A 1024×8 700ps time-gated SPAD line sensor for laser raman spectroscopy and LIBS in space and rover-based planetary exploration

Abstract

In this paper, we present an all-digital, 1024x8, time-resolved SPAD line sensor designed for time-resolved laser Raman spectroscopy and laser induced breakdown spectroscopy (LIBS). The block diagram of the system is shown in Fig. 6.7.1. The sensor consists of 16 groups of 64x8 SPAD arrays with fast readout interface electronics. The SPAD gate width and its delay are controlled by a combination of off-chip (Maxim DS1020, 1ns/tap) and on-chip delay lines (250ps/tap) resulting in a temporal resolution of 250ps through typical scan ranges of 32ns. Properly balanced binary trees allow less than 98.5ps skew variation across the entire chip. The proposed line sensor has a fill factor of 44.3% with a photon detection probability (PDP) of 21% at 475nm at an excess bias of 3.5V. The 24.6mm long focal plane matches the format of a typical detector that would be used at the output of a Raman spectrometer (e.g. CCD), allowing the observation of the entire Raman spectrum without the use of any moving parts, thus reducing complexity, overall power consumption, and weight.