A new family of pixel detectors for high frame rate X-ray applications Roberto Dinapoli à , Anna Bergamaschi, Beat Henrich, Roland Horisberger, Ian Johnson, Philipp Kraft, Aldo Mozzanica, Bernd Schmitt, Xintian Shi, Dominic Suter Paul Scherrer Institut, 5232 Villigen PSI, Switzerland article info Available online 24 October 2009 Keywords: Synchrotron radiation instrumentation Photon counting Pixel detectors CMOS electronics abstract We are developing a new family of hybrid, single photon counting X-ray detectors for very high frame rate applications. A dedicated readout chip was designed, to be used as building block for detectors up to 9 Mpixel and about 550 cm 2 area. It has an area of 19:3  20:0 mm 2 and contains 256  256 pixels of 75  75 mm 2 , resulting in an active region of 19:2  19:2 mm 2 . Each pixel contains a 12 bit counter with double buffering for continuous image acquisition. Moreover, it allows a partial readout (4, 8 or 12 bits) with corresponding frame rates up to 24, 12 and 8 kHz. The chip is designed with Hardening By Design techniques [1], to obtain high radiation tolerance from a standard commercial 0:25 mm CMOS technology. The chip was recently received from fabrication and it is at present under test. & 2009 Elsevier B.V. All rights reserved. 1. Introduction The success achieved by the PSI-SLS detector group with the development of the Pilatus [2] and Mythen [3] detectors pushed the research for a much more advanced family of pixel detectors, addressing several needs which were highlighted by our users community. In particular, smaller pixels and faster frame rate (possibly with negligible dead time) were considered as crucial specifications. 2. Readout chip main features In fact, the new readout chip keeps the noise and speed performance of the previous chip of the Pilatus family (Pilatus II) and improves it in every other respect. Table 1 summarizes the features of the new readout chip and of its pixel. To be noticed are in particular pixel size (reduced 45x with respect to Pilatus II), pixel count ( 411x), double buffering (not present in Pilatus II), but most of all readout speed ( 41000x for big detectors, see also Section 5). 3. Pixel architecture Fig. 1 shows a schematic representation of the pixel architecture. The charge signal from the sensor is amplified and filtered by the low noise preamplifier and following shaper with tunable shaping time. The shaped signal is fed to a comparator with a reference voltage that is given by a global threshold and the on-pixel trim DAC (6 bit). An incoming signal exceeding this threshold will toggle the comparator state. If the chip is in Expose mode (Enable high) and the pixel did not overflow, the comparator pulse increments the digital counter by one. At the end of the exposure time the counter content is stored temporarily in a pixel buffer, and the counter is reset to allow immediately a new exposure. ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/nima Nuclear Instruments and Methods in Physics Research A Table 1 Summary of the main features of the readout chip and of its pixel. Readout chip features Technology UMC 0:25 mm Power supplies 1.1 V (ana.), 2 V (dig.), 1.8 V (I/O) Rad. tolerance Rad-tolerant design ( 44 Mrad) Pixel array 256  256 ¼ 65 536 Chip size 19:3  20 mm 2 Readout speed up to 24 kframes/s Pixel features Pixel size 75  75 mm 2 Gain 44:6 mV=e  Peaking time 31 ns Ret. to 0 at 1% 151 ns Noise (simul.) 135 e  rms Static power 8:8 mW=pixel Transistor count 430/pixel Pixel counter Configurable (4, 8, 12 bit mode), binary, double buffered for continuous readout Threshold adjust 6 bit DAC/pixel Other features Overflow control, single pixel addressing and analog out for testing Simulations are done with ‘‘standard’’ settings. ‘‘Low noise’’ or ‘‘high speed’’ settings can improve performance for applications with specific needs. 0168-9002/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2009.10.043 à Corresponding author. E-mail address: roberto.dinapoli@psi.ch (R. Dinapoli). Nuclear Instruments and Methods in Physics Research A 617 (2010) 384–386