Some Key Technologies About Time-to-Digital Converter Based On FPGA

As one of the seven basic physical quantities, time plays an important role during the development of the physics. Different informant of the particles, such as the momentum, the mass etc. can be calculated by time information in the particle physics experiments. So time measurement is very useful for particle identification. Along with the particles being detected are smaller and smaller and the energy of the accelerators is higher and higher, the resolution of time measurement is required to be higher and higher which is to be picosecond.In the years, various kinds of time measurement methods appear and the resolution becomes higher and higher. According to the development platform, the technical route is mainly divided into two types, ASIC TDC (such as HPTDC designed by CERN) and TDC based on FPGA. Compaired with ASIC, FPGA is more flexible, reconfigurable and developed using shorter time, which promotes the TDC based on FPGA vigorous development. However, the TDC based on FPGA is only at the level of research and hasn’t been applied in the practical application. Its function is not complete and cannot meet some special requirements for the particle physical experiment. Some functions are needed shown as follows. For improving the time-walk effect, TDC should be able to measure the pulse width and the data analysis can use this information to compensate time measurement. In the experiment with trigger system, the data which are read need to be matched with trigger signal. This needs that the electronics has the trigger matching function. Some TDC applications are in the radiant environment, such as the space application, when being placed near the detector. This requires the devices are hard radiation to ensure the system’s stability and reliability. This thesis introduces the work about the function expansion of the TDC based FPGA. The thesis is arranged as follows:In chapter one, it introduces the history and development of the TDC based on FPGA. It classifies the methods and describes the principles simply.Chapter two first introduces the time measurement method which is coarse time measurement combing with fine time measurement and using the carry line resource of Xilinx FPGA to implement high resolution time measurement. Next, it introduces two kinds of method to measure pulse width. The first method applies two same TDC channels to measure leading edge and trailing edge. The second method measures both leading edge and trailing edge in only one TDC channel. Finally, a summary is given and the test results are shown.Chapter three introduces a trigger matching mechanism which is based on Content Addressable Memory (CAM). It describes the principle and implementation in detail.In chapter four, error tolerant is considered about SRAM FPGA when it works in the irradiant environment. This consideration is focus on FPGA’s static memory which will have single particle effect when in irradiant environment. It corrects the soft errors happened in the static memory in real time, such as single event upset (SEU), multiple bits upset (MBU). This function can enhance the FPGA’s reliability and stability when working in the irradiant.In chapter five, the temperature characteristic of FPGA is measured and a method is introduced about compensating TDC using the temperature parameter. Chapter six describes a standardized module which integrates the above functions. This module is based on VME interface. Lots of tests are done and the results are shown in this chapter.Chapter seven introduces the TDC’s application in Compressed Baryonic Matter (CBM) experiment in Germany. The system of the CBM experiment and its time-of-Flight (TOF) detector is described and a FPGA TDC module is designed for it. The design and results about the FPGA TDC are also introduced.Chapter eight gives a conclusion and introduces the following work needed to done in the future.