The Design Of Excitation Part Of Pulse NMR

Nuclear magnetic resonance (NMR) became a new technology in 1946. In a short period of time, the rapid development of this technology demonstrates that it has great vitality. It mainly develops to two directions of Spectroscopy and Nuclear Magnetic Resonance. This paper mainly describes that the excitation of the part of pulse, power amplification and the interface circuit in thepulse NMR.Previously the sequence generator generates the pulse width has the limited scope, while the rising edge and falling edge pulse not steep, just for a simple multi-pulse sequence. With the development of digital electronic technology, the system of excitation signal source also put forward higher requirements, making the signal digitally-based approach to become a leading trend.With the extensive application of pulse NMR, the design of pulse excitation also put forward higher requirements in this system. This paper mainly achieves the design of a programmable sequence generator based on CPLD in thepulse NMR system, and the working principle and process of the circuit are described in detail. Then it gives the experimental waveforms and the experimental data, and some error analysis for the experimental results. It also takes the application of mature technologies of DDS to complete the output wave of sine. The last, it use of multiplier chip achieve the function of waveform modulation. Power amplification is used to make the stimulate signal for a further amplification. In addition to, this paper also introduces the design of the interface circuit and it can successfully implement of the conversion and transmission of data between CPLD and the external devices.This design can generate excitation signal pulse width of 1us-10ms, and pulse interval can be adjusted within 10us-10s. The width of output pulse in a cycle to 100ns step size can be adjusted. After modulating with the high frequency signal and amplification, it takes the excitation signal to the sample can produce a clear magnetic resonance signal. So it meets the experimental requirements fully.Throughout the experiment and the results show that this method of based on the CPLD is high speed, efficient and versatility.