title: Centroiding algorithms for high speed crossed strip readout of microchannel plate detectors.
abstract: Imaging microchannel plate (MCP) detectors with cross strip (XS) readout anodes require centroiding algorithms to determine the location of the amplified charge cloud from the incident radiation, be it photon or particle. We have developed a massively parallel XS readout electronic system that employs an amplifier and ADC for each strip and uses this digital data to calculate the centroid of each event in real time using a field programmable gate array (FPGA). Doing the calculations in real time in the front end electronics using an FPGA enables a much higher input event rate, nearly two orders of magnitude faster, by avoiding the bandwidth limitations of the raw data transfer to a computer. We report on our detailed efforts to optimize the algorithms used on both an 18 mm and 40 mm diameter XS MCP detector with strip pitch of 640 microns and read out with multiple 32 channel "Preshape32" ASIC amplifiers (developed at Rutherford Appleton Laboratory). Each strip electrode is continuously digitized to 12 bits at 50 MHz with all 64 digital channels (128 for the 40 mm detector) transferred to a Xilinx Virtex 5 FPGA. We describe how events are detected in the continuous data stream and then multiplexed into firmware modules that spatially and temporally filter and weight the input after applying offset and gain corrections. We will contrast a windowed "center of gravity" algorithm to a convolution with a special centroiding kernel in terms of resolution and distortion and show results with < 20 microns FWHM resolution at input rates > 1 MHz.
authors.affiliation: Space Sciences Laboratory, Univ. of California, Berkeley, 7 Gauss Way, Berkeley, CA. 94720-7450, U.S.A.
authors.forename: John
authors.initials: J
authors.lastname: Vallerga
authors.forename: Anton
authors.initials: A
authors.lastname: Tremsin
authors.forename: Rick
authors.initials: R
authors.lastname: Raffanti
authors.forename: Oswald
authors.initials: O
authors.lastname: Siegmund