Characterisation of analogue front end and time walk in CMOS active pixel sensor

TL;DR

This paper characterizes the time walk and analogue front end behavior of a CMOS active pixel sensor using Edge-TCT and external charge injection, before and after neutron irradiation, revealing uniform charge collection and edge effects.

Contribution

It introduces a method to measure time walk in CMOS active pixel sensors using Edge-TCT and compares results with external charge injection, including post-irradiation analysis.

Findings

Time walk below 25 ns for charges above 2000 electrons.

Uniform charge collection across the pixel, with edge effects observed.

Consistent results between Edge-TCT and external charge injection measurements.

Abstract

In this work we investigated a method to determine time walk in an active silicon pixel sensor prototype using Edge-TCT with infrared laser charge injection. Samples were investigated before and after neutron irradiation to 5e14 neq/cm2. Threshold, noise and calibration of the analogue front end were determined with external charge injection. A spatially sensitive measurement of collected charge and time walk was carried out with Edge-TCT, showing a uniform charge collection and output delay in pixel centre. On pixel edges charge sharing was observed due to finite beam width resulting in smaller signals and larger output delay. Time walk below 25 ns was observed for charge above 2000 electrons at a threshold above the noise level. Time walk measurement with external charge injection yielded identical results.