A New Design of NMR Signal Receiver Based On ALE Method

In recent years more and more NMR instruments are applied in industrial fields [1] . Due to the fact that the signal is weak for NMR measurements and there are large amount of noise arising from work environment, lots of efforts have been made to improve the Signal-to-Noise Ratio (SNR) of receiver. Adaptive Line Enhancer (ALE) method is an adaptive self-tuning filter capable of separating the periodic and stochastic components in a signal. Such methods have been used in various applications, including communication systems, biomedical engineering, and industrial applications. In recent years, a based ALE method NMR receiver is designed, which is shown in Fig1.

Simulations and experiments showed that ALE method has prominent performance on noise suppression, envelope recovery [2] . However, this receiver system combined with ALE and DPSD method is difficult to implement with digital processing chips, because there are two different filters placed in series. Let's consider that the adaptive filter length is M and LP FIR length is N. As L-values data is received from ADC chip, the computational complexity of processing data is O(MNL). It will take too much computing time and require lots of resources on chip. Therefore, we adjusted the structure of receiver system which is shown in Fig2. Firstly, the data x(n) from ADC needs to be multiplied by cos(2 π fn) to get xi(n) just as the data processing in traditional DPSD method. Then ALE method is applied to the data filtered by LP FIR. If the working conditions of NMR instruments do not change significantly, one convergence adaptive filter can be made. Finally, the LP FIR in DPSD receiver system is replaced by the convergence adaptive filter and the new receiver system is fulfilled. This receiver system can obtain higher SNR data just having the same computational complexity (O(ML)) as traditional DPSD receiver. It makes the NMR signal receiver based on ALE method easy to be developed on digital processing chip and widely used in NMR instrument, which can be used to obtain high SNR data.