SIGNAL AND NOISE RESPONSE IN VARIOUS CONFIGURATIONS OF CHARGE SENSITIVE PRE-AMPLIFIERS

Four different configurations of charge sensitive preamplifiers were analysed. Three configurations were standard charge loops with Miller effect and differed by connection of input stage. The fourth configuration was a Deši bootstrapped follower. Equivalent circuits were drawn, transmittances for signal and various noise sources were found and some conclusions derived. At time constants used in Si(Li) spectrometry none of the configurations offers advantages in signal-to-noise ratio. However at very short time constants the deviation of the presented analysis from classical charge preamplifier formulae is more pronounced. Simple examples of formula applications to the analysis of some preamplifier problems are given. The presented analysis of therge sensitive preamplifiers differs from previous theories by the fact that the full equivalent circuit of the input FET is considered and not only the input admittance. This modifies the results for very short time constants. © 1978.