Novel high resolution readout for UV and X-ray photon counting detectors with microchannel plates

Until recently the spatial resolution of microchannel plate based photon/particle counting sensors has generally been limited by the accuracy of the readout technique. The accuracy of novel readouts, in particular cross strip anodes, have now reached the 6-10 mu m scale (the typical size of pores in a microchannel plate) and no longer determine the ultimate resolution limit of the detector. Although there are some issues (e.g. fixed pattern distortions seen on 5 mu m scale) to be resolved for the cross strip (XS) anodes, one of the major drawbacks of the previous generation XS readouts is the low counting rate capability (10 KHz), determined by the processing electronics, in particular by the signal amplifier ASICs. In this paper we describe a new signal processing technique which should allow for high counting rates exceeding 1 MHz with the same high spatial resolution (< 10 mu m FWHM). The slow analog sample and hold signal processing is replaced by a fully parallel signal amplification followed by digital peak detection in each output channel. The charge values in each electrode are calculated from the digitized waveforms passed into a Field Programmable Gate Array (FPGA) where the signal peak detection and event centroiding is performed continuously. A detailed model was developed in order to optimize the digital peak detection algorithms and to determine the acceptable parameters for the electronic elements for a given spatial resolution. The results of our Monte Carlo modeling indicate that the spatial resolution of fast XS anode encoding electronics. will still be better than 10 mu m FWHM.