A new low-noise charge-sensitive micropreamplifier used in portable detecting instrument is designed through analysing the performance of CdZnTe semiconducte detectors and considering the noise character of the charge-sensitive amplifier. At normal temperature
energy resolution of the detecting system with a 3mm×7mm×3mm CdZnTe detector and the charge-sensitive micropreamplifier is 4.38% to the 59.5keV 241Am γ source.