CN103267957A - A NMR spectrometer circuit based on single chip computer - Google Patents

Abstract

The invention discloses a nuclear magnetic resonance spectrometer circuit based on a single chip microcomputer. The nuclear magnetic resonance spectrometer circuit comprises a frequency source module, a pulse generating and transmitting-receiving state switching module connected with the frequency source module, and a signal receiving, processing and displaying module connected with the pulse generating and transmitting-receiving state switching module. The pulse generating and transmitting-receiving state switching module is used for receiving sinusoidal signals from the frequency source module, controlling on-off of an analogue switch by adopting a high-speed single chip microcomputer to generate high-frequency pulse drive signals, wherein the phase difference of the sinusoidal signals is 90 degrees, and the high-frequency pulse drive signals are in various pulse sequences. Meanwhile, the pulse generating and transmitting-receiving state switching module is used for achieving switching of two circuit states, respectively sending of the high-frequency pulse drive signals through control over the analogue switch by the high-speed single chip microcomputer, and receiving of FID signals. The signal receiving, processing and displaying module is used for receiving the FID signals output from the pulse generating and transmitting-receiving state switching module, generating middle-frequency FID signals and transmitting the FID signals to an external display device. Based on the implementation method, the small-size nuclear magnetic resonance spectrometer circuit based on the single chip microcomputer is simple in circuit topological structure, low in manufacturing cost and easy to realize.

Description

A NMR spectrometer circuit based on single chip computer

technical field

The invention relates to a nuclear magnetic resonance spectrometer, in particular to a nuclear magnetic resonance spectrometer circuit based on a single-chip microcomputer.

Background technique

At present, due to the non-destructive and non-radiative advantages of nuclear magnetic resonance detection technology, it has been widely used in medical imaging, material detection and identification and other fields. NMR spectrometers used for substance detection and identification usually consist of magnets, coils and circuit systems. The circuit system mainly includes a radio frequency pulse transmission module, a transceiver conversion module, an FID signal reception module, and a signal processing module. The radio frequency pulse emission module of the conventional nuclear magnetic spectrometer usually stores the pulse sequence information in the SRAM, reads out the pulse sequence information in the SRAM by a microprocessor or a microcomputer, and sends it to the programmable device to generate the high and low levels corresponding to the pulse sequence, and then Pulse trains are generated by a pulse generator. Most of the circuits in the transceiver conversion module and the signal receiving and processing module have also been digitized. The time-domain free attenuation signal FID enters the receiving circuit through the transceiver state conversion switch, and performs digital signal processing after low-noise amplification, frequency conversion, intermediate frequency amplification, and A/D conversion. . However, the traditional nuclear magnetic spectrometer circuit topology and technology are more complicated, and the chips used are expensive.

Contents of the invention

Purpose of the invention: to propose a nuclear magnetic resonance spectrometer circuit based on a single-chip microcomputer, which makes the circuit topology of the nuclear magnetic resonance spectrometer simple and easy to realize miniaturization, and reduces the cost at the same time.

Technical solution: a nuclear magnetic resonance spectrometer circuit based on a single-chip microcomputer, including:

The frequency source module is used to generate three channels of sinusoidal signals, wherein the phase difference between the two channels of sinusoidal signals is 90°;

A pulse generation and transceiver state conversion module connected to the frequency source module; used to receive a sinusoidal signal with a phase difference of 90° from the frequency source module, and use a high-speed single-chip microcomputer to control the on-off of the analog switch to generate various pulses A sequence of high-frequency pulse excitation signals, while using a high-speed single-chip microcomputer to control the analog switch to realize the switching between the transmission of high-frequency pulse excitation signals and the reception of FID signals;

A signal receiving and processing display module connected with the pulse generation and transceiver state conversion module; after receiving the FID signal output by the pulse generation and transceiver state conversion module and performing low-noise amplification, it is connected with the third frequency source module. Mix the sinusoidal signals of two channels to generate an intermediate frequency FID signal and transmit it to an external display device.

The pulse generation and transceiving state transition module includes a pulse generating circuit, a transceiving state transition circuit, and a first single-chip microcomputer; wherein:

The pulse generating circuit includes a first SPDT analog switch, a first SPST analog switch, a buffer, and a power amplifier connected in sequence; the two contacts of the first SPDT analog switch are respectively connected to the two sinusoidal signals of the frequency source module Output terminal, the control end of the first SPDT analog switch is connected to the first I/O port of the first single-chip microcomputer, and the control end of the first SPST analog switch is connected to the second I/O port of the single-chip microcomputer; the first SPDT controlled by the single-chip microcomputer The analog switch selects to receive a sinusoidal signal from the frequency source module, and controls the on-off of the first SPST analog switch to generate a pulse signal, and the pulse signal generates a high-frequency pulse excitation signal after passing through the buffer and the power amplifier;

The transceiving state conversion circuit includes a second SPDT analog switch connected to the power amplifier; the two contacts of the second SPDT analog switch are respectively connected to the output end of the power amplifier and the signal receiving and processing display module , the common end of the second SPDT analog switch is connected to the radio frequency coil of the nuclear magnetic resonance spectrometer, and the control end of the second SPDT analog switch is connected to the third I/O port of the first single-chip microcomputer; the first single-chip microcomputer control The second SPDT analog switch selects to connect the RF coil to the output end of the power amplifier to receive a high-frequency pulse excitation signal for sample excitation, or to connect the RF coil to the signal receiving and processing display module to output an intermediate frequency FID signal to the signal receiving and handle the display module.

Wherein, the frequency source module includes a second single-chip microcomputer, first to third DDS chips connected to the second single-chip microcomputer, and first to third low-pass chips respectively connected to the first to third DDS chips correspondingly The filter also includes a buffer connected to the third low-pass filter, the output of the buffer is connected to the signal receiving and processing display module; the frequency source module adopts direct digital frequency synthesis technology, and adopts the second The single-chip microcomputer controls the first to third DDS chips to generate three sinusoidal signals, wherein the phase difference of the sinusoidal signals output by the first DDS chip and the second DDS chip is 90°, and the third DDS chip outputs the sinusoidal signal to the signal receiving and The processing and display module performs frequency mixing processing with the FID signal output by the pulse generating and transmitting and receiving state conversion module to generate a difference frequency signal.

As an improvement of the present invention, the transceiving state conversion circuit also includes a second SPST analog switch located between the second SPDT analog switch and the signal receiving and processing display module; the control terminal of the second SPST analog switch Connect the fourth I/O port of the first single-chip microcomputer; the second SPST analog switch can isolate the transceiver state conversion circuit and the signal receiving and processing display module under the control of the first single-chip microcomputer.

Beneficial effects: a set of nuclear magnetic resonance spectrometer circuit system with simple topological structure is constructed by using simple and easy-to-implement technology. The components used are cheap and highly integrated, making the entire spectrometer circuit small in size and low in cost. A second SPST analog switch is added between the transceiver state conversion circuit and the signal receiving and processing display module. When the RF coil is connected to the output terminal of the power amplifier, and the high-frequency pulse excitation signal is received for sample excitation, the signal receiving and processing display at this time is improved. The isolation between the module and the high-frequency pulse signal avoids signal interference.

Description of drawings

Fig. 1 is a kind of schematic block diagram of the nuclear magnetic resonance spectrometer circuit system based on the single-chip computer;

Fig. 2 is a block diagram of a sine wave generating circuit with a phase difference of 90°;

Fig. 3 is a circuit block diagram of pulse generation and transceiving state transition;

Fig. 4 is a block diagram of a signal receiving and processing display circuit;

Fig. 5 is the control time sequence of the common pulse of nuclear magnetic resonance spectrometer;

Figure 6 is a block diagram of the nuclear magnetic spectrometer circuit system.

Detailed ways

The present invention will be further explained below in conjunction with the accompanying drawings.

As shown in Figure 1, a nuclear magnetic resonance spectrometer circuit based on a single-chip microcomputer includes: a frequency source module, which is used to generate three sinusoidal signals, and the phase difference between the two sinusoidal signals is 90°. It also includes a pulse generation and transceiver state conversion module connected to the frequency source module, which is used to receive the sinusoidal signal with a phase difference of 90° from the frequency source module and use a high-speed single-chip microcomputer to control the on-off of the analog switch to generate a variety of pulse sequences. The high-frequency pulse excitation signal is used, and the high-speed single-chip computer is used to control the analog switch to realize the conversion of the two circuit states of the high-frequency pulse excitation signal and the FID signal reception. The circuit also includes a signal receiving and processing display module connected to the pulse generating and transmitting and receiving state conversion module, which receives the FID signal output by the pulse generating and transmitting and receiving state conversion module and performs low-noise amplification, and then communicates with the FID signal generated by the frequency source module The third sinusoidal signal is mixed to generate an intermediate frequency FID signal and then transmitted to an external display device.

As shown in Figure 2, the frequency source module is used to generate two sinusoidal signals with a phase difference of 90°. The circuit part includes a single-chip microcomputer 2, a DDS chip 1 and a DDS chip 2 connected to the single-chip microcomputer 2, and a low-pass filter 1 and a low-pass filter 2 respectively connected to the DDS chip 1 and DDS chip 2. A DDS chip provides the clock signal. The frequency source module adopts direct digital frequency synthesis technology. When the single-chip microcomputer 2 writes the frequency control word and phase control word to the two DDS chips, the single-chip microcomputer 2 sends a control signal to the two DDS chips at the same time to make the output of the two DDS chips The phase of the sinusoidal signal is consistent with the set frequency, so a sinusoidal signal with a specified frequency and a phase difference of 90° is obtained at the output terminals of the two DDS chips.

As shown in FIG. 3 , the pulse generation and transceiver state conversion module includes a pulse generation circuit, a transceiver state conversion circuit, and a single-chip microcomputer 1 . Wherein: the pulse generating circuit includes a SPDT1 analog switch, an SPST1 analog switch, a buffer, and a power amplifier connected in sequence. The two contacts of the SPDT1 analog switch are respectively connected to the two sinusoidal signal output terminals of the frequency source module, the common end of the SPDT1 analog switch is connected to the SPST1 analog switch, the control end of the SPDT1 analog switch is connected to the P1. The control end of the switch is connected to the P1.0 port of the microcontroller 1. The on-off of the SPDT1 analog switch is controlled by the high and low level signals of the I/O port of the high-speed single-chip microcomputer 1. The single-channel sinusoidal signal output from the SPDT1 analog switch is connected to the SPST1 analog switch. The continuous sinusoidal signal is truncated into a radio frequency pulse whose pulse width and pulse interval meet the requirements, and the radio frequency pulse passes through a buffer and a power amplifier to output a high frequency radio frequency pulse excitation signal that meets the requirements.

The transceiver state conversion circuit includes SPDT2 analog switch and SPST2 analog switch. The two contacts of the SPDT2 analog switch are respectively connected to the output end of the power amplifier and the SPST2 analog switch. The common end of the SPDT2 analog switch is connected to the radio frequency coil of the nuclear magnetic resonance spectrometer, and the other end of the SPST2 analog switch is connected to the signal receiving and processing display module. The control end of the SPDT2 analog switch is connected to the P1.1 port of the single-chip microcomputer 1, and the control end of the SPST2 analog switch is connected to the P1.2 port of the single-chip microcomputer 1. The transmission and reception state conversion device of the nuclear magnetic resonance spectrometer circuit is realized by using a high-speed single-chip microcomputer 1 to control a SPDT2 analog switch with high isolation and low insertion loss. When the circuit works in the sample excitation state, the high-power high-frequency pulse enters the radio frequency coil through the SPDT2 analog switch to generate a radio frequency magnetic field. Under the action of the radio frequency magnetic field, the sample undergoes a nuclear magnetic resonance phenomenon to generate a nuclear magnetic resonance signal. During radio frequency pulse transmission, there needs to be a high degree of isolation between the pulse transmission circuit and the signal receiving and processing display module, otherwise a slight pulse leakage into the receiving circuit may burn out the components in the receiving circuit. In order to overcome the defect that the isolation of the SPDT2 analog switch is not high enough, a low insertion loss SPST2 analog switch is connected in series in the receiving circuit. During the radio frequency pulse transmission period, the analog switch is reliably turned off by the high-speed single-chip microcomputer 1. During the FID signal receiving process The switch is turned on.

As shown in Figure 4, the signal receiving and processing display module includes a FID signal receiving circuit and a signal processing display circuit. The FID signal receiving circuit is mainly composed of a low-noise preamplifier LNA (LNA: Low Noise Amplifier), a mixer, a low-pass filter 4 and an intermediate frequency amplifier connected in sequence. Wherein, frequency source module also comprises the DDS chip 3 that is connected with single-chip microcomputer 2, and the low-pass filter 3 that is connected with DDS chip 3, and the buffer that is connected with low-pass filter 3; Control DDS chip 3 to generate local The oscillating signal is then sent to the mixer. When the RF coil is connected to the signal receiving and processing module, the weak FID signal output by the transceiver state conversion circuit is initially amplified by the low-noise preamplifier LNA, and then enters the mixer for mixing with the local oscillation signal, and the mixed signal passes through The difference frequency signal between the FID signal and the local oscillator signal is obtained after the low-pass filter 4, and the amplitude of the signal is further increased after being amplified by the intermediate frequency, so as to observe the signal and digitally collect the signal with an oscilloscope.

In the signal processing and display circuit, the signal output by the intermediate frequency amplifier is first converted into a digital signal by A/D conversion, and then communicated with the computer by the single chip microcomputer, and the collected intermediate frequency FID signal is uploaded to the microcomputer for processing and display.

As shown in Figure 5, if SPST1 and SPST2 are turned on at a high level and turned off at a low level, only the Sin1 signal output by the low-pass filter 1 can pass when SPDT1 is connected to a low level, and only the Sin1 signal output by the low-pass filter 2 can pass when it is connected to a high level. The output Sin2 signal can pass through. When SPDT2 is connected to a low level, the coil is connected to the transmitting circuit, and when connected to a high level, the coil is connected to the receiving circuit. The on-off of the four analog electronic switches are all controlled by the single-chip microcomputer 1 with high-speed instruction execution speed. SPDT1 is used to select which sine wave signal is input, and SPST1 is used to truncate the continuous wave signal to generate a pulse sequence whose pulse width and pulse interval meet the requirements. When SPDT2 works in the state of pulse transmission, SPST2 is reliably turned off to reduce the impact of the signal leaked from the transmission circuit on the reception circuit. Figure 5 shows the control timing of common pulses used in nuclear magnetic resonance spectrometers. Only the Sin1 signal is used when generating spin echo sequences and CP sequences. When generating a CPMG sequence, the 90° pulse uses the Sin1 signal, and the 180° pulse after the 90° pulse uses the Sin2 signal. Among the three pulse sequences, the SPDT2 switch connects the RF coil with the receiving circuit only during the process of receiving the FID signal, and the SPST2 analog switch remains connected only during the process of receiving the FID signal.

As shown in FIG. 6, the overall connection block diagram of the nuclear magnetic spectrometer circuit system based on the single-chip microcomputer of this embodiment.

The above is only a preferred embodiment of the present invention, it should be pointed out that, for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (4)

1. a nuclear magnetic resonance spectrometer circuit based on a single-chip microcomputer, is characterized in that: comprising: The frequency source module is used to generate three channels of sinusoidal signals, wherein the phase difference between the two channels of sinusoidal signals is 90°; A pulse generation and transceiver state conversion module connected to the frequency source module; used to receive a sinusoidal signal with a phase difference of 90° from the frequency source module, and use a high-speed single-chip microcomputer to control the on-off of the analog switch to generate various pulses A sequence of high-frequency pulse excitation signals, while using a high-speed single-chip microcomputer to control the analog switch to realize the switching between the transmission of high-frequency pulse excitation signals and the reception of FID signals; A signal receiving and processing display module connected with the pulse generation and transceiver state conversion module; after receiving the FID signal output by the pulse generation and transceiver state conversion module and performing low-noise amplification, it is connected with the third frequency source module. Mix the sinusoidal signals of two channels to generate an intermediate frequency FID signal and transmit it to an external display device. 2. a kind of nuclear magnetic resonance spectrometer circuit based on single-chip microcomputer according to claim 1, is characterized in that: described pulse generation and transceiving state transition module comprise pulse generation circuit, transceiving state transition circuit, the first single-chip microcomputer; in: The pulse generating circuit includes a first SPDT analog switch, a first SPST analog switch, a buffer, and a power amplifier connected in sequence; the two contacts of the first SPDT analog switch are respectively connected to the two sinusoidal signals of the frequency source module Output terminal, the control end of the first SPDT analog switch is connected to the first I/O port of the first single-chip microcomputer, and the control end of the first SPST analog switch is connected to the second I/O port of the single-chip microcomputer; the first SPDT controlled by the single-chip microcomputer The analog switch selects to receive a sinusoidal signal from the frequency source module, and controls the on-off of the first SPST analog switch to generate a pulse signal, and the pulse signal generates a high-frequency pulse excitation signal after passing through the buffer and the power amplifier; The transceiving state conversion circuit includes a second SPDT analog switch connected to the power amplifier; the two contacts of the second SPDT analog switch are respectively connected to the output end of the power amplifier and the signal receiving and processing display module , the common end of the second SPDT analog switch is connected to the radio frequency coil of the nuclear magnetic resonance spectrometer, and the control end of the second SPDT analog switch is connected to the third I/O port of the first single-chip microcomputer; the first single-chip microcomputer control The second SPDT analog switch selects to connect the RF coil to the output end of the power amplifier to receive a high-frequency pulse excitation signal for sample excitation, or to connect the RF coil to the signal receiving and processing display module to output an intermediate frequency FID signal to the signal receiving and handle the display module. 3. a kind of nuclear magnetic resonance spectrometer circuit based on single-chip microcomputer according to claim 1, is characterized in that: described frequency source module comprises second single-chip microcomputer, the first to the 3rd DDS chip that is connected with described second single-chip microcomputer, And the first to third low-pass filters correspondingly connected to the first to third DDS chips respectively, also include a buffer connected to the third low-pass filter, the output end of the buffer is connected to the signal Receiving and processing display module; the frequency source module adopts direct digital frequency synthesis technology, and uses the second single-chip microcomputer to control the first to third DDS chips to generate three-way sinusoidal signals, wherein the sinusoidal signals output by the first DDS chip and the second DDS chip The signal phase difference is 90°, the third DDS chip outputs a sinusoidal signal to the signal receiving and processing display module, and performs frequency mixing processing with the FID signal output by the pulse generating and transmitting and receiving state conversion module to generate a difference frequency signal. 4. A kind of nuclear magnetic resonance spectrometer circuit based on a single-chip microcomputer according to claim 2, characterized in that: said transceiver state conversion circuit also includes a signal receiving and processing display module located between said second SPDT analog switch and said signal receiving and processing display module The second SPST analog switch between; the control terminal of the second SPST analog switch is connected to the fourth I/O port of the first single-chip microcomputer; the second SPST analog switch can be isolated under the control of the first single-chip microcomputer The transceiving state conversion circuit and the signal receiving and processing display module.

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