Abstract
In the present study, a data acquisition system for a GEM one-dimensional array detector is presented. The detector system is to measure the trajectory of photoelectrons produced by cosmic rays. The GEM array detector for the present project has multi-signal channels. The TDC units are built using the FPGA on-board chips based on a Two-ring oscillator algorithm. The timing signals and the energy signals are fed to the time-to-digital converter (TDC) units and Amplitude-to-Time Converter (ATC) units respectively. Therefore, the resolution of TDCs is a very important parameter for the present application. The front-end units are implemented using an application-specific integrated circuit (ASIC) design. The data acquisition unit is implemented using commercial field programmable gate array (FPGA) circuits. The TDC unit using the FPGA logic gates is based on a Two-ring oscillator algorithm. For multi-channel GEM detector, there is not enough clock input port at a FPGA chip. As a result, an error finder unit or dedicated input clock buffer(IBUFG) is used and the number of counter has to be decreased to save the resource of FPGA. The FPGA configuration is designed using a hardware description language (HDL), similar to that used for the front-end ASIC. The TDC units, and the communication and control logics among channels are integrated using the built-in features of the FPGA board. The FPGA based system is then linked to a personal computer for data analysis. The control signal from the computer and the data communication are using USB port. Measurements using simulated signals have been performed. Results indicated that the FPGA-based TDC waveform has a good linearity and indicated that the system is very flexible for measuring parameter adjustments under various experimental conditions.