Research On Time-to-digital Converter Technology Based On FPGA

In recent years,with the quickening pace of urban life and ever-increasing work pressure,the incidence of cancer in China has been on the rise.If prevention can be implemented as soon as possible,the incidence of cancer will be greatly reduced.Positron Emission Tomography(PET)is an effective and non-invasive imaging diagnostic technology recognized at home and abroad.The use of accelerator radiation therapy for patients,it has the characteristics of slight radiation damage to the human organ tissue,short treatment cycle time,high cure rate.At present,the main problem that PET system needs to solve is to optimize the imaging system,improve the sensitivity of the system,increase the resolution of the image,and reduce the interference caused by the observation as much as possible.To achieve accurate positron annihilation,the system requires highly accurate time resolution.Time-ofFlight(TOF)has been proven to solve the above problems.In addition,the circuit used for flight time information measurement should have the following features: simple structure,small size and other advantages;scalability and repetitive programming flexibility.This paper selects the CYCLONE III chip produced by Altera Corporation.The design route adopts a combination of coarse counting and fine time measurement,in which the measurement of coarse time particles is implemented by a binary counter.Time stamping can effectively avoid the problem of time walking.The realization of the fine time measurement uses the adder IP core to construct the carry chain to realize time interpolation.Using the dedicated delay path inside the adder can achieve high test accuracy.Compared to serial communication,the communication speed is slow and the real-time performance is poor.This paper adopts USB2.0 conversion to data transmission interface,this article adopts USB2.0 conversion to data transmission interface,rapidly increasing the data transmission rate,saving a lot of time.The time measurement results were analyzed by code density method and cable delay line method.The resolution was better than 50 ps,the measurement accuracy was 46 ps,and the dynamic range was 400 ns.DNL is between-1LSB ~ +1.5LSB,and INL is between-1.5LSB ~ +1.5LSB.