A dosimeter for space ionization radiation field is developed, energy deposited in the sensitivity volume of
ionization chamber induces an output current signal as weak as 10-14A, and the dynamic range of the signal is very high.
Now, an ionization chamber is designed and a variable gain current feedback preamp module is designed for the weak
output current amplification is connected to output of the ionization chamber anode. The amplifier module includes I-V
converter with T shaped resistance net, zero correct circuit, low pass filter, voltage linear amplifier circuit, gain control
circuit and voltage output circuit. A complete analysis of this current preamp with respect to its circuit structure, dynamic
properties, its equivalent input noise and the temperature effect is given. The effects of stray impedances on the behavior
of the current feedback preamp are taken into account and the techniques necessary to achieve an optimum stable
electrometer, with respect to noise, Dc drift, leakage currents, are applied. Experiments show that the energy of dosimeter
deposited in the sensitivity volume of ionization chamber induces an output current signal as weak as 10-14A, the current
preamp can detect weak current effectively with the range from 100fA to 10μA through switchable gain.