Design Of X-ray Pulsar Photon's Arrival Time Measurement Circuit

X-ray pulsar navigation is a kind of autonomous navigation methods in deep space in the future.As X-ray pulsar signal is the source of navigation,X-ray pulsar navigation has many advantages,such as autonomous navigation?unrestricted use rights?ability of providing high resolution time reference.For this reason,America?European countries?Japan and many other countries have launched a study of X-ray Pulsar navigation.X-ray pulsar pulse photon arrival time as one of the critical parameters for pulsar navigation,has an important impact on the pulsar navigation.X-ray pulsar photon arrival time measurement has some features:high accuracy?wide dynamic range and so on.So far,there are no time measurements circuits of X-ray pulse photons arrival.This paper comes from the project of X-ray joint detector time measurement circuit,and the purpose is to study the possible use of a pulsar of X-ray photons program in spacecraft navigation systems.In order to solve the time measurement circuit problem that is difficult to obtain a large dynamic and high resolution simultaneously rate,and time measurement circuit techniques and methods have been studied at first.There are many methods,including counter technology,current integration technology,time amplification technology and calipers,converting time to digital data.Due to limitations of the measuring technique principle?device performance?or other aspects of the process are unable to meet the X-ray pulsar time of arrival measurement design requirements;the measurement's accuracy and dynamic range of TDC chip both meet X-ray pulsars photons arrival time measurements design requirements,but it couldn't measure multi-channel time.In this paper,based on TDC delay unit method?coarse time measurement and fine time measurement combining technique has proposed.TDC(Time-Digital Converter)circuit is designed on FPGA(field programmable gate array)chip of Xilinx Virtex-II Pro series.TDC circuit measures time by the number of modules,including coarse time measurement modules,fine time measurement modules,data caching module,multi-channel controls and other components.Found in experiments FPGA underlying structure traces on the circuit timing produce delay ns or ps.In order to overcome the impact of time measurement because of the alignment delay,through semi-manual and semi-automatic place wire invoke Slice logic unit to improve interpolation techniques,,and a fine time in the shortest possible time latch to ensure the accuracy of the time data.The design has high accuracy measurement,wide dynamic range and other advantages,and X-ray photons as pulsars arrival time conducted a preliminary exploration.