SILICON PHOTOMULTIPLIER SiPM GAIN CALIBRATION IN DETECTORS
Publication Date: 2015-Oct-19
The IP.com Prior Art Database
An iterative gain update algorithm for SiPM gain calibration in a light sharing detector block construct is disclosed Number of anodes or sensors is less than the number of crystals in the detector block construct The objective of the algorithm is to adjust the anode cathode bias combination or over voltage such that measured energy peak for each crystal reaches a predetermined target value As depicted in flow diagram of Figure 1 the algorithm comprises measuring energy peaks from default gain setting computing relative errors of measured peaks from the predetermined target value computing the relative gain required to reach the predetermined target value computing the required anode digital to analog converter DAC changes to achieve the intended relative gain and repeating until the required anode DAC change is smaller than a threshold value
The present disclosure relates generally to silicon photomultiplier (SiPM) gain calibration in detectors and more particularly to an iterative gain update algorithm for SiPM gain calibration.
Silicon photomultipliers (SiPM) are single photon sensitive devices built from an avalanche photodiode (APD) array disposed on a silicon substrate. Detectors based on photomultiplier photo-sensors require gain or energy calibration in order to properly operate.
However, there are multiple instances where individual anode or sensor response is inaccessible and cannot be measured directly. Such instances are common with SiPM based detector constructs and the response or output is weighted and combined in an application-specific integrated circuit (ASIC) for calibration.
It would be desirable to have an improved technique for SiPM gain calibration in detectors.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 is a flow diagram of steps of an iterative gain update algorithm for silicon photomultiplier (SiPM) gain calibration in a light sharing detector block construct.
Figure 2 is a graphical representation of conversion from delta gain on X axis and delta anode digital to analog converter (DAC) on Y axis, using a quadratic equation.
Figure 3 depicts examples of relative energy peak target values for crystals of the detector.
Figure 4 is a table showing an example of pseudo inverse of matrix of coupling factors.
Figure 5 depicts an example of 12 fitted slopes for 12 crystals of the detector.
Figure 6 shows the results for all crystals, when each of the six anodes in device is varied individually and energy peaks were measured.
Figure 7 is a table of slopes' values made symmetrical and scaled coupling factors.
An iterative gain update algorithm for SiPM gain calibration in a light sharing detector block construct is disclosed. In silicon photomultiplier (SiPM) detector calibration, in order to set crystal photo peaks to their pre-assigned energy targets, the overvoltage of anodes in a detector are iteratively adjusted by amounts calculated from the residuals from their respective targets. The adjustments are obtained by solving a set of simultaneous linear equations. The simultaneous equations model the overall crystal response by summing the weighted responses from all anodes stimulated by light originating from the specific crystal. Depending on the anode location relative to the crystal of interest, a fixed portion of the original amount light arrives at a specific anode. The amount depends on the detector block construct, such as crystal surface finish, crystal dimensions, optical indices of the interfaces and light guide. The term coupling, which is used as weights in the simultaneous equations, is usually used to describe the amount of light transferred from the crystal of interest to the anode.
The objective of the algorithm is to adjust the anode/cathode bias combina...