Centroiding algorithms for high speed crossed strip readout of microchannel plate detectors

Citation

Vallerga, J., Tremsin, A., Raffanti, R., & Siegmund, O. (2011). Centroiding algorithms for high speed crossed strip readout of microchannel plate detectors. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 633, S255–S258. https://doi.org/10.1016/j.nima.2010.06.181 

Keywords

• Microchannel plate detectors
• single-photon counting
• cross strip anodes
• centroiding algorithms

Brief

Imaging microchannel plate detectors with cross strip readout anodes require centroiding algorithms to calculate the centroid of each event in real time using an FPGA. 

Summary

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. The authors developed a system that uses an amplifier and analog-to-digital converter (ADC) for each strip and calculates the centroid of each event in real time using a field-programmable gate array (FPGA). This allows for a much higher input event rate by avoiding the bandwidth limitations of transferring raw data to a computer. The firmware developed for this system remaps channel numbers, subtracts DC offsets, detects events, linearizes amplitudes, applies finite impulse response (FIR) filters, calculates spatial centroids, corrects distortions, synchronizes position data, and transfers events to a downstream computer.

There is a tradeoff between the precision and accuracy of centroid determination and the event rate. Using fewer strips in the calculation improves precision, while using more strips improves accuracy. The "all above threshold" (AAT) algorithm used in this work only uses strip signals above a certain fraction of the total event charge. This method adjusts the number of strips used based on the location of the charge cloud. The interpolated convolution (IC) algorithm provides better spatial resolution and smoother distortions than the AAT algorithm by convolving the charge distribution with a bipolar kernel.

The system, tested with 18mm and 40mm XS detectors, achieved a spatial resolution of  microns at a gain of 900,000 e- per photon. The periodic distortion caused by undersampling the charge distribution was corrected in real time using a look-up table in the FPGA. The authors conclude that new ASICs could further improve the system's performance by decreasing event duration and amplifier noise.

Origin: https://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC3170860&blobtype=pdf