Self-Adjusting Threshold Mechanism for Pixel Detectors

TL;DR

This paper introduces a self-adjusting threshold mechanism for pixel detectors that uses electrical noise as a relative measure to automatically calibrate and maintain uniform response across pixels, improving stability and radiation immunity.

Contribution

A novel digital self-adjusting threshold mechanism that corrects for spatial and temporal variations in pixel detectors without traditional calibration methods.

Findings

Simulations show comparable performance to traditional calibration.

The mechanism maintains stability over time.

It is immune to single event upsets.

Abstract

Readout chips of hybrid pixel detectors use a low power amplifier and threshold discrimination to process charge deposited in semiconductor sensors. Due to transistor mismatch each pixel circuit needs to be calibrated individually to achieve response uniformity. Traditionally this is addressed by programmable threshold trimming in each pixel, but requires robustness against radiation effects, temperature, and time. In this paper a self-adjusting threshold mechanism is presented, which corrects the threshold for both spatial inequality and time variation and maintains a constant response. It exploits the electrical noise as relative measure for the threshold and automatically adjust the threshold of each pixel to always achieve a uniform frequency of noise hits. A digital implementation of the method in the form of an up/down counter and combinatorial logic filter is presented. The behavior of this circuit has been simulated to evaluate its performance and compare it to traditional calibration results. The simulation results show that this mechanism can perform equally well, but eliminates instability over time and is immune to single event upsets.