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针对高分辨核磁共振波谱仪需要锁场信号锁定磁场的要求,提出采用DDS技术产生稳定、高分辨的锁场信号方案。方案利用FPGA为系统控制核心控制DDS电路,使DDS电路同时输出锁场前端信号和接收机本振前端信号;2个前端信号经过椭圆低通滤波器、功率放大和可变衰减之后,输出频率可变、性能稳定、被调制的锁场信号。实验证明在保证稳定性和高分辨的特性下,采用该方案的波谱仪能够简化系统结构,并对将来研制800 MHz波谱仪有指导意义。
Aimed at the requirement of high-resolution nuclear magnetic resonance spectrometer that the lock field signal needs to be locked, a stable and high-resolution lock field signal scheme using DDS technology is proposed. The program uses FPGA to control the DDS circuit as the core of the system control so that the DDS circuit outputs the front-end signal of the lock field and the front-end signal of the local oscillator of the receiver at the same time. After the two front-end signals pass through the elliptic low-pass filter, the output frequency can be Variable, stable performance, the modulation of the lock field signal. Experiments show that in the guarantee of stability and high resolution characteristics, using the program of the spectrometer can simplify the system structure, and for the future development of the 800 MHz spectrometer instructive.