A fast low noise photomultiplier tube amplifier

The authors present the front-end amplifier for detectors at the Superconducting Super Collider which use a photomultiplier tube (PMT) readout. The amplifier is able to process PMT output signals of 16-ns duration within a 94-dB dynamic range (between 15 mA and 300 nA). To achieve this performance both a high-gain and a low-gain signal processing path are used, with gains in a ratio of 32:1. The PMT output current is conditioned by two current amplifiers and then integrated by two fast, low-noise integrators. The signal baseline is restored in order to avoid any loss of information when a high energy crossing is immediately followed by a very low energy one. The outputs are connected to switched capacitor arrays which are read out after a trigger decision and digitized with a 12-bit analog-to-digital converter. Tests show: (1) a drop of 0.5% within 4 ns after the integration was completed; (2) 0.23-mV _rms noise figure at the circuit output; (3) an input impedance of 50 Ω; (4) fast baseline restoration; and (5) an output impedance matched for 100 Ω twisted pair cables, or 50 Ω coaxial cables