The Design of the Photon Readout Electronics for nEXO

nEXO is next-generation neutrino-less double beta decay search (0νββ) experiment based on a 5 ton liquid-Xe TPC enriched with Xe-136, and is designed to achieve a sensitivity to 0νββ of T_½ ~ 10²⁸ yr. The total energy resolution goal of nEXO is σ_E/E = 1% at the Q_ββ, and consists of contributions from the charge and photon signals. The nEXO photon readout electronics system (PRE) has several requirements in order to achieve sensitivity goal: severe constraints on radiopurity and outgassing, excellent single photon resolution (despite SiPM capacitances as high as 8 nF/cm²), and enough segmentation to identify Bi-214 decays. These challenges have led to a design based on cryogenic ASICs inside the TPC to maximize signal readout performance and vastly improve radiopurity. In this talk we will describe the nEXO PRE design in detail, and highlight the design decisions that were made to produce a solution to the numerous challenges in the photon readout for nEXO.