Digital nuclear magnetic resonance signal source

Abstract

The invention relates to a measuring device or apparatus for nuclear magnetic resonance, concretely relates to a frequency generating device of nuclear magnetic resonance spectrometer, namely a digitalized nuclear magnetic resonance signal source, when the signal source ignites the nuclear self-rotating system of the sample, the sampling signal in receiving channel and the igniting signal in emitting channel are started at the same time, and the difference of igniting signal frequency and sampling signal frequency is not less than the 1 / 2 of spectrum width of nuclear magnetic resonance. Its merits lie in: it can generate radio frequency signal of the sample self-rotation system, it simplifies the design, avoids the dispersant signal in the resonance because of DDS, guarantees the phase interference of received nuclear magnetic signal.

Description

technical field [0001] The invention relates to a nuclear magnetic resonance measuring device or instrument, in particular to a frequency generating device of a nuclear magnetic resonance spectrometer, that is, a digital nuclear magnetic resonance signal source. Background technique [0002] In NMR spectrometers, the signal source, that is, the frequency source, is used to generate a radio frequency signal that excites the nuclear spin system of the sample, and is usually also used as the local oscillator (LO) signal of the heterodyne receiver. At present, most commercial NMR signal sources use analog synthesis technology to realize frequency synthesis and phase-locked loop technology. A typical example is the frequency source product series of PTS (Programmed Test Sources, Inc). In order to obtain the selective pulse required by the magnetic resonance experiment, the digital-to-analog converter (DAC) is generally controlled by an external computer to generate an amplitude ...

AI Technical Summary

Problems solved by technology

However, DDS adopts digital frequency synthesis technology, which has the following disadvantages in the application of nuclear magnetic resonance: 1. Most DDSs use ROM waveform tables to generate signals. Due to the limitation of integrated circuit technology, the scale of ROM tables is impossible. If it is made large enough, generally only the high bit of the phase accumulator is used to address and output it, so the output spectrum contains spurious signals generated by the phase truncation error of the DDS device

The spurious signal caused by the phase truncation error is phase coherent in each acquisition of the NMR signal, so its influence cannot be reduced by accumulation

2. DDS uses a high-speed DAC to generate signals, so that its output spectrum is also mixed with spurious signals caused by the limited word length effect of DAC and nonlinearity.

If the above two kinds of spurious signals are mixed into the local oscillator of the receiver, it will inevitably produce false peaks in the received NMR spectrum, thus limiting the application of DDS in the NMR spectrometer system

3. Affected by its internal clock speed, DDS devices can only generate lower frequency signals. In order to obtain higher frequencies, a large number of analog mixers (mixer) and analog frequency synthesis circuits are still used in the usual design Realize the frequency multiplication output of the signal, and cannot realize the frequency adjustment in the broadband range

Although some people use multi-channel DDS modules and data strobes to obtain relatively high frequency output by interpolating data points, multi-channel DDS modules will inevitably increase peripheral devices, resulting in a significant increase in cost, design complexity, and power consumption.

4. In terms of hardware, many existing DDSs use slow buses such as (VME, ISA, etc.) to access DDS, and cannot quickly switch frequency and phase

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