JPH0560849A - Function pulse generator - Google Patents

Abstract

PURPOSE:To input a function pulse with an accurate waveform to an NMR probe in an NMR. CONSTITUTION:A function signal 23 which is read from a function signal generator 12 and is converted to an analog signal by a D/A converter 13 is subjected to waveform compensation according to a non-linearity of a function pulse signal system or an amount of attenuation. The function signal 23 is mixed to an RF pulse signal 24 by a mixer 17, thus enabling a function pulse signal 25 to be generated. The function pulse signal 25 is attenuated by a specified amount by a variable attenuator 18 and is input to an NMR probe 21 through a power amplifier 19 and a duplexer 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a function pulse generator suitable for generating a function pulse used as an excitation pulse particularly in NMR.

[0002]

2. Description of the Related Art Conventionally, when it is desired to excite only a specific frequency region of a sample in NMR, an excitation pulse is a sink (SINC) function, a Gauss (GAUSS) function, or a Hermite (HERMITE) function as shown in FIGS. Function pulses such as functions and half Gauss (HAFEGAUSS) functions are used. A schematic configuration for generating the function pulse is shown in FIG. In FIG. 6, the function pulse generator 1 generates the function pulse shown in FIG. 5A, B, C or D, and the generated function pulse is attenuated by the variable attenuator 2 by a predetermined amount to an appropriate power level. After being controlled so that it is controlled by the power amplifier, it is amplified by the power amplifier and input to the NMR probe 5 via the duplexer 4. Then, the FID signal output from the NMR probe 5 is input to the head amplifier 6 via the duplexer 4, amplified, and used for analysis.

[0003]

However, the input / output characteristics of the signal system composed of the variable attenuator 2, the power amplifier 3, and the duplexer 4 are non-linear as shown by the curve 7 in FIG. Output characteristics are variable attenuator 2
Since the function pulse generator 1 changes as shown in the curve 8 or 9 according to the amount of attenuation, the function pulse input to the NMR probe 5 is accompanied by distortion even if the function pulse generator 1 generates an accurate mathematical function pulse. Therefore, there is a problem that the excitation distribution deteriorates and the selectivity of the excitation deteriorates.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a function pulse generator capable of inputting a mathematically determined accurate function pulse to an NMR probe. is there.

[0005]

To achieve the above object, a function pulse generator of the present invention comprises a function signal generator for generating a function signal having a predetermined waveform, a high frequency pulse generator, and A function pulse generator that generates a function pulse signal from the output of the function signal generator and the output of the high frequency pulse generator, a variable attenuator that changes the intensity of the function pulse signal, and a subsequent circuit after the variable attenuator In the function pulse generator comprising, the function signal generator,
It is characterized in that the function pulse signal is for generating a function signal having a waveform without distortion when the function pulse signal passes through the variable attenuator and the latter-stage circuit.

[0006]

The function signal generator outputs a function signal having a predetermined waveform. The function signal waveform is a function pulse signal system in which the function pulse signal has a variable attenuator and a subsequent circuit thereafter. It is set so as to have a waveform with no distortion at the time of passing. This function signal is input to the function pulse generator, and the function pulse signal is generated with the high frequency pulse signal output from the high frequency pulse generator. The intensity of the function pulse signal is adjusted by a predetermined amount by the variable attenuator and then passes through the subsequent circuit. At this point, the waveform of the function pulse signal is not distorted.

[0007]

Embodiments will be described below with reference to the drawings.
FIG. 1 is a diagram showing the configuration of an embodiment of a function pulse generator according to the present invention, in which 10 is a clock generator and 11 is a clock generator.
Is an address counter, 12 is a function signal generator, and 13 is D
/ A converter, 14 variable attenuator controller, 15 function signal selector, 16 RF pulse generator, 17 mixer, 18 variable attenuator, 19 power amplifier, 20 duplexer, 21 NMR probe , 22 is a head amplifier, 23 is a function signal, 24 is an RF pulse signal, and 25 is a function pulse signal.

In FIG. 1, a clock generator 10 generates a clock signal having a predetermined frequency, and an address counter 11 counts clocks generated by the clock generator 10 to generate an address.
The function signal generator 12 is composed of a ROM, and the data written in the addresses generated by the address counter 11 are sequentially output. In the ROM, as shown in FIG. 2, a function value corrected corresponding to the attenuation amount of the variable attenuator 18 is written for each function signal such as a sinc function, a Gaussian function, a Hermitian function, and a half Gaussian function. Has been.
This function value is a value corrected to cancel the nonlinearity of the input / output characteristics of the function pulse signal signal system including the variable attenuator 18, the power amplifier 19, and the duplexer 20, and the output of the mixer 17 The function pulse signal 25 is a variable attenuator 18, a power amplifier 19, a duplexer 2
The value is such that the input / output characteristic of the entire function pulse signal system becomes a straight line as shown in FIG.

The function value read from the function signal generator 12 is converted into an analog signal by the D / A converter 13 and input to the mixer 17. The function signal selector 15 indicates which function signal is read from the functions stored in the function signal generator 12. Therefore, when the function signal selector 15 indicates the sink function and the variable attenuator controller 14 indicates the attenuation amount G ₀ , the function signal generator 12 outputs H based on the address from the address counter 11. Function values of ₀₀ , H ₀₁ , ..., H _0M are sequentially output and converted into an analog signal to generate a function signal 23.

The RF pulse signal 24 from the RF pulse generator 16 is also input to the mixer 17, and is mixed with the function signal 23 to generate the function pulse signal 25. Then, the function pulse signal 25 is attenuated in the variable attenuator 18 by the attenuation amount instructed by the variable attenuator controller 14,
NMR via power amplifier 19 and duplexer 20
Input to the probe 21. It is clear that the function pulse signal at this time has an accurate waveform as mathematically determined. The FID signal from the NMR probe 21 is input to the head amplifier 22 via the duplexer 20 as in the conventional case.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications can be made. For example, although the mixer is used to generate the function pulse signal from the function signal and the RF pulse signal in the above embodiment, the variable attenuator 25 is provided as shown in FIG. Signal 24
It is also possible to obtain a function pulse signal by dynamically controlling the intensity of the function signal 23.
Besides correcting the waveform of the function signal according to the amount of attenuation of the variable attenuator, the function signal or the waveform of the function pulse signal can be corrected according to the frequency of the RF pulse signal.

[0012]

As is apparent from the above description, according to the present invention, the waveform of the function signal can be determined according to the nonlinearity of the input / output characteristics of the function pulse signal system and the attenuation amount of the variable attenuator. Since the correction is performed, the non-linearity of the signal system of the function pulse signal can be corrected, so that the function pulse signal for excitation input to the NMR probe can have a correct waveform mathematically obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a diagram showing a structural example of a ROM of a function signal generator.

FIG. 3 is a diagram for explaining the effect of the present invention.

FIG. 4 is a diagram showing a modification of the configuration of FIG.

FIG. 5 is a diagram showing a waveform of a function pulse signal for excitation.

FIG. 6 is a diagram showing a configuration example of a conventional function pulse generator.

FIG. 7 is a diagram for explaining a problem of a conventional function pulse generator.

[Explanation of symbols]

10 ... Clock generator, 11 ... Address counter, 12
... Function signal generator, 13 ... D / A converter, 14 ... Variable attenuator controller, 15 ... Function signal selector, 16 ... RF
Pulse generator, 17 ... Mixer, 18 ... Variable attenuator, 19
… Power amplifier, 20… Duplexer, 21… NMR
Probe, 22 ... Head amplifier, 23 ... Function signal, 24
... RF pulse signal, 25 ... Function pulse signal.

Claims (2)

[Claims] 1. A function signal generator for generating a function signal having a predetermined waveform, a high frequency pulse generator, and a function pulse signal generated from the output of the function signal generator and the output of the high frequency pulse generator. In a function pulse generator including a function pulse generator, a variable attenuator for varying the intensity of the function pulse signal, and a subsequent circuit after the variable attenuator, the function signal generator is characterized in that the function pulse signal is variable. A function pulse generator, which generates a function signal having a waveform without distortion when passing through an attenuator and the latter-stage circuit. 2. The function pulse generator according to claim 1, wherein the function signal generator generates a function signal according to an attenuation amount of the variable attenuator.