Biomedical Engineering Reference
In-Depth Information
Fig. 13.9.
Detector pair rotating around an axis and longitudinally translating
through it
On-column and on-chip approaches are, seemingly, the sole option, along
with off-chip solutions. An example of an off-chip approach was proposed
in [26]. In this design, two technologies are used to independently implement
SPADs and time discriminators that are subsequently connected electrically
using specific techniques.
The development of architectures that support time-correlated modes with
some degree of resource sharing is currently underway in many research
groups. The main trade-off is at the architectural level, due to the nature
of the signal generated by SPDs. In its most general implementation, an SPD
generates a digital pulse when it detects a photon.
Application-specific optimal architectures are possible, provided a model
of the application is built to characterize the performance of the sensor a
priori. The sharing of resources may involve a number of pixels, say 4 or 16,
or on-demand sharing based upon the reaction of SPDs may be used. Other
trade-offs may include the complexity of the time discriminator itself.
13.6 Conclusions
With the introduction of CMOS single-photon avalanche diodes, it is pos-
sible today to achieve great levels of miniaturization. Not only large arrays
of photon counters are now possible, but also very high dynamic range and
timing accuracy have become feasible. Thanks to these advances, applications
requiring time-resolved single photon detection have become possible. Other
applications have reached unprecedented levels of accuracy. We have outlined
some of these applications and we have discussed system issues related to
these and novel applications in the field of bio- and medical imaging.
