Signal Shaping and Tail Cancellation for Gas Proportional Detectors at High Counting Rates

A low noise, wide bandwidth preamplifier and signal processing filter were developed for high counting rate proportional counters. The filter consists of an eight pole Gaussian integrator with symmetrical weighting function and continuously variable shaping time, 𝑡ₛ, of 8 ns to 50 ns (FWHM) preceded by a second order pole/zero circuit which cancels the long (1/𝑡) tails of the chamber signals. The preamplifier is an optimized common base input design with 2 nsec rise time and an equivalent noise input charge of < 2000 rms electrons, when connected to a chamber with 10 pF capacitance and at a filtering time, 𝑡ₛ, of 10 ns.