Design of Equivalent Sampling Method Based On Vernier Caliper For Chang'E-5 LRPR

Lunar Regolith Penetrating Radar (LRPR) is a high resolution penetrating and imaging radar, which is a main payload of Chang'E-5. The primary aim of LRPR is to survey the lunar regolith thickness and the subsurface structure of landing area. The aim is achieved by transmitting pulse and receiving echo signal. As the width of the transmitting pulse is picosecond level, it is difficult to achieve real-times sampling of echo signal on the circuit. Equivalent sampling is adopted. The commonly used methods of equivalent sampling are implemented by the delay chip or hardware circuit. This article points out the disadvantages of the two methods, then designs a method based on the principle of Vernier Caliper. The method with strong adaptability is implemented by PLL based on FPGA, which has high reliability and high precision. There is no extra expense in hardware circuit with this method, and the delay accuracy can be adjusted.