Study Of High-speed Data Acquisition System Of Low Field Nuclear Magnetic Signal

Data acquisition of nuclear magnetic resonance(NMR)signals affects the acquisition of data accurate information by NMR experiments.Acquiring the low field NMR signals becomes one of the most important problems in the design of the low field NMR instrument.A programmable system which can produce and launch pulse sequence through programming is designed for signals acquisition at different frequencies in low field NMR.The system is composed of a FPGA chip and several peripheral circuits for signal acquisition,signal emission,USB communication and generating frequency modulation signal,phase modulation signal,amplitude modulation signal,etc.Single master chip is used for implementing these functions such as timing control and data processing.The FPGA chip implements digital modules including interface,pulse generation module,digital quadrature demodulation,and digital waveform synthesis.Superheterodyne frequency conversion is used for signal reception,so different filters are used as the different Larmor frequencies.In order to realize a simplified digital quadrature demodulation algorithm,analog-to-digital converter transforms NMR analog signal into a digital signal at high speed of 80 MHz.Last,the system is verified by a lot of test with a platform composed of PC,the system,power amplifier,preamplifier and sensor.