JPH0321490Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an automatic gain control device suitable for use in a nuclear magnetic resonance apparatus (NMR apparatus).

[Conventional technology] In an NMR device, the
It is necessary to adjust the gain of the receiving circuit as appropriate so that the amplitude of the NMR signal falls within the dynamic range of the AD converter.

Conventionally, preliminary measurements were performed by reducing the gain of the receiving circuit in advance, the operator determined the magnitude of the NMR signal at that time, reset the gain of the receiving circuit accordingly, and then measured again. We check whether it is within the appropriate range and repeat this process until the gain is appropriate.

[Problems to be solved by the invention] Since such conventional methods require skill, beginners have to carry out preliminary measurements many times, which wastes a lot of time.

This invention was made in view of this point,
It is an object of the present invention to provide a device that can automatically perform gain adjustment.

[Means for solving the problem] In order to achieve this objective, the automatic gain control device for the nuclear magnetic resonance apparatus of the present invention controls the gain when amplifying the free induction decay signal repeatedly detected in the nuclear magnetic resonance apparatus. An automatic gain control device for controlling an input free induction attenuation signal, the device comprising means for branching an input free induction attenuated signal into two, an amplifier for amplifying one of the branched signals, and an output of the other branched signal. a delay circuit that delays the signal so that it has substantially the same phase as the signal; a determining means that determines the level by detecting the maximum signal level within a predetermined time from the start of detection each time the free induction attenuated signal is detected; The present invention is characterized by comprising a switching means for selectively extracting one free induction attenuation signal from the amplifier or delay circuit based on the determination result of the means.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, reference numeral 1 denotes a divider that takes as an input signal a free induction decay signal (FID signal) obtained by nuclear magnetic resonance measurement and branches this input signal into two. One of the branched signals is sent to a changeover switch 5 via an amplifier 2, a divider 3, and an amplifier 4. The other branched signal is sent to the changeover switch 5 via the delay circuit 6. Further, the signal distributed by the distributor 3 is passed through a delay circuit 7 to a changeover switch 5.
sent to.

A level detector 8 detects the level of an input signal by, for example, envelope detection, and its output signal is sent to a level determination circuit 9. The changeover switch 5 is switched based on the determination signal generated by the determination circuit 9.

The operation of the apparatus having the above-mentioned configuration will be explained using the waveform diagram shown in FIG. FIG. 2a shows the FID signal e0 sent as an input signal. If the gains of the amplifiers 2 and 4 are 2, the output signals e1 and e2 of the amplifiers 2 and 4 are the input signals amplified by 2 and 4 times, respectively. The component e1 that passes through the amplifier 2 has a phase lag from e0, and the component e2 that passes through the amplifier 4 has a further phase lag. Since the delay circuits 6 and 7 delay the phase of e0 and e1 by an amount commensurate with this delay, the signals e0' and e1' that have passed through the delay circuits 6 and 7 have the same phase as e2, and only the amplitude is 1:2: It will be different in the ratio of 4.

Figure 2b shows the level detector 8 that detects the envelope of e0.
and each FID in this output signal
The intensity of the black dot at the beginning of the signal is compared with a plurality of predetermined levels in the level determining circuit 9 as shown in FIG. 2c. For example, the left FID signal in e0 is level “2” and the right FID signal is level “1”
The level is determined as follows. Based on the determination signal indicating such a determination result, the changeover switch 5
For example, e0′ is not amplified during the level “2” period, and it is amplified twice during the level “1” period.
It is switched to take out e1'. As a result, as shown in FIG. 2d, the output of the changeover switch 5 is an FID signal with approximately the same amplitude even if the amplitude of the input signal changes from level "2" to level "1". .

In the above embodiment, an example was given in which the amplifiers were connected in two stages in series, but the present invention can be applied in the same manner even if the amplifiers are connected in one stage or in multiple stages. In that case, fine gain control can be performed by setting the amplifier gains in series such as 20 dB, 10 dB, 5 dB, 2.5 dB, etc.

Also, depending on the FID signal, the beginning part of the signal is not necessarily the largest, so the maximum signal level within a certain period of time from the beginning of the FID signal is detected and the level is determined to determine the gain. You can also do it.
Furthermore, in addition to this, level detection is continued until one FID signal ends, and when a signal exceeding the previously determined level appears, a command is issued to the computer to invalidate the sampling of the FID signal at that time. can also be considered.

[Effects of the Invention] As described in detail above, according to the present invention, a device that can automatically perform gain adjustment is realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining its operation. 1, 3: Distributor, 2, 4: Amplifier, 5: Selector switch, 6, 7: Delay circuit, 8: Level detector,
9: Level judgment circuit.

Claims (1)

[Scope of utility model registration request] An automatic gain control device for controlling the gain when amplifying a free induction decay signal repeatedly detected in a nuclear magnetic resonance apparatus, comprising means for branching an input free induction decay signal into two, and one of the branched signals. a delay circuit that delays the other branched signal so that it has approximately the same phase as the output signal of the amplifier; and a switching means for selectively extracting one free induction attenuated signal from the amplifier or delay circuit based on the determination result of the determining means. An automatic gain control device for a nuclear magnetic resonance apparatus characterized by: