  We are planning a future gamma-ray burst (GRB) mission HiZ-GUNDAM to probe
the early universe beyond the redshift of z > 7. Now we are developing a small
prototype model of wide-field low-energy X-ray imaging detectors to observe
high-z GRBs, which cover the energy range of 1 - 20 keV. In this paper, we
report overview of its prototype system and performance, especially focusing on
the characteristics and radiation tolerance of high gain analog ASIC
specifically designed to read out small charge signals.
