Design of Waveform Digitizing Front-end Electronics for a Prototype Multi-purpose TPC at CSNS Back-n

Multi-purpose Time Projection Chamber (MTPC) at the Back-n white neutron source of China Spallation Neutron Source (CSNS) is aimed at the measurements of neutron-induced light charged particles or fission particles and neutron resonance radiography. The prototype MTPC is completed as a verification version with 1519 anode channels. A flexible integrated waveform digitizing front-end electronics based on off-the-shelf components was designed to read out anode signals. The front-end electronics are divided into pre-amplifier module (PAM) and analog to digital module (ADM). PAM integrates the anode charge signals and converts them into differential signals. ADM performs analog waveform digitization, digital filtering, online data processing, and packaging. PAM is connected to ADM via a flexible printed circuit (FPC) and the PAM can be replaced according to different requirements of detectors. When digitizing up to 64 channels at 40 MHz, the power consumption is around 140 mW per channel. The performance of the front-end electronics has been tested in the lab. The integral nonlinearity (INL) is less than 0.35% with a 2.8 pC dynamic range, and the average equivalent noise charge without any input load is around 0.76 fC and the maximum is less than 1.3 fC. The readout electronics has been performed a joint test with the prototype MTPC. By analyzing collected anode signals, the 3D-track of neutron-induced light-charged particles was successfully reconstructed. These results indicate that the front-end electronics works well and can satisfy the requirements of the prototype MTPC.