Acquisition and processing of multiparametric information from a pixel matrix

Abstract

Acquisition and Processing of Multiparametric Information from a Pixel Matrix P.F. Manfredi 1,2 J.E. Millaud 1 , V.V. Sushkov 1 Lawrence Berkeley National Laboratory 1, Cyclotron Rd-Berkeley, CA 94720 Pavia University and INFN-Pavia (Italy) Abstract This paper addresses the design of a system intended to readout multiparametric information from a matrix of pixels. The system presented here acquires the charge associated with the signal and provides a timing information from each pixel. Although it lends itself to a broad range of time- correlated imaging situations involving any kind of pixel matrices, the design constraints assumed here are particularly tailored to the application with pixels that sense the output charge distribution from a Micro Channel Plate (MCP). The combination of a microchannel plate and a pixel matrix is an extremely versatile detector and the readout system must be able to fully exploit the intrinsically high position resolution and time accuracy featured by the MCP The behavior of the readout system described in this paper is based upon advanced concepts to meet the above application requirements and is believed to provide a significant functional improvement over the conventional pixel systems. Work funded by US DOE under contract DE-AC03-76SF00098 One more example of a situation demanding accurate timing is the principle of three dimensional imaging based upon time- domain reflectometry associated with a pixel matrix. The idea of multiparametric acquisition from pixel matrices can be extended to more complex cases including other signal features, for instance, shape-related parameters. The present paper aims at discussing the design of a multiparametric system to be associated with a pixel matrix. As already pointed out, the system, though not restricted to this application, is conceived to meet the requirements set by the detector shown in fig.1, consisting of an MCP read out by a matrix of electrodes deposited on an insulating substrate. I. I NTRODUCTION The introduction of pixel detectors in tracking applications has set the demand for high density readout electronics consisting of one cell per pixel with the task of identifying the address of the pixels where signals above a preset threshold are recorded. The same readout electronics associated with a histogramming memory to build-up the distribution of counts recorded by each pixel in a fixed time interval is employed in imaging applications. In either case, only the presence of a signal is recorded by the readout system [1], [2], [3], [4]. There are, however, situations, where signal-related parameters are to be extracted and a readout is able to acquire and process multiparametric information is required. For example, if the value of the charge associated with the signal is available, it is possible to increase the position resolution well beyond the geometric size of the pixel by using an interpolation approach. Signal timing is important in several time-resolved or time-correlated position sensing and imaging applications. Examples of situations requiring both position and time information are provided by Time-of-Flight mass spectroscopy and by the analysis of reactions initiated by photo ionization (molecular dissociation), where the photo ionization produced by laser light results in fragmentation. Multi hit time-resolved detection may be required in this case Figure 1: Micro Channel Plate read out by a pixel matrix The detector of fig.1 is extremely versatile. By a suitable choice of the photocathode material or of the input converter, it may be employed to detect photons on a very broad range of wavelengths, from infrared to low energy X-rays as well as particles of different nature. The intrinsic position resolution of an MCP is substantially better than that of a semiconductor pixel detector. The only way of retaining this feature by a pixel readout of the type shown in fig.1 is by making use of position interpolation. A spatial resolution five to ten times better than the geometric size of the sensing electrodes in fig.1 can be reasonably expected from this approach. A substantial improvement over the existing imaging techniques may result in such an important field like mammography.