Analysis And Study Of Low Field Pulsed Nmr Signals Digital Receiver Platform

The performance of signal reception circuit is one of the key factors for the realization of low-field NMR(nuclear magnetic resonance) signals. Because of low field strength, the NMR signal is quite weak and is of poor SNR(Signal to Noise Ratio). With a view to this, a digital receiver for nuclear magnetic resonance is described in this article. It has a special design based on the characters of low-field NMR.The function blocks of the low field NMR circuit system are analyzed at first. The detail frame chart of reception circuit is given. An optimize design is establish to verify corresponding problems.Secondly, a direct digital synthesized RF pulse module, a Numerically Controlled logic module and a high-speed data acquisition for NMR receiver are described in this article. The design of hardware and software is given in detail. The phase and frequency of pulse gotten form this system is of high precision and good stability. Advantages of these module include high dynamic range and perfect balance between the quadrature channels.In view of the weak signal and its poor SNR. several schemes of digital quadrature detection are described in detail. Dynamic simulations are made for the analysis of the states. The characters are given after discussions and comparisons.Finally, error in the digital processing is analyzed. The simplified analysis model and the experimental results are given.