High Dynamic Range X-ray Detector Pixel Architectures Utilizing Charge Removal

TL;DR

This paper introduces advanced high dynamic range X-ray detector pixels with charge removal techniques, significantly improving flux measurement capacity while maintaining sensitivity, suitable for synchrotron and XFEL applications.

Contribution

The paper presents novel CMOS pixel architectures with charge removal that extend dynamic range by shifting from capacitor size to digital counter depth, enabling higher flux tolerance.

Findings

Achieved flux measurement exceeding 10^11 x-rays/pixel/second.

Demonstrated pixel linearity through direct current injection tests.

Fabricated a small-scale ASIC prototype for these architectures.

Abstract

Several charge integrating CMOS pixel front-ends utilizing charge removal techniques have been fabricated to extend dynamic range for x-ray diffraction applications at synchrotron sources and x-ray free electron lasers (XFELs). The pixels described herein build on the Mixed Mode Pixel Array Detector (MM-PAD) framework, developed previously by our group to perform high dynamic range imaging. These new pixels boast several orders of magnitude improvement in maximum flux over the MM-PAD, which is capable of measuring a sustained flux in excess of 10$^{8}$ x-rays/pixel/second while maintaining sensitivity to smaller signals, down to single x-rays. To extend dynamic range, charge is removed from the integration node of the front-end amplifier without interrupting integration. The number of times this process occurs is recorded by a digital counter in the pixel. The parameter limiting full well is thereby shifted from the size of an integration capacitor to the depth of a digital counter. The result is similar to that achieved by counting pixel array detectors, but the integrators presented here are designed to tolerate a sustained flux >10$^{11}$ x-rays/pixel/second. Pixel front-end linearity was evaluated by direct current injection and results are presented. A small-scale readout ASIC utilizing these pixel architectures has been fabricated and the use of these architectures to increase single x-ray pulse dynamic range at XFELs is discussed briefly.