Adaptive high speed low noise detector electronics are being developed for a UV imaging instrument for application to
astronomy and planetary science space missions and for various other terrestrial high speed imaging applications.
Forthcoming space missions such as ESA JUICE1 and the World Space Observatory2 have requirements for UV photon
counting imaging detectors with high dynamic range, high spatial resolution and high radiation tolerance. Imaging
techniques that can adapt to different luminosity conditions and optimise the image spatial resolution against the
incoming photon event rate can provide significant performance advantages.
We introduce an imaging photon counting Microchannel Plate (MCP) detector utilising a low noise Capacitive Division
Image Readout (C-DIR)3 with adaptive pulse shaping capability. Our experimental setup provides controllable photon
count rates for end-to-end detector performance measurement and system calibration. It uses a four channel fast digitiser
which enables us to easily investigate various digital pulse shaping techniques and vary shaping time constants to assess
their impact on detector performance.
In this paper we describe our laboratory experimental setup, illustrate the method of imaging from photon counting and
describe techniques for quantifying the image spatial resolution. Finally we present our current set of results comparing
the measured spatial resolution with the theoretical determined from the measured intrinsic electronic noise of the
The Capacitive Division Image Readout (C-DIR) is a simple and novel image readout for photon counting detectors
offering major performance advantages. C-DIR is a charge centroiding device comprising three elements; (i) a resistive
anode providing event charge localization, event current return path and electrical isolation from detector high voltage,
(ii) a dielectric substrate which capacitively couples the event transient signal to the third element, (iii) the readout
device; an array of capacitively coupled electrodes which divides the signal among the readout charge measurement
The resistive anode and dielectric substrate constitute the rear interface of the detector and capacitively couple the signal
to the external C-DIR readout device. The C-DIR device is a passive, multilayer printed circuit board type device
comprising a matrix of isolated electrodes whose geometries define the capacitive network. C-DIR is manufactured using
conventional PCB geometries and is straightforward and economical to construct.
C-DIR’s robustness and simplicity belie its performance advantages. Its capacitive nature avoids partition noise, the
Poisson noise associated with collection of discrete charges. The dominant noise limiting position resolution is electronic
noise. However C-DIR also presents a low input capacitance to the readout electronics, minimising this noise component
thus maximising spatial resolution. Optimisation of the C-DIR pattern-edge geometry can provide ~90% linear dynamic
We present data showing image resolution and linearity of the C-DIR device in a microchannel plate detector and
describe various electronic charge measurement scheme designed to exploit the full performance potential of the C-DIR