The performance of a high speed pipelined photomultiplier readout system in the Fermilab KTeV experiment

The KTeV fixed target experiment at Fermilab is using an innovative scheme for reading out its 3100 channel CsI electromagnetic calorimeter. This pipelined readout system digitizes photomultiplier tube (PMT) signals over a 16-bit dynamic range with 8-bits of resolution at 53 MHz. The crucial element of the system is a custom Bi-CMOS integrated circuit which, in conjunction with an 8-bit Flash ADC, integrates and digitizes the PMT signal charge over each 18.9 ns clock cycle (53 MHz) in a deadtimeless fashion. The digitizer circuit is local to the PMT base, and has an in-situ charge integration noise figure of 3 fC/sample. In this article, the readout system will be described and its performance including noise, cross-talk, linearity, stability, and reliability will be discussed.