Optimization and Performance Characterization of the Second Generation Fermilab Constant Fraction Discriminator Readout ASIC

TL;DR

This paper details the design, optimization, and testing of the second-generation Fermilab FC-FD ASIC, achieving high-precision timing and position measurements for LGAD sensors without needing time-walk correction.

Contribution

It introduces the FCFD1.1 ASIC with improved design features that enhance performance and insensitivity to signal amplitude variations for LGAD readout applications.

Findings

Time resolution of ~40 ps achieved

Position resolution of ~15 micrometers demonstrated

Effective performance with beam particles over active sensor area

Abstract

We present the optimization and performance characterization of the second-generation Fermilab Constant Fraction Discriminator ASIC (FCFD), designed for the readout of AC-coupled low-gain avalanche detector (LGAD) strip-sensors. The FCFD is explicitly engineered to be insensitive to signal-amplitude variations, thereby removing the need for time-walk correction that is required in other LGAD time-stamping readout ASICs. This updated version, referred to as FCFD1.1, incorporates several enhancements over the first iteration to address key challenges in AC-coupled LGAD front-end design. We outline the primary readout-ASIC design considerations for these applications, describe the methodology used to evaluate critical sensor and system parameters, and summarize the additionally implemented features. Performance measurements using injected charge signals and minimum-ionizing particles in test-beams demonstrate a time resolution of approximately 40 ps and a position resolution of roughly \SI{15}{\micro\meter} when tested with beam particles uniformly over the active area of the sensor.