoinging on it can trigger the avalanche. So they are used for single photon detection and have a lot of sensitivity and speed.

  5. A Spad is operated in Geiger mode and may have additional detailed design in the guard ring area to accomodate this mode of operation.


All comments are moderated to avoid spam and personal attacks.