The Second Stage Noise Contribution of a Nuclear Pulse Amplifier

The noise contribution P of the second stage relative to that of the preamplifier is derived as a function of its own noise parameters, the noise parameters and gain of the preamplifier, and the elements RoCo of the coupling network. Design criteria are derived, if the second stage either precedes or follows the short differentiator. For the latter case it is shown, that a lower limit exists for P if Co is greater, and Ro is smaller than a certain critical value. The resulting time-constant RoCo, for which that lower limit is obtained, is considerably shorter than the shaping time constant T. Hence, P may be reduced if the detector current impulse is recovered from the preamplifier output step by choosing RoCo < < T, and if shaping is postponed to a later stage. The paper concludes with a short discussion of the implications which these considerations have upon the design of the amplifier stage following the first differentiator.