Towards a single-photon energy-sensitive pixel readout chip: pixel level ADCs and digital readout circuitry


San Segundo Bello, D. and Nauta, B. and Visschers, J.A. (2002) Towards a single-photon energy-sensitive pixel readout chip: pixel level ADCs and digital readout circuitry. In: ProRISC 2002, 13th Workshop on Circuits, Systems and Signal Processing, 28-29 November 2002, Veldhoven, the Netherlands.

Abstract:Unlike conventional CMOS imaging, a single
photon imager detects each individual photon impinging on
a detector, accumulating the number of photons during a
certain time window and not the charge generated by the all
the photons hitting the detector during said time window.
The latest developments in the semiconductor industry
are allowing faster and more complex chips to be designed
and manufactured. With these developments in mind we are
working towards the next step in single photon X-ray imaging:
energy sensitive pixel readout chips. The goal is not only
to detect and count individual photons, but also to measure
the charge deposited in the detector by each photon, and
consequently determine its energy. Basically, we are aiming
at a spectrometer-in-a-pixel, or a “color X-ray camera”.
The approach we have followed towards this goal is the
design of small analog-to-digital-converters at the pixel level,
together with a very fast digital readout from the pixels to
the periphery of the chip, where the data will be transmitted
We will present here the design and measurement on prototype
chips of two different 4-bit pixel level ADCs. The
ADCs are optimized for very small area and low power, with
a resolution of 4-bits and a sample rate of 1 Msample/s. The
readout architecture is based around current-mode sense
amplifiers and asynchronous token-passing between the pixels.
This is done in order to achieve event-by-event readout
and, consequently, on-line imaging. We need to read eventby-
event (photon-by-photon), because we cannot have memory
on the pixels due to obvious size constraints. We use
current-mode sense amplifiers because they perform very
well in similar applications as very fast static-RAM readout.
Item Type:Conference or Workshop Item
Electrical Engineering, Mathematics and Computer Science (EEMCS)
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