Paralleling of Preamplifier Input Stages for a Low-Noise, Wideband Termination of Low-Impedance Transmission Lines

A new concept of paralleling input stages was developed to meet the requirements for a low-noise, wideband preamplifier that matches the transmissionline impedance of ultrahigh-sensitivity fission counters. The prototypic preamplifier consists of four dual-feedback-path amplifiers and a summing amplifier. It has an 18-pA/✓Hz equivalent input noise current density, a 60-MHz bandwidth, a 25-Ω input impedance, and a 5-kΩ transimpedance.