Novel pixel-circuits allowing implementation of Video-Rate MegaPixel Fluorescence-Lifetime Image Sensors

Fluorescence lifetime of molecules can be considered as an
additional color, revealing crucial invisible information in a large
range of applications, spanning from microscopy of biological cells to
image guided surgery. Users are longing for cameras that can image
this fluorescence lifetime at a high resolution and at video-rate
speed. The detector of choice to achieve this is the Single-Photon
Avalanche Diode (SPAD) because it can deliver directly a digital
output that includes the precious time-of-arrival (ToA) of each
received photon. Current state-of-the-art systems communicate these
received ToAs from the sensor to an external processor for
computing the lifetime estimation. However, more than thousands of
ToAs/pixel/frame are required for good accuracy and precision. For
mega-pixel-resolution at video-rate operation, data congestion forms
however an imminent showstopper.
In the project we will use an elegant in-pixel, partly analog circuit, to
provide for a lifetime estimation method that only occupies a small
silicon area, supports good fill-factor, low power operation, and that
has a large dynamic range for the incoming fluorescence light. The
uncalibrated sensor output is targeted to deliver direct information
with better than 3% precision for lifetimes down to ~300ps, being
sufficient for most foreseeable applications.