Sporadically-driven clock-less in-pixel multi-bit energy discriminator for X-ray spectrometry CMOS PCD imagers

Abstract

A compact size and low-power multi-bit energy discriminator circuit is presented for X-ray spectrometry CMOS photon-counting detector (PCD) pixels. Because the circuit design is based on an asynchronous linear search, the discriminator with only a single-comparator classifies a sporadically incoming photon into multiple energy-bins, resulting in high spatial resolution and functionality of material-selective imaging. The proposed pixel power required to perform a minimal linear search is significantly less than the power of a conventional parallel search implemented in a flash-type discriminator. A prototype is fabricated in a 130-nm CMOS, and a 3-bit discriminator occupies only 23 x 60 m(2). The circuit dissipates a static power of 1 W with a power supply of 3.3 V (analogue) and 1.2 V (digital). The inaccuracy of energy-binning is measured to be 2.6-3.3 mV rms.