The Research On Large Dynamic Range Charge Measurement Circuit For The Photoelectric Multiplier Tube

The exploration and research of cosmic rays is an important means for people to unveil the mystery of the universe, finding the origin of the cosmic ray is the core problem of the current cosmic ray physics. In this connection, our physicists proposed a variety of detection means joint observation of the Large High Altitude Air Shower Observatory (LHAASO) program, the main purpose of the planned air shower core detector array (SCDA) is the precise measurement of cosmic ray air shower shaft core area of high-energy electromagnetic components. In this context, this thesis carried out the research design of charge measurement scheme based on the readout electronics of SCDA.The main task of the SCDA readout electronics system is to accurately measure the charge of the output of the photoelectric multiplier tube (PMT). In order to realize high precision and large dynamic range of charge measurement, this design uses a charge measurement scheme based on current integration method. And combined with the design index of the electronics to optimize the scheme, then takes the theoretical analysis and stimulant authentication on the current integrated circuit, the filter forming scheme and other parts of the scheme. In addition, because of the distributed arrangement of SCDA, the readout electronics is connected to the detector through a coaxial cable. In order to prevent signal reflection, this design connects the equivalent 50 ohm resistor between the front end of the readout electronics and the virtual ground of charge integral amplifier to achieve impedance matching, and the parallel impedance matching scheme is presented which is suitable for large dynamic range charge measurement circuit.Based on the study of the charge measurement scheme, from the analog circuit design, the electronics PCB layout design and the FPGA firmware design,this paper introduces the development of the readout electronics principle prototype. In the laboratory, the test system of the test system of the charge measurement circuit was set up to test the parameters such as the charge measurement range, the measurement precision and the integral nonlinearity. The test results show that the charge measurement circuit system can achieve the measurement accuracy of 1.12% in the range of 6.2 pC-8118 pC charge measurement, and its full range integral nonlinearity is 0.234%, which meets the requirements of electronic design. In addition, due to the "Virtual Earth" impedance matching scheme with parallel shunt, the readout electronics system can realize the measurement of different charge measurements by simply adjusting the ratio of parallel resistance. This function was also tested in this paper, the test results show that the circuit system has good applicability in different charge quantity input cases.