Optimum Signal-Processing for Pulse-Amplitude Spectrometry in the Presence of High-Rate Effects and Noise

In this paper the idea of a general signal processing system which should satisfy various pulse rate and noise requirements is explored. Optimum processing functions (weighting functions) are considered for an ideal system, and for real conditions where effects like imperfect pole-zero cancellation are present. Time-variant filters of the gain-varying class are used to realize the required optimum weighting functions of finite width. It is shown how nonfinite-width weighting functions of some time-invariant filters can be modified into finite-width functions by switching. These switched-gain time-variant filters are somewhat limited in choice of weighting functions. A general processing system can be realized employing filters with continuously time-variant elements. In particular, a gain-varying element (i.e., an analog multiplier) can be used in conjunction with an integrator to realize arbitrary weighting functions, and therefore the theoretically maximum signal-to-noise ratio. The system is time-variant only for the noise and not for the signal, so that it does not require high precision of the time-variant element. The system output is independent of the gating interval, and does not require precise timing. A method for evaluation of such systems in terms of noise, ballistic deficit and sensitivity to parameter variations is given.