Minimum-Noise Filters with Good Low-Frequency Rejection

A nuclear pulse spectrometer should have both low noise and minimal sensitivity to slow disturbing signals, e.g. base-line fluctuations due to long CR-couplings. A bipolar filter weight-function (or step response) with area balance is advantageous for the latter, but generally involves increased noise and/or resolving time. This paper derives the optimum area-balanced waveform giving least noise for a defined overall width. Optimum waveforms are illustrated and the noise/signal performance is compared with that of the finite-width unipolar cusp and also with several practical bipolar systems in common use.