高场核磁共振波谱仪宽带前置放大器的研制

宽带前置放大器是磁共振仪器的重要部件，其性能决定了整个仪器X核通道的检测灵敏度. 根据射频电路理论以及磁共振波谱仪整体性能指标的要求，设计并实现了可应用于高场核磁共振波谱仪的高性能宽带前置放大器. 实测结果表明，所研制的核磁共振波谱仪宽带前置放大器在15 MHz~300 MHz频率范围内，其工作性能达到：带内增益>38 dB，带内平坦度<1.5 dB，噪声系数基本保持在1.2 dB以下，射频开关切换时间<1.5 μs，具有带内增益平坦度高，噪声系数小，发射状态下放大器前端保护电路隔离度高，以及工作状态检测电路准确、简洁的特点. 同时高场核磁共振碳和磷等杂核实验显示，利用所研制的宽带前置放大器可检测到具有较高信噪比的NMR信号.

Design of Broadband Preamplifier for High-Field NMR Spectrometers

As one of the most important part of NMR spectrometers, broadband preamplifiers determine the sensitivity of the hetero nucleus channel. On the basis of RF circuit theory and the overall parameter requirements, a broadband preamplifier for high field NMR spectrometer was designed. In the 15 MHz~300 MHz, test results demonstrate that the designed preamplifier exhibits a gain of over 38 dB，in-band fluctuation less than 1.5 dB, the noise figure less than 1.2 dB, and the switching time of RF switch under 1.5 μs. The broadband preamplifier has a good performance, as illustrated by its small in-band fluctuation, low noise figure, high isolation of protecting circuit in transmitter mode, as well as an accuracy of working condition detection circuit. Experimental results of hetero nucleus such as ¹³C and ³¹P demonstrate that the broadband amplifier has high signal to noise of NMR signals, which is comparable with those of commercial broadband amplifiers.