Semilogarithmic Amplifier System

This report describes an amplifier system having the capability of compressing several decade pulse height ranges into several linear step gain ranges covering only a single decade. Rather than employing the usual frequency, voltage, and temperature dependent low voltage semiconductor switching and conduction characteristics, this amplifying system utilizes the reproducible, easily calibrated, abrupt, high level limiting characteristics of a transistor operational feedback amplifier. The several cascaded stages of this amplifier, whose individual outputs drive a pulse adder, use these abrupt, high level limiting characteristics to determine the boundries between several well defined linear step gain ranges as a function of pulse amplitude. The gain in each of these ranges is established by that gain available prior to the point where limiting occurs in the amplifier system. Such an amplifying system has great application in the measurement of wide range nuclear or other pulse height spectra, where the relatively poor resolution uniformity of multichannel analyzers either dictates an unreasonable number of available channels or the use of some sort of compression amplifier. The plot of Fig. 1 clearly displays this resolution nonuniformity.