  The DarkSHINE experiment aims to search for dark photons by measuring the
energy loss of the electrons recoiled from fixed-target. Its electromagnetic
calorimeter is primarily responsible for accurately reconstructing the energy
of the recoil electrons and bremsstrahlung photons. The performance of the
electromagnetic calorimeter is crucial, as its energy measurement precision
directly determines the sensitivity to the search for dark photons. The
DarkSHINE electromagnetic calorimeter uses LYSO crystals to form a fully
absorptive electromagnetic calorimeter. It utilizes SiPMs to detect
scintillation light in the crystals, and its readout electronics system deduces
the deposited energy in the crystals by measuring the number of photoelectric
signals generated by the SiPMs. The DarkSHINE electromagnetic calorimeter aims
to operate at an event rate of 1-10 MHz, detecting energies ranging from 1 MeV
to 1 GeV. To meet the requirements of high energy measurement precision, high
event rate, and large dynamic range, we have researched and designed a readout
electronics system based on dual-channel high-speed ADCs and a customized DAQ.
The front-end amplification part of this system uses low-noise trans-impedance
amplifiers to achieve high-precision waveform amplification. It successfully
achieves a dynamic range up to a thousandfold through a double-gain readout
scheme. The digital part uses 1 GSPS high-speed ADCs to achieve non-dead-time,
high-precision waveform digitization. The DAQ part uses JESD204B high-speed
serial protocol to read out the signal from ADC, and transmit it to PC software
for processing and storage. Test results show a signal-to-noise ratio greater
than 66 dBFS and an ENOB greater than 10.6 bits. Energy spectra measurements
have been conducted using LYSO crystals and SiPMs, and an energy resolution of
5.96% at the 2.6 MeV gamma peak of Th-232 has been achieved.
