  The CDEX (China Dark matter Experiment) is currently in the stage to upgrade
to approximately 10 kg HPGe (High Purity Germanium) detectors (CDEX-10) in CJPL
(China Jinping Underground Laboratory) and aims to detect the WIMP (Weakly
Interacting Massive Particles). Six analog signals and one inhibited signal are
outputted from preamplifier by one HPGe detector (~1 kg) of CDEX-10. The analog
signals are conditioned with two 6-us and one 12-us shaping amplifiers, and
three timing amplifiers respectively. The inhibited signal is used for trigger.
The analog signals from shaping and timing amplifiers are digitized to obtain
energy spectrum and rise-time distribution. The rise-time distribution is used
to discriminate surface, bulk, and very bulk events, which can help to supress
the background level in dark matter detection. Composed of commercial modules,
the previous DAQ (Data Acquisition Systems) is insufficient in discriminating
between bulk and very bulk events due to the limited sampling rate (100 MSPS).
Besides, as number of channel increases, the system will be simplified by
integrating the trigger logic in FPGA (Field Programmable Gate Array). In this
paper, a prototype named RAIN4HPGe is designed with pulse digitizer and readout
electronics, integrating 14-Bit 100 MSPS ADCs (Analog-to-Digital Converters),
12-Bit 1 GSPS ADCs, FPGA etc.. The RAIN1000Z1 readout module based on ZYNQ SoC
(System on Chip) is used for readout over Gigabit Ethernet. Better energy
resolution, e.g. improving from 558 eV to 474 eV @122 keV, can be achieved by
RAIN4HPGe compared to previous DAQ (Data Acquisition Systems) with commercial
solution. Moreover, the discrimination performance of bulk, and very bulk
events has been improved by RAIN4HPGe with 1 GSPS ADC.
